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// SPDX-License-Identifier: GPL-2.0-or-later | |
/* | |
* Fast Userspace Mutexes (which I call "Futexes!"). | |
* (C) Rusty Russell, IBM 2002 | |
* | |
* Generalized futexes, futex requeueing, misc fixes by Ingo Molnar | |
* (C) Copyright 2003 Red Hat Inc, All Rights Reserved | |
* | |
* Removed page pinning, fix privately mapped COW pages and other cleanups | |
* (C) Copyright 2003, 2004 Jamie Lokier | |
* | |
* Robust futex support started by Ingo Molnar | |
* (C) Copyright 2006 Red Hat Inc, All Rights Reserved | |
* Thanks to Thomas Gleixner for suggestions, analysis and fixes. | |
* | |
* PI-futex support started by Ingo Molnar and Thomas Gleixner | |
* Copyright (C) 2006 Red Hat, Inc., Ingo Molnar <mingo@redhat.com> | |
* Copyright (C) 2006 Timesys Corp., Thomas Gleixner <tglx@timesys.com> | |
* | |
* PRIVATE futexes by Eric Dumazet | |
* Copyright (C) 2007 Eric Dumazet <dada1@cosmosbay.com> | |
* | |
* Requeue-PI support by Darren Hart <dvhltc@us.ibm.com> | |
* Copyright (C) IBM Corporation, 2009 | |
* Thanks to Thomas Gleixner for conceptual design and careful reviews. | |
* | |
* Thanks to Ben LaHaise for yelling "hashed waitqueues" loudly | |
* enough at me, Linus for the original (flawed) idea, Matthew | |
* Kirkwood for proof-of-concept implementation. | |
* | |
* "The futexes are also cursed." | |
* "But they come in a choice of three flavours!" | |
*/ | |
#include <linux/compat.h> | |
#include <linux/jhash.h> | |
#include <linux/pagemap.h> | |
#include <linux/syscalls.h> | |
#include <linux/hugetlb.h> | |
#include <linux/freezer.h> | |
#include <linux/memblock.h> | |
#include <linux/fault-inject.h> | |
#include <linux/time_namespace.h> | |
#include <asm/futex.h> | |
#include "locking/rtmutex_common.h" | |
/* | |
* READ this before attempting to hack on futexes! | |
* | |
* Basic futex operation and ordering guarantees | |
* ============================================= | |
* | |
* The waiter reads the futex value in user space and calls | |
* futex_wait(). This function computes the hash bucket and acquires | |
* the hash bucket lock. After that it reads the futex user space value | |
* again and verifies that the data has not changed. If it has not changed | |
* it enqueues itself into the hash bucket, releases the hash bucket lock | |
* and schedules. | |
* | |
* The waker side modifies the user space value of the futex and calls | |
* futex_wake(). This function computes the hash bucket and acquires the | |
* hash bucket lock. Then it looks for waiters on that futex in the hash | |
* bucket and wakes them. | |
* | |
* In futex wake up scenarios where no tasks are blocked on a futex, taking | |
* the hb spinlock can be avoided and simply return. In order for this | |
* optimization to work, ordering guarantees must exist so that the waiter | |
* being added to the list is acknowledged when the list is concurrently being | |
* checked by the waker, avoiding scenarios like the following: | |
* | |
* CPU 0 CPU 1 | |
* val = *futex; | |
* sys_futex(WAIT, futex, val); | |
* futex_wait(futex, val); | |
* uval = *futex; | |
* *futex = newval; | |
* sys_futex(WAKE, futex); | |
* futex_wake(futex); | |
* if (queue_empty()) | |
* return; | |
* if (uval == val) | |
* lock(hash_bucket(futex)); | |
* queue(); | |
* unlock(hash_bucket(futex)); | |
* schedule(); | |
* | |
* This would cause the waiter on CPU 0 to wait forever because it | |
* missed the transition of the user space value from val to newval | |
* and the waker did not find the waiter in the hash bucket queue. | |
* | |
* The correct serialization ensures that a waiter either observes | |
* the changed user space value before blocking or is woken by a | |
* concurrent waker: | |
* | |
* CPU 0 CPU 1 | |
* val = *futex; | |
* sys_futex(WAIT, futex, val); | |
* futex_wait(futex, val); | |
* | |
* waiters++; (a) | |
* smp_mb(); (A) <-- paired with -. | |
* | | |
* lock(hash_bucket(futex)); | | |
* | | |
* uval = *futex; | | |
* | *futex = newval; | |
* | sys_futex(WAKE, futex); | |
* | futex_wake(futex); | |
* | | |
* `--------> smp_mb(); (B) | |
* if (uval == val) | |
* queue(); | |
* unlock(hash_bucket(futex)); | |
* schedule(); if (waiters) | |
* lock(hash_bucket(futex)); | |
* else wake_waiters(futex); | |
* waiters--; (b) unlock(hash_bucket(futex)); | |
* | |
* Where (A) orders the waiters increment and the futex value read through | |
* atomic operations (see hb_waiters_inc) and where (B) orders the write | |
* to futex and the waiters read (see hb_waiters_pending()). | |
* | |
* This yields the following case (where X:=waiters, Y:=futex): | |
* | |
* X = Y = 0 | |
* | |
* w[X]=1 w[Y]=1 | |
* MB MB | |
* r[Y]=y r[X]=x | |
* | |
* Which guarantees that x==0 && y==0 is impossible; which translates back into | |
* the guarantee that we cannot both miss the futex variable change and the | |
* enqueue. | |
* | |
* Note that a new waiter is accounted for in (a) even when it is possible that | |
* the wait call can return error, in which case we backtrack from it in (b). | |
* Refer to the comment in queue_lock(). | |
* | |
* Similarly, in order to account for waiters being requeued on another | |
* address we always increment the waiters for the destination bucket before | |
* acquiring the lock. It then decrements them again after releasing it - | |
* the code that actually moves the futex(es) between hash buckets (requeue_futex) | |
* will do the additional required waiter count housekeeping. This is done for | |
* double_lock_hb() and double_unlock_hb(), respectively. | |
*/ | |
#ifdef CONFIG_HAVE_FUTEX_CMPXCHG | |
#define futex_cmpxchg_enabled 1 | |
#else | |
static int __read_mostly futex_cmpxchg_enabled; | |
#endif | |
/* | |
* Futex flags used to encode options to functions and preserve them across | |
* restarts. | |
*/ | |
#ifdef CONFIG_MMU | |
# define FLAGS_SHARED 0x01 | |
#else | |
/* | |
* NOMMU does not have per process address space. Let the compiler optimize | |
* code away. | |
*/ | |
# define FLAGS_SHARED 0x00 | |
#endif | |
#define FLAGS_CLOCKRT 0x02 | |
#define FLAGS_HAS_TIMEOUT 0x04 | |
/* | |
* Priority Inheritance state: | |
*/ | |
struct futex_pi_state { | |
/* | |
* list of 'owned' pi_state instances - these have to be | |
* cleaned up in do_exit() if the task exits prematurely: | |
*/ | |
struct list_head list; | |
/* | |
* The PI object: | |
*/ | |
struct rt_mutex pi_mutex; | |
struct task_struct *owner; | |
refcount_t refcount; | |
union futex_key key; | |
} __randomize_layout; | |
/** | |
* struct futex_q - The hashed futex queue entry, one per waiting task | |
* @list: priority-sorted list of tasks waiting on this futex | |
* @task: the task waiting on the futex | |
* @lock_ptr: the hash bucket lock | |
* @key: the key the futex is hashed on | |
* @pi_state: optional priority inheritance state | |
* @rt_waiter: rt_waiter storage for use with requeue_pi | |
* @requeue_pi_key: the requeue_pi target futex key | |
* @bitset: bitset for the optional bitmasked wakeup | |
* | |
* We use this hashed waitqueue, instead of a normal wait_queue_entry_t, so | |
* we can wake only the relevant ones (hashed queues may be shared). | |
* | |
* A futex_q has a woken state, just like tasks have TASK_RUNNING. | |
* It is considered woken when plist_node_empty(&q->list) || q->lock_ptr == 0. | |
* The order of wakeup is always to make the first condition true, then | |
* the second. | |
* | |
* PI futexes are typically woken before they are removed from the hash list via | |
* the rt_mutex code. See unqueue_me_pi(). | |
*/ | |
struct futex_q { | |
struct plist_node list; | |
struct task_struct *task; | |
spinlock_t *lock_ptr; | |
union futex_key key; | |
struct futex_pi_state *pi_state; | |
struct rt_mutex_waiter *rt_waiter; | |
union futex_key *requeue_pi_key; | |
u32 bitset; | |
} __randomize_layout; | |
static const struct futex_q futex_q_init = { | |
/* list gets initialized in queue_me()*/ | |
.key = FUTEX_KEY_INIT, | |
.bitset = FUTEX_BITSET_MATCH_ANY | |
}; | |
/* | |
* Hash buckets are shared by all the futex_keys that hash to the same | |
* location. Each key may have multiple futex_q structures, one for each task | |
* waiting on a futex. | |
*/ | |
struct futex_hash_bucket { | |
atomic_t waiters; | |
spinlock_t lock; | |
struct plist_head chain; | |
} ____cacheline_aligned_in_smp; | |
/* | |
* The base of the bucket array and its size are always used together | |
* (after initialization only in hash_futex()), so ensure that they | |
* reside in the same cacheline. | |
*/ | |
static struct { | |
struct futex_hash_bucket *queues; | |
unsigned long hashsize; | |
} __futex_data __read_mostly __aligned(2*sizeof(long)); | |
#define futex_queues (__futex_data.queues) | |
#define futex_hashsize (__futex_data.hashsize) | |
/* | |
* Fault injections for futexes. | |
*/ | |
#ifdef CONFIG_FAIL_FUTEX | |
static struct { | |
struct fault_attr attr; | |
bool ignore_private; | |
} fail_futex = { | |
.attr = FAULT_ATTR_INITIALIZER, | |
.ignore_private = false, | |
}; | |
static int __init setup_fail_futex(char *str) | |
{ | |
return setup_fault_attr(&fail_futex.attr, str); | |
} | |
__setup("fail_futex=", setup_fail_futex); | |
static bool should_fail_futex(bool fshared) | |
{ | |
if (fail_futex.ignore_private && !fshared) | |
return false; | |
return should_fail(&fail_futex.attr, 1); | |
} | |
#ifdef CONFIG_FAULT_INJECTION_DEBUG_FS | |
static int __init fail_futex_debugfs(void) | |
{ | |
umode_t mode = S_IFREG | S_IRUSR | S_IWUSR; | |
struct dentry *dir; | |
dir = fault_create_debugfs_attr("fail_futex", NULL, | |
&fail_futex.attr); | |
if (IS_ERR(dir)) | |
return PTR_ERR(dir); | |
debugfs_create_bool("ignore-private", mode, dir, | |
&fail_futex.ignore_private); | |
return 0; | |
} | |
late_initcall(fail_futex_debugfs); | |
#endif /* CONFIG_FAULT_INJECTION_DEBUG_FS */ | |
#else | |
static inline bool should_fail_futex(bool fshared) | |
{ | |
return false; | |
} | |
#endif /* CONFIG_FAIL_FUTEX */ | |
#ifdef CONFIG_COMPAT | |
static void compat_exit_robust_list(struct task_struct *curr); | |
#endif | |
/* | |
* Reflects a new waiter being added to the waitqueue. | |
*/ | |
static inline void hb_waiters_inc(struct futex_hash_bucket *hb) | |
{ | |
#ifdef CONFIG_SMP | |
atomic_inc(&hb->waiters); | |
/* | |
* Full barrier (A), see the ordering comment above. | |
*/ | |
smp_mb__after_atomic(); | |
#endif | |
} | |
/* | |
* Reflects a waiter being removed from the waitqueue by wakeup | |
* paths. | |
*/ | |
static inline void hb_waiters_dec(struct futex_hash_bucket *hb) | |
{ | |
#ifdef CONFIG_SMP | |
atomic_dec(&hb->waiters); | |
#endif | |
} | |
static inline int hb_waiters_pending(struct futex_hash_bucket *hb) | |
{ | |
#ifdef CONFIG_SMP | |
/* | |
* Full barrier (B), see the ordering comment above. | |
*/ | |
smp_mb(); | |
return atomic_read(&hb->waiters); | |
#else | |
return 1; | |
#endif | |
} | |
/** | |
* hash_futex - Return the hash bucket in the global hash | |
* @key: Pointer to the futex key for which the hash is calculated | |
* | |
* We hash on the keys returned from get_futex_key (see below) and return the | |
* corresponding hash bucket in the global hash. | |
*/ | |
static struct futex_hash_bucket *hash_futex(union futex_key *key) | |
{ | |
u32 hash = jhash2((u32 *)key, offsetof(typeof(*key), both.offset) / 4, | |
key->both.offset); | |
return &futex_queues[hash & (futex_hashsize - 1)]; | |
} | |
/** | |
* match_futex - Check whether two futex keys are equal | |
* @key1: Pointer to key1 | |
* @key2: Pointer to key2 | |
* | |
* Return 1 if two futex_keys are equal, 0 otherwise. | |
*/ | |
static inline int match_futex(union futex_key *key1, union futex_key *key2) | |
{ | |
return (key1 && key2 | |
&& key1->both.word == key2->both.word | |
&& key1->both.ptr == key2->both.ptr | |
&& key1->both.offset == key2->both.offset); | |
} | |
enum futex_access { | |
FUTEX_READ, | |
FUTEX_WRITE | |
}; | |
/** | |
* futex_setup_timer - set up the sleeping hrtimer. | |
* @time: ptr to the given timeout value | |
* @timeout: the hrtimer_sleeper structure to be set up | |
* @flags: futex flags | |
* @range_ns: optional range in ns | |
* | |
* Return: Initialized hrtimer_sleeper structure or NULL if no timeout | |
* value given | |
*/ | |
static inline struct hrtimer_sleeper * | |
futex_setup_timer(ktime_t *time, struct hrtimer_sleeper *timeout, | |
int flags, u64 range_ns) | |
{ | |
if (!time) | |
return NULL; | |
hrtimer_init_sleeper_on_stack(timeout, (flags & FLAGS_CLOCKRT) ? | |
CLOCK_REALTIME : CLOCK_MONOTONIC, | |
HRTIMER_MODE_ABS); | |
/* | |
* If range_ns is 0, calling hrtimer_set_expires_range_ns() is | |
* effectively the same as calling hrtimer_set_expires(). | |
*/ | |
hrtimer_set_expires_range_ns(&timeout->timer, *time, range_ns); | |
return timeout; | |
} | |
/* | |
* Generate a machine wide unique identifier for this inode. | |
* | |
* This relies on u64 not wrapping in the life-time of the machine; which with | |
* 1ns resolution means almost 585 years. | |
* | |
* This further relies on the fact that a well formed program will not unmap | |
* the file while it has a (shared) futex waiting on it. This mapping will have | |
* a file reference which pins the mount and inode. | |
* | |
* If for some reason an inode gets evicted and read back in again, it will get | |
* a new sequence number and will _NOT_ match, even though it is the exact same | |
* file. | |
* | |
* It is important that match_futex() will never have a false-positive, esp. | |
* for PI futexes that can mess up the state. The above argues that false-negatives | |
* are only possible for malformed programs. | |
*/ | |
static u64 get_inode_sequence_number(struct inode *inode) | |
{ | |
static atomic64_t i_seq; | |
u64 old; | |
/* Does the inode already have a sequence number? */ | |
old = atomic64_read(&inode->i_sequence); | |
if (likely(old)) | |
return old; | |
for (;;) { | |
u64 new = atomic64_add_return(1, &i_seq); | |
if (WARN_ON_ONCE(!new)) | |
continue; | |
old = atomic64_cmpxchg_relaxed(&inode->i_sequence, 0, new); | |
if (old) | |
return old; | |
return new; | |
} | |
} | |
/** | |
* get_futex_key() - Get parameters which are the keys for a futex | |
* @uaddr: virtual address of the futex | |
* @fshared: false for a PROCESS_PRIVATE futex, true for PROCESS_SHARED | |
* @key: address where result is stored. | |
* @rw: mapping needs to be read/write (values: FUTEX_READ, | |
* FUTEX_WRITE) | |
* | |
* Return: a negative error code or 0 | |
* | |
* The key words are stored in @key on success. | |
* | |
* For shared mappings (when @fshared), the key is: | |
* | |
* ( inode->i_sequence, page->index, offset_within_page ) | |
* | |
* [ also see get_inode_sequence_number() ] | |
* | |
* For private mappings (or when !@fshared), the key is: | |
* | |
* ( current->mm, address, 0 ) | |
* | |
* This allows (cross process, where applicable) identification of the futex | |
* without keeping the page pinned for the duration of the FUTEX_WAIT. | |
* | |
* lock_page() might sleep, the caller should not hold a spinlock. | |
*/ | |
static int get_futex_key(u32 __user *uaddr, bool fshared, union futex_key *key, | |
enum futex_access rw) | |
{ | |
unsigned long address = (unsigned long)uaddr; | |
struct mm_struct *mm = current->mm; | |
struct page *page, *tail; | |
struct address_space *mapping; | |
int err, ro = 0; | |
/* | |
* The futex address must be "naturally" aligned. | |
*/ | |
key->both.offset = address % PAGE_SIZE; | |
if (unlikely((address % sizeof(u32)) != 0)) | |
return -EINVAL; | |
address -= key->both.offset; | |
if (unlikely(!access_ok(uaddr, sizeof(u32)))) | |
return -EFAULT; | |
if (unlikely(should_fail_futex(fshared))) | |
return -EFAULT; | |
/* | |
* PROCESS_PRIVATE futexes are fast. | |
* As the mm cannot disappear under us and the 'key' only needs | |
* virtual address, we dont even have to find the underlying vma. | |
* Note : We do have to check 'uaddr' is a valid user address, | |
* but access_ok() should be faster than find_vma() | |
*/ | |
if (!fshared) { | |
key->private.mm = mm; | |
key->private.address = address; | |
return 0; | |
} | |
again: | |
/* Ignore any VERIFY_READ mapping (futex common case) */ | |
if (unlikely(should_fail_futex(true))) | |
return -EFAULT; | |
err = get_user_pages_fast(address, 1, FOLL_WRITE, &page); | |
/* | |
* If write access is not required (eg. FUTEX_WAIT), try | |
* and get read-only access. | |
*/ | |
if (err == -EFAULT && rw == FUTEX_READ) { | |
err = get_user_pages_fast(address, 1, 0, &page); | |
ro = 1; | |
} | |
if (err < 0) | |
return err; | |
else | |
err = 0; | |
/* | |
* The treatment of mapping from this point on is critical. The page | |
* lock protects many things but in this context the page lock | |
* stabilizes mapping, prevents inode freeing in the shared | |
* file-backed region case and guards against movement to swap cache. | |
* | |
* Strictly speaking the page lock is not needed in all cases being | |
* considered here and page lock forces unnecessarily serialization | |
* From this point on, mapping will be re-verified if necessary and | |
* page lock will be acquired only if it is unavoidable | |
* | |
* Mapping checks require the head page for any compound page so the | |
* head page and mapping is looked up now. For anonymous pages, it | |
* does not matter if the page splits in the future as the key is | |
* based on the address. For filesystem-backed pages, the tail is | |
* required as the index of the page determines the key. For | |
* base pages, there is no tail page and tail == page. | |
*/ | |
tail = page; | |
page = compound_head(page); | |
mapping = READ_ONCE(page->mapping); | |
/* | |
* If page->mapping is NULL, then it cannot be a PageAnon | |
* page; but it might be the ZERO_PAGE or in the gate area or | |
* in a special mapping (all cases which we are happy to fail); | |
* or it may have been a good file page when get_user_pages_fast | |
* found it, but truncated or holepunched or subjected to | |
* invalidate_complete_page2 before we got the page lock (also | |
* cases which we are happy to fail). And we hold a reference, | |
* so refcount care in invalidate_complete_page's remove_mapping | |
* prevents drop_caches from setting mapping to NULL beneath us. | |
* | |
* The case we do have to guard against is when memory pressure made | |
* shmem_writepage move it from filecache to swapcache beneath us: | |
* an unlikely race, but we do need to retry for page->mapping. | |
*/ | |
if (unlikely(!mapping)) { | |
int shmem_swizzled; | |
/* | |
* Page lock is required to identify which special case above | |
* applies. If this is really a shmem page then the page lock | |
* will prevent unexpected transitions. | |
*/ | |
lock_page(page); | |
shmem_swizzled = PageSwapCache(page) || page->mapping; | |
unlock_page(page); | |
put_page(page); | |
if (shmem_swizzled) | |
goto again; | |
return -EFAULT; | |
} | |
/* | |
* Private mappings are handled in a simple way. | |
* | |
* If the futex key is stored on an anonymous page, then the associated | |
* object is the mm which is implicitly pinned by the calling process. | |
* | |
* NOTE: When userspace waits on a MAP_SHARED mapping, even if | |
* it's a read-only handle, it's expected that futexes attach to | |
* the object not the particular process. | |
*/ | |
if (PageAnon(page)) { | |
/* | |
* A RO anonymous page will never change and thus doesn't make | |
* sense for futex operations. | |
*/ | |
if (unlikely(should_fail_futex(true)) || ro) { | |
err = -EFAULT; | |
goto out; | |
} | |
key->both.offset |= FUT_OFF_MMSHARED; /* ref taken on mm */ | |
key->private.mm = mm; | |
key->private.address = address; | |
} else { | |
struct inode *inode; | |
/* | |
* The associated futex object in this case is the inode and | |
* the page->mapping must be traversed. Ordinarily this should | |
* be stabilised under page lock but it's not strictly | |
* necessary in this case as we just want to pin the inode, not | |
* update the radix tree or anything like that. | |
* | |
* The RCU read lock is taken as the inode is finally freed | |
* under RCU. If the mapping still matches expectations then the | |
* mapping->host can be safely accessed as being a valid inode. | |
*/ | |
rcu_read_lock(); | |
if (READ_ONCE(page->mapping) != mapping) { | |
rcu_read_unlock(); | |
put_page(page); | |
goto again; | |
} | |
inode = READ_ONCE(mapping->host); | |
if (!inode) { | |
rcu_read_unlock(); | |
put_page(page); | |
goto again; | |
} | |
key->both.offset |= FUT_OFF_INODE; /* inode-based key */ | |
key->shared.i_seq = get_inode_sequence_number(inode); | |
key->shared.pgoff = basepage_index(tail); | |
rcu_read_unlock(); | |
} | |
out: | |
put_page(page); | |
return err; | |
} | |
/** | |
* fault_in_user_writeable() - Fault in user address and verify RW access | |
* @uaddr: pointer to faulting user space address | |
* | |
* Slow path to fixup the fault we just took in the atomic write | |
* access to @uaddr. | |
* | |
* We have no generic implementation of a non-destructive write to the | |
* user address. We know that we faulted in the atomic pagefault | |
* disabled section so we can as well avoid the #PF overhead by | |
* calling get_user_pages() right away. | |
*/ | |
static int fault_in_user_writeable(u32 __user *uaddr) | |
{ | |
struct mm_struct *mm = current->mm; | |
int ret; | |
mmap_read_lock(mm); | |
ret = fixup_user_fault(mm, (unsigned long)uaddr, | |
FAULT_FLAG_WRITE, NULL); | |
mmap_read_unlock(mm); | |
return ret < 0 ? ret : 0; | |
} | |
/** | |
* futex_top_waiter() - Return the highest priority waiter on a futex | |
* @hb: the hash bucket the futex_q's reside in | |
* @key: the futex key (to distinguish it from other futex futex_q's) | |
* | |
* Must be called with the hb lock held. | |
*/ | |
static struct futex_q *futex_top_waiter(struct futex_hash_bucket *hb, | |
union futex_key *key) | |
{ | |
struct futex_q *this; | |
plist_for_each_entry(this, &hb->chain, list) { | |
if (match_futex(&this->key, key)) | |
return this; | |
} | |
return NULL; | |
} | |
static int cmpxchg_futex_value_locked(u32 *curval, u32 __user *uaddr, | |
u32 uval, u32 newval) | |
{ | |
int ret; | |
pagefault_disable(); | |
ret = futex_atomic_cmpxchg_inatomic(curval, uaddr, uval, newval); | |
pagefault_enable(); | |
return ret; | |
} | |
static int get_futex_value_locked(u32 *dest, u32 __user *from) | |
{ | |
int ret; | |
pagefault_disable(); | |
ret = __get_user(*dest, from); | |
pagefault_enable(); | |
return ret ? -EFAULT : 0; | |
} | |
/* | |
* PI code: | |
*/ | |
static int refill_pi_state_cache(void) | |
{ | |
struct futex_pi_state *pi_state; | |
if (likely(current->pi_state_cache)) | |
return 0; | |
pi_state = kzalloc(sizeof(*pi_state), GFP_KERNEL); | |
if (!pi_state) | |
return -ENOMEM; | |
INIT_LIST_HEAD(&pi_state->list); | |
/* pi_mutex gets initialized later */ | |
pi_state->owner = NULL; | |
refcount_set(&pi_state->refcount, 1); | |
pi_state->key = FUTEX_KEY_INIT; | |
current->pi_state_cache = pi_state; | |
return 0; | |
} | |
static struct futex_pi_state *alloc_pi_state(void) | |
{ | |
struct futex_pi_state *pi_state = current->pi_state_cache; | |
WARN_ON(!pi_state); | |
current->pi_state_cache = NULL; | |
return pi_state; | |
} | |
static void get_pi_state(struct futex_pi_state *pi_state) | |
{ | |
WARN_ON_ONCE(!refcount_inc_not_zero(&pi_state->refcount)); | |
} | |
/* | |
* Drops a reference to the pi_state object and frees or caches it | |
* when the last reference is gone. | |
*/ | |
static void put_pi_state(struct futex_pi_state *pi_state) | |
{ | |
if (!pi_state) | |
return; | |
if (!refcount_dec_and_test(&pi_state->refcount)) | |
return; | |
/* | |
* If pi_state->owner is NULL, the owner is most probably dying | |
* and has cleaned up the pi_state already | |
*/ | |
if (pi_state->owner) { | |
struct task_struct *owner; | |
unsigned long flags; | |
raw_spin_lock_irqsave(&pi_state->pi_mutex.wait_lock, flags); | |
owner = pi_state->owner; | |
if (owner) { | |
raw_spin_lock(&owner->pi_lock); | |
list_del_init(&pi_state->list); | |
raw_spin_unlock(&owner->pi_lock); | |
} | |
rt_mutex_proxy_unlock(&pi_state->pi_mutex, owner); | |
raw_spin_unlock_irqrestore(&pi_state->pi_mutex.wait_lock, flags); | |
} | |
if (current->pi_state_cache) { | |
kfree(pi_state); | |
} else { | |
/* | |
* pi_state->list is already empty. | |
* clear pi_state->owner. | |
* refcount is at 0 - put it back to 1. | |
*/ | |
pi_state->owner = NULL; | |
refcount_set(&pi_state->refcount, 1); | |
current->pi_state_cache = pi_state; | |
} | |
} | |
#ifdef CONFIG_FUTEX_PI | |
/* | |
* This task is holding PI mutexes at exit time => bad. | |
* Kernel cleans up PI-state, but userspace is likely hosed. | |
* (Robust-futex cleanup is separate and might save the day for userspace.) | |
*/ | |
static void exit_pi_state_list(struct task_struct *curr) | |
{ | |
struct list_head *next, *head = &curr->pi_state_list; | |
struct futex_pi_state *pi_state; | |
struct futex_hash_bucket *hb; | |
union futex_key key = FUTEX_KEY_INIT; | |
if (!futex_cmpxchg_enabled) | |
return; | |
/* | |
* We are a ZOMBIE and nobody can enqueue itself on | |
* pi_state_list anymore, but we have to be careful | |
* versus waiters unqueueing themselves: | |
*/ | |
raw_spin_lock_irq(&curr->pi_lock); | |
while (!list_empty(head)) { | |
next = head->next; | |
pi_state = list_entry(next, struct futex_pi_state, list); | |
key = pi_state->key; | |
hb = hash_futex(&key); | |
/* | |
* We can race against put_pi_state() removing itself from the | |
* list (a waiter going away). put_pi_state() will first | |
* decrement the reference count and then modify the list, so | |
* its possible to see the list entry but fail this reference | |
* acquire. | |
* | |
* In that case; drop the locks to let put_pi_state() make | |
* progress and retry the loop. | |
*/ | |
if (!refcount_inc_not_zero(&pi_state->refcount)) { | |
raw_spin_unlock_irq(&curr->pi_lock); | |
cpu_relax(); | |
raw_spin_lock_irq(&curr->pi_lock); | |
continue; | |
} | |
raw_spin_unlock_irq(&curr->pi_lock); | |
spin_lock(&hb->lock); | |
raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock); | |
raw_spin_lock(&curr->pi_lock); | |
/* | |
* We dropped the pi-lock, so re-check whether this | |
* task still owns the PI-state: | |
*/ | |
if (head->next != next) { | |
/* retain curr->pi_lock for the loop invariant */ | |
raw_spin_unlock(&pi_state->pi_mutex.wait_lock); | |
spin_unlock(&hb->lock); | |
put_pi_state(pi_state); | |
continue; | |
} | |
WARN_ON(pi_state->owner != curr); | |
WARN_ON(list_empty(&pi_state->list)); | |
list_del_init(&pi_state->list); | |
pi_state->owner = NULL; | |
raw_spin_unlock(&curr->pi_lock); | |
raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock); | |
spin_unlock(&hb->lock); | |
rt_mutex_futex_unlock(&pi_state->pi_mutex); | |
put_pi_state(pi_state); | |
raw_spin_lock_irq(&curr->pi_lock); | |
} | |
raw_spin_unlock_irq(&curr->pi_lock); | |
} | |
#else | |
static inline void exit_pi_state_list(struct task_struct *curr) { } | |
#endif | |
/* | |
* We need to check the following states: | |
* | |
* Waiter | pi_state | pi->owner | uTID | uODIED | ? | |
* | |
* [1] NULL | --- | --- | 0 | 0/1 | Valid | |
* [2] NULL | --- | --- | >0 | 0/1 | Valid | |
* | |
* [3] Found | NULL | -- | Any | 0/1 | Invalid | |
* | |
* [4] Found | Found | NULL | 0 | 1 | Valid | |
* [5] Found | Found | NULL | >0 | 1 | Invalid | |
* | |
* [6] Found | Found | task | 0 | 1 | Valid | |
* | |
* [7] Found | Found | NULL | Any | 0 | Invalid | |
* | |
* [8] Found | Found | task | ==taskTID | 0/1 | Valid | |
* [9] Found | Found | task | 0 | 0 | Invalid | |
* [10] Found | Found | task | !=taskTID | 0/1 | Invalid | |
* | |
* [1] Indicates that the kernel can acquire the futex atomically. We | |
* came here due to a stale FUTEX_WAITERS/FUTEX_OWNER_DIED bit. | |
* | |
* [2] Valid, if TID does not belong to a kernel thread. If no matching | |
* thread is found then it indicates that the owner TID has died. | |
* | |
* [3] Invalid. The waiter is queued on a non PI futex | |
* | |
* [4] Valid state after exit_robust_list(), which sets the user space | |
* value to FUTEX_WAITERS | FUTEX_OWNER_DIED. | |
* | |
* [5] The user space value got manipulated between exit_robust_list() | |
* and exit_pi_state_list() | |
* | |
* [6] Valid state after exit_pi_state_list() which sets the new owner in | |
* the pi_state but cannot access the user space value. | |
* | |
* [7] pi_state->owner can only be NULL when the OWNER_DIED bit is set. | |
* | |
* [8] Owner and user space value match | |
* | |
* [9] There is no transient state which sets the user space TID to 0 | |
* except exit_robust_list(), but this is indicated by the | |
* FUTEX_OWNER_DIED bit. See [4] | |
* | |
* [10] There is no transient state which leaves owner and user space | |
* TID out of sync. | |
* | |
* | |
* Serialization and lifetime rules: | |
* | |
* hb->lock: | |
* | |
* hb -> futex_q, relation | |
* futex_q -> pi_state, relation | |
* | |
* (cannot be raw because hb can contain arbitrary amount | |
* of futex_q's) | |
* | |
* pi_mutex->wait_lock: | |
* | |
* {uval, pi_state} | |
* | |
* (and pi_mutex 'obviously') | |
* | |
* p->pi_lock: | |
* | |
* p->pi_state_list -> pi_state->list, relation | |
* | |
* pi_state->refcount: | |
* | |
* pi_state lifetime | |
* | |
* | |
* Lock order: | |
* | |
* hb->lock | |
* pi_mutex->wait_lock | |
* p->pi_lock | |
* | |
*/ | |
/* | |
* Validate that the existing waiter has a pi_state and sanity check | |
* the pi_state against the user space value. If correct, attach to | |
* it. | |
*/ | |
static int attach_to_pi_state(u32 __user *uaddr, u32 uval, | |
struct futex_pi_state *pi_state, | |
struct futex_pi_state **ps) | |
{ | |
pid_t pid = uval & FUTEX_TID_MASK; | |
u32 uval2; | |
int ret; | |
/* | |
* Userspace might have messed up non-PI and PI futexes [3] | |
*/ | |
if (unlikely(!pi_state)) | |
return -EINVAL; | |
/* | |
* We get here with hb->lock held, and having found a | |
* futex_top_waiter(). This means that futex_lock_pi() of said futex_q | |
* has dropped the hb->lock in between queue_me() and unqueue_me_pi(), | |
* which in turn means that futex_lock_pi() still has a reference on | |
* our pi_state. | |
* | |
* The waiter holding a reference on @pi_state also protects against | |
* the unlocked put_pi_state() in futex_unlock_pi(), futex_lock_pi() | |
* and futex_wait_requeue_pi() as it cannot go to 0 and consequently | |
* free pi_state before we can take a reference ourselves. | |
*/ | |
WARN_ON(!refcount_read(&pi_state->refcount)); | |
/* | |
* Now that we have a pi_state, we can acquire wait_lock | |
* and do the state validation. | |
*/ | |
raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock); | |
/* | |
* Since {uval, pi_state} is serialized by wait_lock, and our current | |
* uval was read without holding it, it can have changed. Verify it | |
* still is what we expect it to be, otherwise retry the entire | |
* operation. | |
*/ | |
if (get_futex_value_locked(&uval2, uaddr)) | |
goto out_efault; | |
if (uval != uval2) | |
goto out_eagain; | |
/* | |
* Handle the owner died case: | |
*/ | |
if (uval & FUTEX_OWNER_DIED) { | |
/* | |
* exit_pi_state_list sets owner to NULL and wakes the | |
* topmost waiter. The task which acquires the | |
* pi_state->rt_mutex will fixup owner. | |
*/ | |
if (!pi_state->owner) { | |
/* | |
* No pi state owner, but the user space TID | |
* is not 0. Inconsistent state. [5] | |
*/ | |
if (pid) | |
goto out_einval; | |
/* | |
* Take a ref on the state and return success. [4] | |
*/ | |
goto out_attach; | |
} | |
/* | |
* If TID is 0, then either the dying owner has not | |
* yet executed exit_pi_state_list() or some waiter | |
* acquired the rtmutex in the pi state, but did not | |
* yet fixup the TID in user space. | |
* | |
* Take a ref on the state and return success. [6] | |
*/ | |
if (!pid) | |
goto out_attach; | |
} else { | |
/* | |
* If the owner died bit is not set, then the pi_state | |
* must have an owner. [7] | |
*/ | |
if (!pi_state->owner) | |
goto out_einval; | |
} | |
/* | |
* Bail out if user space manipulated the futex value. If pi | |
* state exists then the owner TID must be the same as the | |
* user space TID. [9/10] | |
*/ | |
if (pid != task_pid_vnr(pi_state->owner)) | |
goto out_einval; | |
out_attach: | |
get_pi_state(pi_state); | |
raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock); | |
*ps = pi_state; | |
return 0; | |
out_einval: | |
ret = -EINVAL; | |
goto out_error; | |
out_eagain: | |
ret = -EAGAIN; | |
goto out_error; | |
out_efault: | |
ret = -EFAULT; | |
goto out_error; | |
out_error: | |
raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock); | |
return ret; | |
} | |
/** | |
* wait_for_owner_exiting - Block until the owner has exited | |
* @ret: owner's current futex lock status | |
* @exiting: Pointer to the exiting task | |
* | |
* Caller must hold a refcount on @exiting. | |
*/ | |
static void wait_for_owner_exiting(int ret, struct task_struct *exiting) | |
{ | |
if (ret != -EBUSY) { | |
WARN_ON_ONCE(exiting); | |
return; | |
} | |
if (WARN_ON_ONCE(ret == -EBUSY && !exiting)) | |
return; | |
mutex_lock(&exiting->futex_exit_mutex); | |
/* | |
* No point in doing state checking here. If the waiter got here | |
* while the task was in exec()->exec_futex_release() then it can | |
* have any FUTEX_STATE_* value when the waiter has acquired the | |
* mutex. OK, if running, EXITING or DEAD if it reached exit() | |
* already. Highly unlikely and not a problem. Just one more round | |
* through the futex maze. | |
*/ | |
mutex_unlock(&exiting->futex_exit_mutex); | |
put_task_struct(exiting); | |
} | |
static int handle_exit_race(u32 __user *uaddr, u32 uval, | |
struct task_struct *tsk) | |
{ | |
u32 uval2; | |
/* | |
* If the futex exit state is not yet FUTEX_STATE_DEAD, tell the | |
* caller that the alleged owner is busy. | |
*/ | |
if (tsk && tsk->futex_state != FUTEX_STATE_DEAD) | |
return -EBUSY; | |
/* | |
* Reread the user space value to handle the following situation: | |
* | |
* CPU0 CPU1 | |
* | |
* sys_exit() sys_futex() | |
* do_exit() futex_lock_pi() | |
* futex_lock_pi_atomic() | |
* exit_signals(tsk) No waiters: | |
* tsk->flags |= PF_EXITING; *uaddr == 0x00000PID | |
* mm_release(tsk) Set waiter bit | |
* exit_robust_list(tsk) { *uaddr = 0x80000PID; | |
* Set owner died attach_to_pi_owner() { | |
* *uaddr = 0xC0000000; tsk = get_task(PID); | |
* } if (!tsk->flags & PF_EXITING) { | |
* ... attach(); | |
* tsk->futex_state = } else { | |
* FUTEX_STATE_DEAD; if (tsk->futex_state != | |
* FUTEX_STATE_DEAD) | |
* return -EAGAIN; | |
* return -ESRCH; <--- FAIL | |
* } | |
* | |
* Returning ESRCH unconditionally is wrong here because the | |
* user space value has been changed by the exiting task. | |
* | |
* The same logic applies to the case where the exiting task is | |
* already gone. | |
*/ | |
if (get_futex_value_locked(&uval2, uaddr)) | |
return -EFAULT; | |
/* If the user space value has changed, try again. */ | |
if (uval2 != uval) | |
return -EAGAIN; | |
/* | |
* The exiting task did not have a robust list, the robust list was | |
* corrupted or the user space value in *uaddr is simply bogus. | |
* Give up and tell user space. | |
*/ | |
return -ESRCH; | |
} | |
/* | |
* Lookup the task for the TID provided from user space and attach to | |
* it after doing proper sanity checks. | |
*/ | |
static int attach_to_pi_owner(u32 __user *uaddr, u32 uval, union futex_key *key, | |
struct futex_pi_state **ps, | |
struct task_struct **exiting) | |
{ | |
pid_t pid = uval & FUTEX_TID_MASK; | |
struct futex_pi_state *pi_state; | |
struct task_struct *p; | |
/* | |
* We are the first waiter - try to look up the real owner and attach | |
* the new pi_state to it, but bail out when TID = 0 [1] | |
* | |
* The !pid check is paranoid. None of the call sites should end up | |
* with pid == 0, but better safe than sorry. Let the caller retry | |
*/ | |
if (!pid) | |
return -EAGAIN; | |
p = find_get_task_by_vpid(pid); | |
if (!p) | |
return handle_exit_race(uaddr, uval, NULL); | |
if (unlikely(p->flags & PF_KTHREAD)) { | |
put_task_struct(p); | |
return -EPERM; | |
} | |
/* | |
* We need to look at the task state to figure out, whether the | |
* task is exiting. To protect against the change of the task state | |
* in futex_exit_release(), we do this protected by p->pi_lock: | |
*/ | |
raw_spin_lock_irq(&p->pi_lock); | |
if (unlikely(p->futex_state != FUTEX_STATE_OK)) { | |
/* | |
* The task is on the way out. When the futex state is | |
* FUTEX_STATE_DEAD, we know that the task has finished | |
* the cleanup: | |
*/ | |
int ret = handle_exit_race(uaddr, uval, p); | |
raw_spin_unlock_irq(&p->pi_lock); | |
/* | |
* If the owner task is between FUTEX_STATE_EXITING and | |
* FUTEX_STATE_DEAD then store the task pointer and keep | |
* the reference on the task struct. The calling code will | |
* drop all locks, wait for the task to reach | |
* FUTEX_STATE_DEAD and then drop the refcount. This is | |
* required to prevent a live lock when the current task | |
* preempted the exiting task between the two states. | |
*/ | |
if (ret == -EBUSY) | |
*exiting = p; | |
else | |
put_task_struct(p); | |
return ret; | |
} | |
/* | |
* No existing pi state. First waiter. [2] | |
* | |
* This creates pi_state, we have hb->lock held, this means nothing can | |
* observe this state, wait_lock is irrelevant. | |
*/ | |
pi_state = alloc_pi_state(); | |
/* | |
* Initialize the pi_mutex in locked state and make @p | |
* the owner of it: | |
*/ | |
rt_mutex_init_proxy_locked(&pi_state->pi_mutex, p); | |
/* Store the key for possible exit cleanups: */ | |
pi_state->key = *key; | |
WARN_ON(!list_empty(&pi_state->list)); | |
list_add(&pi_state->list, &p->pi_state_list); | |
/* | |
* Assignment without holding pi_state->pi_mutex.wait_lock is safe | |
* because there is no concurrency as the object is not published yet. | |
*/ | |
pi_state->owner = p; | |
raw_spin_unlock_irq(&p->pi_lock); | |
put_task_struct(p); | |
*ps = pi_state; | |
return 0; | |
} | |
static int lookup_pi_state(u32 __user *uaddr, u32 uval, | |
struct futex_hash_bucket *hb, | |
union futex_key *key, struct futex_pi_state **ps, | |
struct task_struct **exiting) | |
{ | |
struct futex_q *top_waiter = futex_top_waiter(hb, key); | |
/* | |
* If there is a waiter on that futex, validate it and | |
* attach to the pi_state when the validation succeeds. | |
*/ | |
if (top_waiter) | |
return attach_to_pi_state(uaddr, uval, top_waiter->pi_state, ps); | |
/* | |
* We are the first waiter - try to look up the owner based on | |
* @uval and attach to it. | |
*/ | |
return attach_to_pi_owner(uaddr, uval, key, ps, exiting); | |
} | |
static int lock_pi_update_atomic(u32 __user *uaddr, u32 uval, u32 newval) | |
{ | |
int err; | |
u32 curval; | |
if (unlikely(should_fail_futex(true))) | |
return -EFAULT; | |
err = cmpxchg_futex_value_locked(&curval, uaddr, uval, newval); | |
if (unlikely(err)) | |
return err; | |
/* If user space value changed, let the caller retry */ | |
return curval != uval ? -EAGAIN : 0; | |
} | |
/** | |
* futex_lock_pi_atomic() - Atomic work required to acquire a pi aware futex | |
* @uaddr: the pi futex user address | |
* @hb: the pi futex hash bucket | |
* @key: the futex key associated with uaddr and hb | |
* @ps: the pi_state pointer where we store the result of the | |
* lookup | |
* @task: the task to perform the atomic lock work for. This will | |
* be "current" except in the case of requeue pi. | |
* @exiting: Pointer to store the task pointer of the owner task | |
* which is in the middle of exiting | |
* @set_waiters: force setting the FUTEX_WAITERS bit (1) or not (0) | |
* | |
* Return: | |
* - 0 - ready to wait; | |
* - 1 - acquired the lock; | |
* - <0 - error | |
* | |
* The hb->lock and futex_key refs shall be held by the caller. | |
* | |
* @exiting is only set when the return value is -EBUSY. If so, this holds | |
* a refcount on the exiting task on return and the caller needs to drop it | |
* after waiting for the exit to complete. | |
*/ | |
static int futex_lock_pi_atomic(u32 __user *uaddr, struct futex_hash_bucket *hb, | |
union futex_key *key, | |
struct futex_pi_state **ps, | |
struct task_struct *task, | |
struct task_struct **exiting, | |
int set_waiters) | |
{ | |
u32 uval, newval, vpid = task_pid_vnr(task); | |
struct futex_q *top_waiter; | |
int ret; | |
/* | |
* Read the user space value first so we can validate a few | |
* things before proceeding further. | |
*/ | |
if (get_futex_value_locked(&uval, uaddr)) | |
return -EFAULT; | |
if (unlikely(should_fail_futex(true))) | |
return -EFAULT; | |
/* | |
* Detect deadlocks. | |
*/ | |
if ((unlikely((uval & FUTEX_TID_MASK) == vpid))) | |
return -EDEADLK; | |
if ((unlikely(should_fail_futex(true)))) | |
return -EDEADLK; | |
/* | |
* Lookup existing state first. If it exists, try to attach to | |
* its pi_state. | |
*/ | |
top_waiter = futex_top_waiter(hb, key); | |
if (top_waiter) | |
return attach_to_pi_state(uaddr, uval, top_waiter->pi_state, ps); | |
/* | |
* No waiter and user TID is 0. We are here because the | |
* waiters or the owner died bit is set or called from | |
* requeue_cmp_pi or for whatever reason something took the | |
* syscall. | |
*/ | |
if (!(uval & FUTEX_TID_MASK)) { | |
/* | |
* We take over the futex. No other waiters and the user space | |
* TID is 0. We preserve the owner died bit. | |
*/ | |
newval = uval & FUTEX_OWNER_DIED; | |
newval |= vpid; | |
/* The futex requeue_pi code can enforce the waiters bit */ | |
if (set_waiters) | |
newval |= FUTEX_WAITERS; | |
ret = lock_pi_update_atomic(uaddr, uval, newval); | |
/* If the take over worked, return 1 */ | |
return ret < 0 ? ret : 1; | |
} | |
/* | |
* First waiter. Set the waiters bit before attaching ourself to | |
* the owner. If owner tries to unlock, it will be forced into | |
* the kernel and blocked on hb->lock. | |
*/ | |
newval = uval | FUTEX_WAITERS; | |
ret = lock_pi_update_atomic(uaddr, uval, newval); | |
if (ret) | |
return ret; | |
/* | |
* If the update of the user space value succeeded, we try to | |
* attach to the owner. If that fails, no harm done, we only | |
* set the FUTEX_WAITERS bit in the user space variable. | |
*/ | |
return attach_to_pi_owner(uaddr, newval, key, ps, exiting); | |
} | |
/** | |
* __unqueue_futex() - Remove the futex_q from its futex_hash_bucket | |
* @q: The futex_q to unqueue | |
* | |
* The q->lock_ptr must not be NULL and must be held by the caller. | |
*/ | |
static void __unqueue_futex(struct futex_q *q) | |
{ | |
struct futex_hash_bucket *hb; | |
if (WARN_ON_SMP(!q->lock_ptr) || WARN_ON(plist_node_empty(&q->list))) | |
return; | |
lockdep_assert_held(q->lock_ptr); | |
hb = container_of(q->lock_ptr, struct futex_hash_bucket, lock); | |
plist_del(&q->list, &hb->chain); | |
hb_waiters_dec(hb); | |
} | |
/* | |
* The hash bucket lock must be held when this is called. | |
* Afterwards, the futex_q must not be accessed. Callers | |
* must ensure to later call wake_up_q() for the actual | |
* wakeups to occur. | |
*/ | |
static void mark_wake_futex(struct wake_q_head *wake_q, struct futex_q *q) | |
{ | |
struct task_struct *p = q->task; | |
if (WARN(q->pi_state || q->rt_waiter, "refusing to wake PI futex\n")) | |
return; | |
get_task_struct(p); | |
__unqueue_futex(q); | |
/* | |
* The waiting task can free the futex_q as soon as q->lock_ptr = NULL | |
* is written, without taking any locks. This is possible in the event | |
* of a spurious wakeup, for example. A memory barrier is required here | |
* to prevent the following store to lock_ptr from getting ahead of the | |
* plist_del in __unqueue_futex(). | |
*/ | |
smp_store_release(&q->lock_ptr, NULL); | |
/* | |
* Queue the task for later wakeup for after we've released | |
* the hb->lock. | |
*/ | |
wake_q_add_safe(wake_q, p); | |
} | |
/* | |
* Caller must hold a reference on @pi_state. | |
*/ | |
static int wake_futex_pi(u32 __user *uaddr, u32 uval, struct futex_pi_state *pi_state) | |
{ | |
u32 curval, newval; | |
struct task_struct *new_owner; | |
bool postunlock = false; | |
DEFINE_WAKE_Q(wake_q); | |
int ret = 0; | |
new_owner = rt_mutex_next_owner(&pi_state->pi_mutex); | |
if (WARN_ON_ONCE(!new_owner)) { | |
/* | |
* As per the comment in futex_unlock_pi() this should not happen. | |
* | |
* When this happens, give up our locks and try again, giving | |
* the futex_lock_pi() instance time to complete, either by | |
* waiting on the rtmutex or removing itself from the futex | |
* queue. | |
*/ | |
ret = -EAGAIN; | |
goto out_unlock; | |
} | |
/* | |
* We pass it to the next owner. The WAITERS bit is always kept | |
* enabled while there is PI state around. We cleanup the owner | |
* died bit, because we are the owner. | |
*/ | |
newval = FUTEX_WAITERS | task_pid_vnr(new_owner); | |
if (unlikely(should_fail_futex(true))) { | |
ret = -EFAULT; | |
goto out_unlock; | |
} | |
ret = cmpxchg_futex_value_locked(&curval, uaddr, uval, newval); | |
if (!ret && (curval != uval)) { | |
/* | |
* If a unconditional UNLOCK_PI operation (user space did not | |
* try the TID->0 transition) raced with a waiter setting the | |
* FUTEX_WAITERS flag between get_user() and locking the hash | |
* bucket lock, retry the operation. | |
*/ | |
if ((FUTEX_TID_MASK & curval) == uval) | |
ret = -EAGAIN; | |
else | |
ret = -EINVAL; | |
} | |
if (ret) | |
goto out_unlock; | |
/* | |
* This is a point of no return; once we modify the uval there is no | |
* going back and subsequent operations must not fail. | |
*/ | |
raw_spin_lock(&pi_state->owner->pi_lock); | |
WARN_ON(list_empty(&pi_state->list)); | |
list_del_init(&pi_state->list); | |
raw_spin_unlock(&pi_state->owner->pi_lock); | |
raw_spin_lock(&new_owner->pi_lock); | |
WARN_ON(!list_empty(&pi_state->list)); | |
list_add(&pi_state->list, &new_owner->pi_state_list); | |
pi_state->owner = new_owner; | |
raw_spin_unlock(&new_owner->pi_lock); | |
postunlock = __rt_mutex_futex_unlock(&pi_state->pi_mutex, &wake_q); | |
out_unlock: | |
raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock); | |
if (postunlock) | |
rt_mutex_postunlock(&wake_q); | |
return ret; | |
} | |
/* | |
* Express the locking dependencies for lockdep: | |
*/ | |
static inline void | |
double_lock_hb(struct futex_hash_bucket *hb1, struct futex_hash_bucket *hb2) | |
{ | |
if (hb1 <= hb2) { | |
spin_lock(&hb1->lock); | |
if (hb1 < hb2) | |
spin_lock_nested(&hb2->lock, SINGLE_DEPTH_NESTING); | |
} else { /* hb1 > hb2 */ | |
spin_lock(&hb2->lock); | |
spin_lock_nested(&hb1->lock, SINGLE_DEPTH_NESTING); | |
} | |
} | |
static inline void | |
double_unlock_hb(struct futex_hash_bucket *hb1, struct futex_hash_bucket *hb2) | |
{ | |
spin_unlock(&hb1->lock); | |
if (hb1 != hb2) | |
spin_unlock(&hb2->lock); | |
} | |
/* | |
* Wake up waiters matching bitset queued on this futex (uaddr). | |
*/ | |
static int | |
futex_wake(u32 __user *uaddr, unsigned int flags, int nr_wake, u32 bitset) | |
{ | |
struct futex_hash_bucket *hb; | |
struct futex_q *this, *next; | |
union futex_key key = FUTEX_KEY_INIT; | |
int ret; | |
DEFINE_WAKE_Q(wake_q); | |
if (!bitset) | |
return -EINVAL; | |
ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &key, FUTEX_READ); | |
if (unlikely(ret != 0)) | |
return ret; | |
hb = hash_futex(&key); | |
/* Make sure we really have tasks to wakeup */ | |
if (!hb_waiters_pending(hb)) | |
return ret; | |
spin_lock(&hb->lock); | |
plist_for_each_entry_safe(this, next, &hb->chain, list) { | |
if (match_futex (&this->key, &key)) { | |
if (this->pi_state || this->rt_waiter) { | |
ret = -EINVAL; | |
break; | |
} | |
/* Check if one of the bits is set in both bitsets */ | |
if (!(this->bitset & bitset)) | |
continue; | |
mark_wake_futex(&wake_q, this); | |
if (++ret >= nr_wake) | |
break; | |
} | |
} | |
spin_unlock(&hb->lock); | |
wake_up_q(&wake_q); | |
return ret; | |
} | |
static int futex_atomic_op_inuser(unsigned int encoded_op, u32 __user *uaddr) | |
{ | |
unsigned int op = (encoded_op & 0x70000000) >> 28; | |
unsigned int cmp = (encoded_op & 0x0f000000) >> 24; | |
int oparg = sign_extend32((encoded_op & 0x00fff000) >> 12, 11); | |
int cmparg = sign_extend32(encoded_op & 0x00000fff, 11); | |
int oldval, ret; | |
if (encoded_op & (FUTEX_OP_OPARG_SHIFT << 28)) { | |
if (oparg < 0 || oparg > 31) { | |
char comm[sizeof(current->comm)]; | |
/* | |
* kill this print and return -EINVAL when userspace | |
* is sane again | |
*/ | |
pr_info_ratelimited("futex_wake_op: %s tries to shift op by %d; fix this program\n", | |
get_task_comm(comm, current), oparg); | |
oparg &= 31; | |
} | |
oparg = 1 << oparg; | |
} | |
pagefault_disable(); | |
ret = arch_futex_atomic_op_inuser(op, oparg, &oldval, uaddr); | |
pagefault_enable(); | |
if (ret) | |
return ret; | |
switch (cmp) { | |
case FUTEX_OP_CMP_EQ: | |
return oldval == cmparg; | |
case FUTEX_OP_CMP_NE: | |
return oldval != cmparg; | |
case FUTEX_OP_CMP_LT: | |
return oldval < cmparg; | |
case FUTEX_OP_CMP_GE: | |
return oldval >= cmparg; | |
case FUTEX_OP_CMP_LE: | |
return oldval <= cmparg; | |
case FUTEX_OP_CMP_GT: | |
return oldval > cmparg; | |
default: | |
return -ENOSYS; | |
} | |
} | |
/* | |
* Wake up all waiters hashed on the physical page that is mapped | |
* to this virtual address: | |
*/ | |
static int | |
futex_wake_op(u32 __user *uaddr1, unsigned int flags, u32 __user *uaddr2, | |
int nr_wake, int nr_wake2, int op) | |
{ | |
union futex_key key1 = FUTEX_KEY_INIT, key2 = FUTEX_KEY_INIT; | |
struct futex_hash_bucket *hb1, *hb2; | |
struct futex_q *this, *next; | |
int ret, op_ret; | |
DEFINE_WAKE_Q(wake_q); | |
retry: | |
ret = get_futex_key(uaddr1, flags & FLAGS_SHARED, &key1, FUTEX_READ); | |
if (unlikely(ret != 0)) | |
return ret; | |
ret = get_futex_key(uaddr2, flags & FLAGS_SHARED, &key2, FUTEX_WRITE); | |
if (unlikely(ret != 0)) | |
return ret; | |
hb1 = hash_futex(&key1); | |
hb2 = hash_futex(&key2); | |
retry_private: | |
double_lock_hb(hb1, hb2); | |
op_ret = futex_atomic_op_inuser(op, uaddr2); | |
if (unlikely(op_ret < 0)) { | |
double_unlock_hb(hb1, hb2); | |
if (!IS_ENABLED(CONFIG_MMU) || | |
unlikely(op_ret != -EFAULT && op_ret != -EAGAIN)) { | |
/* | |
* we don't get EFAULT from MMU faults if we don't have | |
* an MMU, but we might get them from range checking | |
*/ | |
ret = op_ret; | |
return ret; | |
} | |
if (op_ret == -EFAULT) { | |
ret = fault_in_user_writeable(uaddr2); | |
if (ret) | |
return ret; | |
} | |
if (!(flags & FLAGS_SHARED)) { | |
cond_resched(); | |
goto retry_private; | |
} | |
cond_resched(); | |
goto retry; | |
} | |
plist_for_each_entry_safe(this, next, &hb1->chain, list) { | |
if (match_futex (&this->key, &key1)) { | |
if (this->pi_state || this->rt_waiter) { | |
ret = -EINVAL; | |
goto out_unlock; | |
} | |
mark_wake_futex(&wake_q, this); | |
if (++ret >= nr_wake) | |
break; | |
} | |
} | |
if (op_ret > 0) { | |
op_ret = 0; | |
plist_for_each_entry_safe(this, next, &hb2->chain, list) { | |
if (match_futex (&this->key, &key2)) { | |
if (this->pi_state || this->rt_waiter) { | |
ret = -EINVAL; | |
goto out_unlock; | |
} | |
mark_wake_futex(&wake_q, this); | |
if (++op_ret >= nr_wake2) | |
break; | |
} | |
} | |
ret += op_ret; | |
} | |
out_unlock: | |
double_unlock_hb(hb1, hb2); | |
wake_up_q(&wake_q); | |
return ret; | |
} | |
/** | |
* requeue_futex() - Requeue a futex_q from one hb to another | |
* @q: the futex_q to requeue | |
* @hb1: the source hash_bucket | |
* @hb2: the target hash_bucket | |
* @key2: the new key for the requeued futex_q | |
*/ | |
static inline | |
void requeue_futex(struct futex_q *q, struct futex_hash_bucket *hb1, | |
struct futex_hash_bucket *hb2, union futex_key *key2) | |
{ | |
/* | |
* If key1 and key2 hash to the same bucket, no need to | |
* requeue. | |
*/ | |
if (likely(&hb1->chain != &hb2->chain)) { | |
plist_del(&q->list, &hb1->chain); | |
hb_waiters_dec(hb1); | |
hb_waiters_inc(hb2); | |
plist_add(&q->list, &hb2->chain); | |
q->lock_ptr = &hb2->lock; | |
} | |
q->key = *key2; | |
} | |
/** | |
* requeue_pi_wake_futex() - Wake a task that acquired the lock during requeue | |
* @q: the futex_q | |
* @key: the key of the requeue target futex | |
* @hb: the hash_bucket of the requeue target futex | |
* | |
* During futex_requeue, with requeue_pi=1, it is possible to acquire the | |
* target futex if it is uncontended or via a lock steal. Set the futex_q key | |
* to the requeue target futex so the waiter can detect the wakeup on the right | |
* futex, but remove it from the hb and NULL the rt_waiter so it can detect | |
* atomic lock acquisition. Set the q->lock_ptr to the requeue target hb->lock | |
* to protect access to the pi_state to fixup the owner later. Must be called | |
* with both q->lock_ptr and hb->lock held. | |
*/ | |
static inline | |
void requeue_pi_wake_futex(struct futex_q *q, union futex_key *key, | |
struct futex_hash_bucket *hb) | |
{ | |
q->key = *key; | |
__unqueue_futex(q); | |
WARN_ON(!q->rt_waiter); | |
q->rt_waiter = NULL; | |
q->lock_ptr = &hb->lock; | |
wake_up_state(q->task, TASK_NORMAL); | |
} | |
/** | |
* futex_proxy_trylock_atomic() - Attempt an atomic lock for the top waiter | |
* @pifutex: the user address of the to futex | |
* @hb1: the from futex hash bucket, must be locked by the caller | |
* @hb2: the to futex hash bucket, must be locked by the caller | |
* @key1: the from futex key | |
* @key2: the to futex key | |
* @ps: address to store the pi_state pointer | |
* @exiting: Pointer to store the task pointer of the owner task | |
* which is in the middle of exiting | |
* @set_waiters: force setting the FUTEX_WAITERS bit (1) or not (0) | |
* | |
* Try and get the lock on behalf of the top waiter if we can do it atomically. | |
* Wake the top waiter if we succeed. If the caller specified set_waiters, | |
* then direct futex_lock_pi_atomic() to force setting the FUTEX_WAITERS bit. | |
* hb1 and hb2 must be held by the caller. | |
* | |
* @exiting is only set when the return value is -EBUSY. If so, this holds | |
* a refcount on the exiting task on return and the caller needs to drop it | |
* after waiting for the exit to complete. | |
* | |
* Return: | |
* - 0 - failed to acquire the lock atomically; | |
* - >0 - acquired the lock, return value is vpid of the top_waiter | |
* - <0 - error | |
*/ | |
static int | |
futex_proxy_trylock_atomic(u32 __user *pifutex, struct futex_hash_bucket *hb1, | |
struct futex_hash_bucket *hb2, union futex_key *key1, | |
union futex_key *key2, struct futex_pi_state **ps, | |
struct task_struct **exiting, int set_waiters) | |
{ | |
struct futex_q *top_waiter = NULL; | |
u32 curval; | |
int ret, vpid; | |
if (get_futex_value_locked(&curval, pifutex)) | |
return -EFAULT; | |
if (unlikely(should_fail_futex(true))) | |
return -EFAULT; | |
/* | |
* Find the top_waiter and determine if there are additional waiters. | |
* If the caller intends to requeue more than 1 waiter to pifutex, | |
* force futex_lock_pi_atomic() to set the FUTEX_WAITERS bit now, | |
* as we have means to handle the possible fault. If not, don't set | |
* the bit unecessarily as it will force the subsequent unlock to enter | |
* the kernel. | |
*/ | |
top_waiter = futex_top_waiter(hb1, key1); | |
/* There are no waiters, nothing for us to do. */ | |
if (!top_waiter) | |
return 0; | |
/* Ensure we requeue to the expected futex. */ | |
if (!match_futex(top_waiter->requeue_pi_key, key2)) | |
return -EINVAL; | |
/* | |
* Try to take the lock for top_waiter. Set the FUTEX_WAITERS bit in | |
* the contended case or if set_waiters is 1. The pi_state is returned | |
* in ps in contended cases. | |
*/ | |
vpid = task_pid_vnr(top_waiter->task); | |
ret = futex_lock_pi_atomic(pifutex, hb2, key2, ps, top_waiter->task, | |
exiting, set_waiters); | |
if (ret == 1) { | |
requeue_pi_wake_futex(top_waiter, key2, hb2); | |
return vpid; | |
} | |
return ret; | |
} | |
/** | |
* futex_requeue() - Requeue waiters from uaddr1 to uaddr2 | |
* @uaddr1: source futex user address | |
* @flags: futex flags (FLAGS_SHARED, etc.) | |
* @uaddr2: target futex user address | |
* @nr_wake: number of waiters to wake (must be 1 for requeue_pi) | |
* @nr_requeue: number of waiters to requeue (0-INT_MAX) | |
* @cmpval: @uaddr1 expected value (or %NULL) | |
* @requeue_pi: if we are attempting to requeue from a non-pi futex to a | |
* pi futex (pi to pi requeue is not supported) | |
* | |
* Requeue waiters on uaddr1 to uaddr2. In the requeue_pi case, try to acquire | |
* uaddr2 atomically on behalf of the top waiter. | |
* | |
* Return: | |
* - >=0 - on success, the number of tasks requeued or woken; | |
* - <0 - on error | |
*/ | |
static int futex_requeue(u32 __user *uaddr1, unsigned int flags, | |
u32 __user *uaddr2, int nr_wake, int nr_requeue, | |
u32 *cmpval, int requeue_pi) | |
{ | |
union futex_key key1 = FUTEX_KEY_INIT, key2 = FUTEX_KEY_INIT; | |
int task_count = 0, ret; | |
struct futex_pi_state *pi_state = NULL; | |
struct futex_hash_bucket *hb1, *hb2; | |
struct futex_q *this, *next; | |
DEFINE_WAKE_Q(wake_q); | |
if (nr_wake < 0 || nr_requeue < 0) | |
return -EINVAL; | |
/* | |
* When PI not supported: return -ENOSYS if requeue_pi is true, | |
* consequently the compiler knows requeue_pi is always false past | |
* this point which will optimize away all the conditional code | |
* further down. | |
*/ | |
if (!IS_ENABLED(CONFIG_FUTEX_PI) && requeue_pi) | |
return -ENOSYS; | |
if (requeue_pi) { | |
/* | |
* Requeue PI only works on two distinct uaddrs. This | |
* check is only valid for private futexes. See below. | |
*/ | |
if (uaddr1 == uaddr2) | |
return -EINVAL; | |
/* | |
* requeue_pi requires a pi_state, try to allocate it now | |
* without any locks in case it fails. | |
*/ | |
if (refill_pi_state_cache()) | |
return -ENOMEM; | |
/* | |
* requeue_pi must wake as many tasks as it can, up to nr_wake | |
* + nr_requeue, since it acquires the rt_mutex prior to | |
* returning to userspace, so as to not leave the rt_mutex with | |
* waiters and no owner. However, second and third wake-ups | |
* cannot be predicted as they involve race conditions with the | |
* first wake and a fault while looking up the pi_state. Both | |
* pthread_cond_signal() and pthread_cond_broadcast() should | |
* use nr_wake=1. | |
*/ | |
if (nr_wake != 1) | |
return -EINVAL; | |
} | |
retry: | |
ret = get_futex_key(uaddr1, flags & FLAGS_SHARED, &key1, FUTEX_READ); | |
if (unlikely(ret != 0)) | |
return ret; | |
ret = get_futex_key(uaddr2, flags & FLAGS_SHARED, &key2, | |
requeue_pi ? FUTEX_WRITE : FUTEX_READ); | |
if (unlikely(ret != 0)) | |
return ret; | |
/* | |
* The check above which compares uaddrs is not sufficient for | |
* shared futexes. We need to compare the keys: | |
*/ | |
if (requeue_pi && match_futex(&key1, &key2)) | |
return -EINVAL; | |
hb1 = hash_futex(&key1); | |
hb2 = hash_futex(&key2); | |
retry_private: | |
hb_waiters_inc(hb2); | |
double_lock_hb(hb1, hb2); | |
if (likely(cmpval != NULL)) { | |
u32 curval; | |
ret = get_futex_value_locked(&curval, uaddr1); | |
if (unlikely(ret)) { | |
double_unlock_hb(hb1, hb2); | |
hb_waiters_dec(hb2); | |
ret = get_user(curval, uaddr1); | |
if (ret) | |
return ret; | |
if (!(flags & FLAGS_SHARED)) | |
goto retry_private; | |
goto retry; | |
} | |
if (curval != *cmpval) { | |
ret = -EAGAIN; | |
goto out_unlock; | |
} | |
} | |
if (requeue_pi && (task_count - nr_wake < nr_requeue)) { | |
struct task_struct *exiting = NULL; | |
/* | |
* Attempt to acquire uaddr2 and wake the top waiter. If we | |
* intend to requeue waiters, force setting the FUTEX_WAITERS | |
* bit. We force this here where we are able to easily handle | |
* faults rather in the requeue loop below. | |
*/ | |
ret = futex_proxy_trylock_atomic(uaddr2, hb1, hb2, &key1, | |
&key2, &pi_state, | |
&exiting, nr_requeue); | |
/* | |
* At this point the top_waiter has either taken uaddr2 or is | |
* waiting on it. If the former, then the pi_state will not | |
* exist yet, look it up one more time to ensure we have a | |
* reference to it. If the lock was taken, ret contains the | |
* vpid of the top waiter task. | |
* If the lock was not taken, we have pi_state and an initial | |
* refcount on it. In case of an error we have nothing. | |
*/ | |
if (ret > 0) { | |
WARN_ON(pi_state); | |
task_count++; | |
/* | |
* If we acquired the lock, then the user space value | |
* of uaddr2 should be vpid. It cannot be changed by | |
* the top waiter as it is blocked on hb2 lock if it | |
* tries to do so. If something fiddled with it behind | |
* our back the pi state lookup might unearth it. So | |
* we rather use the known value than rereading and | |
* handing potential crap to lookup_pi_state. | |
* | |
* If that call succeeds then we have pi_state and an | |
* initial refcount on it. | |
*/ | |
ret = lookup_pi_state(uaddr2, ret, hb2, &key2, | |
&pi_state, &exiting); | |
} | |
switch (ret) { | |
case 0: | |
/* We hold a reference on the pi state. */ | |
break; | |
/* If the above failed, then pi_state is NULL */ | |
case -EFAULT: | |
double_unlock_hb(hb1, hb2); | |
hb_waiters_dec(hb2); | |
ret = fault_in_user_writeable(uaddr2); | |
if (!ret) | |
goto retry; | |
return ret; | |
case -EBUSY: | |
case -EAGAIN: | |
/* | |
* Two reasons for this: | |
* - EBUSY: Owner is exiting and we just wait for the | |
* exit to complete. | |
* - EAGAIN: The user space value changed. | |
*/ | |
double_unlock_hb(hb1, hb2); | |
hb_waiters_dec(hb2); | |
/* | |
* Handle the case where the owner is in the middle of | |
* exiting. Wait for the exit to complete otherwise | |
* this task might loop forever, aka. live lock. | |
*/ | |
wait_for_owner_exiting(ret, exiting); | |
cond_resched(); | |
goto retry; | |
default: | |
goto out_unlock; | |
} | |
} | |
plist_for_each_entry_safe(this, next, &hb1->chain, list) { | |
if (task_count - nr_wake >= nr_requeue) | |
break; | |
if (!match_futex(&this->key, &key1)) | |
continue; | |
/* | |
* FUTEX_WAIT_REQEUE_PI and FUTEX_CMP_REQUEUE_PI should always | |
* be paired with each other and no other futex ops. | |
* | |
* We should never be requeueing a futex_q with a pi_state, | |
* which is awaiting a futex_unlock_pi(). | |
*/ | |
if ((requeue_pi && !this->rt_waiter) || | |
(!requeue_pi && this->rt_waiter) || | |
this->pi_state) { | |
ret = -EINVAL; | |
break; | |
} | |
/* | |
* Wake nr_wake waiters. For requeue_pi, if we acquired the | |
* lock, we already woke the top_waiter. If not, it will be | |
* woken by futex_unlock_pi(). | |
*/ | |
if (++task_count <= nr_wake && !requeue_pi) { | |
mark_wake_futex(&wake_q, this); | |
continue; | |
} | |
/* Ensure we requeue to the expected futex for requeue_pi. */ | |
if (requeue_pi && !match_futex(this->requeue_pi_key, &key2)) { | |
ret = -EINVAL; | |
break; | |
} | |
/* | |
* Requeue nr_requeue waiters and possibly one more in the case | |
* of requeue_pi if we couldn't acquire the lock atomically. | |
*/ | |
if (requeue_pi) { | |
/* | |
* Prepare the waiter to take the rt_mutex. Take a | |
* refcount on the pi_state and store the pointer in | |
* the futex_q object of the waiter. | |
*/ | |
get_pi_state(pi_state); | |
this->pi_state = pi_state; | |
ret = rt_mutex_start_proxy_lock(&pi_state->pi_mutex, | |
this->rt_waiter, | |
this->task); | |
if (ret == 1) { | |
/* | |
* We got the lock. We do neither drop the | |
* refcount on pi_state nor clear | |
* this->pi_state because the waiter needs the | |
* pi_state for cleaning up the user space | |
* value. It will drop the refcount after | |
* doing so. | |
*/ | |
requeue_pi_wake_futex(this, &key2, hb2); | |
continue; | |
} else if (ret) { | |
/* | |
* rt_mutex_start_proxy_lock() detected a | |
* potential deadlock when we tried to queue | |
* that waiter. Drop the pi_state reference | |
* which we took above and remove the pointer | |
* to the state from the waiters futex_q | |
* object. | |
*/ | |
this->pi_state = NULL; | |
put_pi_state(pi_state); | |
/* | |
* We stop queueing more waiters and let user | |
* space deal with the mess. | |
*/ | |
break; | |
} | |
} | |
requeue_futex(this, hb1, hb2, &key2); | |
} | |
/* | |
* We took an extra initial reference to the pi_state either | |
* in futex_proxy_trylock_atomic() or in lookup_pi_state(). We | |
* need to drop it here again. | |
*/ | |
put_pi_state(pi_state); | |
out_unlock: | |
double_unlock_hb(hb1, hb2); | |
wake_up_q(&wake_q); | |
hb_waiters_dec(hb2); | |
return ret ? ret : task_count; | |
} | |
/* The key must be already stored in q->key. */ | |
static inline struct futex_hash_bucket *queue_lock(struct futex_q *q) | |
__acquires(&hb->lock) | |
{ | |
struct futex_hash_bucket *hb; | |
hb = hash_futex(&q->key); | |
/* | |
* Increment the counter before taking the lock so that | |
* a potential waker won't miss a to-be-slept task that is | |
* waiting for the spinlock. This is safe as all queue_lock() | |
* users end up calling queue_me(). Similarly, for housekeeping, | |
* decrement the counter at queue_unlock() when some error has | |
* occurred and we don't end up adding the task to the list. | |
*/ | |
hb_waiters_inc(hb); /* implies smp_mb(); (A) */ | |
q->lock_ptr = &hb->lock; | |
spin_lock(&hb->lock); | |
return hb; | |
} | |
static inline void | |
queue_unlock(struct futex_hash_bucket *hb) | |
__releases(&hb->lock) | |
{ | |
spin_unlock(&hb->lock); | |
hb_waiters_dec(hb); | |
} | |
static inline void __queue_me(struct futex_q *q, struct futex_hash_bucket *hb) | |
{ | |
int prio; | |
/* | |
* The priority used to register this element is | |
* - either the real thread-priority for the real-time threads | |
* (i.e. threads with a priority lower than MAX_RT_PRIO) | |
* - or MAX_RT_PRIO for non-RT threads. | |
* Thus, all RT-threads are woken first in priority order, and | |
* the others are woken last, in FIFO order. | |
*/ | |
prio = min(current->normal_prio, MAX_RT_PRIO); | |
plist_node_init(&q->list, prio); | |
plist_add(&q->list, &hb->chain); | |
q->task = current; | |
} | |
/** | |
* queue_me() - Enqueue the futex_q on the futex_hash_bucket | |
* @q: The futex_q to enqueue | |
* @hb: The destination hash bucket | |
* | |
* The hb->lock must be held by the caller, and is released here. A call to | |
* queue_me() is typically paired with exactly one call to unqueue_me(). The | |
* exceptions involve the PI related operations, which may use unqueue_me_pi() | |
* or nothing if the unqueue is done as part of the wake process and the unqueue | |
* state is implicit in the state of woken task (see futex_wait_requeue_pi() for | |
* an example). | |
*/ | |
static inline void queue_me(struct futex_q *q, struct futex_hash_bucket *hb) | |
__releases(&hb->lock) | |
{ | |
__queue_me(q, hb); | |
spin_unlock(&hb->lock); | |
} | |
/** | |
* unqueue_me() - Remove the futex_q from its futex_hash_bucket | |
* @q: The futex_q to unqueue | |
* | |
* The q->lock_ptr must not be held by the caller. A call to unqueue_me() must | |
* be paired with exactly one earlier call to queue_me(). | |
* | |
* Return: | |
* - 1 - if the futex_q was still queued (and we removed unqueued it); | |
* - 0 - if the futex_q was already removed by the waking thread | |
*/ | |
static int unqueue_me(struct futex_q *q) | |
{ | |
spinlock_t *lock_ptr; | |
int ret = 0; | |
/* In the common case we don't take the spinlock, which is nice. */ | |
retry: | |
/* | |
* q->lock_ptr can change between this read and the following spin_lock. | |
* Use READ_ONCE to forbid the compiler from reloading q->lock_ptr and | |
* optimizing lock_ptr out of the logic below. | |
*/ | |
lock_ptr = READ_ONCE(q->lock_ptr); | |
if (lock_ptr != NULL) { | |
spin_lock(lock_ptr); | |
/* | |
* q->lock_ptr can change between reading it and | |
* spin_lock(), causing us to take the wrong lock. This | |
* corrects the race condition. | |
* | |
* Reasoning goes like this: if we have the wrong lock, | |
* q->lock_ptr must have changed (maybe several times) | |
* between reading it and the spin_lock(). It can | |
* change again after the spin_lock() but only if it was | |
* already changed before the spin_lock(). It cannot, | |
* however, change back to the original value. Therefore | |
* we can detect whether we acquired the correct lock. | |
*/ | |
if (unlikely(lock_ptr != q->lock_ptr)) { | |
spin_unlock(lock_ptr); | |
goto retry; | |
} | |
__unqueue_futex(q); | |
BUG_ON(q->pi_state); | |
spin_unlock(lock_ptr); | |
ret = 1; | |
} | |
return ret; | |
} | |
/* | |
* PI futexes can not be requeued and must remove themself from the | |
* hash bucket. The hash bucket lock (i.e. lock_ptr) is held on entry | |
* and dropped here. | |
*/ | |
static void unqueue_me_pi(struct futex_q *q) | |
__releases(q->lock_ptr) | |
{ | |
__unqueue_futex(q); | |
BUG_ON(!q->pi_state); | |
put_pi_state(q->pi_state); | |
q->pi_state = NULL; | |
spin_unlock(q->lock_ptr); | |
} | |
static int fixup_pi_state_owner(u32 __user *uaddr, struct futex_q *q, | |
struct task_struct *argowner) | |
{ | |
struct futex_pi_state *pi_state = q->pi_state; | |
u32 uval, curval, newval; | |
struct task_struct *oldowner, *newowner; | |
u32 newtid; | |
int ret, err = 0; | |
lockdep_assert_held(q->lock_ptr); | |
raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock); | |
oldowner = pi_state->owner; | |
/* | |
* We are here because either: | |
* | |
* - we stole the lock and pi_state->owner needs updating to reflect | |
* that (@argowner == current), | |
* | |
* or: | |
* | |
* - someone stole our lock and we need to fix things to point to the | |
* new owner (@argowner == NULL). | |
* | |
* Either way, we have to replace the TID in the user space variable. | |
* This must be atomic as we have to preserve the owner died bit here. | |
* | |
* Note: We write the user space value _before_ changing the pi_state | |
* because we can fault here. Imagine swapped out pages or a fork | |
* that marked all the anonymous memory readonly for cow. | |
* | |
* Modifying pi_state _before_ the user space value would leave the | |
* pi_state in an inconsistent state when we fault here, because we | |
* need to drop the locks to handle the fault. This might be observed | |
* in the PID check in lookup_pi_state. | |
*/ | |
retry: | |
if (!argowner) { | |
if (oldowner != current) { | |
/* | |
* We raced against a concurrent self; things are | |
* already fixed up. Nothing to do. | |
*/ | |
ret = 0; | |
goto out_unlock; | |
} | |
if (__rt_mutex_futex_trylock(&pi_state->pi_mutex)) { | |
/* We got the lock after all, nothing to fix. */ | |
ret = 0; | |
goto out_unlock; | |
} | |
/* | |
* The trylock just failed, so either there is an owner or | |
* there is a higher priority waiter than this one. | |
*/ | |
newowner = rt_mutex_owner(&pi_state->pi_mutex); | |
/* | |
* If the higher priority waiter has not yet taken over the | |
* rtmutex then newowner is NULL. We can't return here with | |
* that state because it's inconsistent vs. the user space | |
* state. So drop the locks and try again. It's a valid | |
* situation and not any different from the other retry | |
* conditions. | |
*/ | |
if (unlikely(!newowner)) { | |
err = -EAGAIN; | |
goto handle_err; | |
} | |
} else { | |
WARN_ON_ONCE(argowner != current); | |
if (oldowner == current) { | |
/* | |
* We raced against a concurrent self; things are | |
* already fixed up. Nothing to do. | |
*/ | |
ret = 0; | |
goto out_unlock; | |
} | |
newowner = argowner; | |
} | |
newtid = task_pid_vnr(newowner) | FUTEX_WAITERS; | |
/* Owner died? */ | |
if (!pi_state->owner) | |
newtid |= FUTEX_OWNER_DIED; | |
err = get_futex_value_locked(&uval, uaddr); | |
if (err) | |
goto handle_err; | |
for (;;) { | |
newval = (uval & FUTEX_OWNER_DIED) | newtid; | |
err = cmpxchg_futex_value_locked(&curval, uaddr, uval, newval); | |
if (err) | |
goto handle_err; | |
if (curval == uval) | |
break; | |
uval = curval; | |
} | |
/* | |
* We fixed up user space. Now we need to fix the pi_state | |
* itself. | |
*/ | |
if (pi_state->owner != NULL) { | |
raw_spin_lock(&pi_state->owner->pi_lock); | |
WARN_ON(list_empty(&pi_state->list)); | |
list_del_init(&pi_state->list); | |
raw_spin_unlock(&pi_state->owner->pi_lock); | |
} | |
pi_state->owner = newowner; | |
raw_spin_lock(&newowner->pi_lock); | |
WARN_ON(!list_empty(&pi_state->list)); | |
list_add(&pi_state->list, &newowner->pi_state_list); | |
raw_spin_unlock(&newowner->pi_lock); | |
raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock); | |
return 0; | |
/* | |
* In order to reschedule or handle a page fault, we need to drop the | |
* locks here. In the case of a fault, this gives the other task | |
* (either the highest priority waiter itself or the task which stole | |
* the rtmutex) the chance to try the fixup of the pi_state. So once we | |
* are back from handling the fault we need to check the pi_state after | |
* reacquiring the locks and before trying to do another fixup. When | |
* the fixup has been done already we simply return. | |
* | |
* Note: we hold both hb->lock and pi_mutex->wait_lock. We can safely | |
* drop hb->lock since the caller owns the hb -> futex_q relation. | |
* Dropping the pi_mutex->wait_lock requires the state revalidate. | |
*/ | |
handle_err: | |
raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock); | |
spin_unlock(q->lock_ptr); | |
switch (err) { | |
case -EFAULT: | |
ret = fault_in_user_writeable(uaddr); | |
break; | |
case -EAGAIN: | |
cond_resched(); | |
ret = 0; | |
break; | |
default: | |
WARN_ON_ONCE(1); | |
ret = err; | |
break; | |
} | |
spin_lock(q->lock_ptr); | |
raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock); | |
/* | |
* Check if someone else fixed it for us: | |
*/ | |
if (pi_state->owner != oldowner) { | |
ret = 0; | |
goto out_unlock; | |
} | |
if (ret) | |
goto out_unlock; | |
goto retry; | |
out_unlock: | |
raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock); | |
return ret; | |
} | |
static long futex_wait_restart(struct restart_block *restart); | |
/** | |
* fixup_owner() - Post lock pi_state and corner case management | |
* @uaddr: user address of the futex | |
* @q: futex_q (contains pi_state and access to the rt_mutex) | |
* @locked: if the attempt to take the rt_mutex succeeded (1) or not (0) | |
* | |
* After attempting to lock an rt_mutex, this function is called to cleanup | |
* the pi_state owner as well as handle race conditions that may allow us to | |
* acquire the lock. Must be called with the hb lock held. | |
* | |
* Return: | |
* - 1 - success, lock taken; | |
* - 0 - success, lock not taken; | |
* - <0 - on error (-EFAULT) | |
*/ | |
static int fixup_owner(u32 __user *uaddr, struct futex_q *q, int locked) | |
{ | |
int ret = 0; | |
if (locked) { | |
/* | |
* Got the lock. We might not be the anticipated owner if we | |
* did a lock-steal - fix up the PI-state in that case: | |
* | |
* Speculative pi_state->owner read (we don't hold wait_lock); | |
* since we own the lock pi_state->owner == current is the | |
* stable state, anything else needs more attention. | |
*/ | |
if (q->pi_state->owner != current) | |
ret = fixup_pi_state_owner(uaddr, q, current); | |
return ret ? ret : locked; | |
} | |
/* | |
* If we didn't get the lock; check if anybody stole it from us. In | |
* that case, we need to fix up the uval to point to them instead of | |
* us, otherwise bad things happen. [10] | |
* | |
* Another speculative read; pi_state->owner == current is unstable | |
* but needs our attention. | |
*/ | |
if (q->pi_state->owner == current) { | |
ret = fixup_pi_state_owner(uaddr, q, NULL); | |
return ret; | |
} | |
/* | |
* Paranoia check. If we did not take the lock, then we should not be | |
* the owner of the rt_mutex. | |
*/ | |
if (rt_mutex_owner(&q->pi_state->pi_mutex) == current) { | |
printk(KERN_ERR "fixup_owner: ret = %d pi-mutex: %p " | |
"pi-state %p\n", ret, | |
q->pi_state->pi_mutex.owner, | |
q->pi_state->owner); | |
} | |
return ret; | |
} | |
/** | |
* futex_wait_queue_me() - queue_me() and wait for wakeup, timeout, or signal | |
* @hb: the futex hash bucket, must be locked by the caller | |
* @q: the futex_q to queue up on | |
* @timeout: the prepared hrtimer_sleeper, or null for no timeout | |
*/ | |
static void futex_wait_queue_me(struct futex_hash_bucket *hb, struct futex_q *q, | |
struct hrtimer_sleeper *timeout) | |
{ | |
/* | |
* The task state is guaranteed to be set before another task can | |
* wake it. set_current_state() is implemented using smp_store_mb() and | |
* queue_me() calls spin_unlock() upon completion, both serializing | |
* access to the hash list and forcing another memory barrier. | |
*/ | |
set_current_state(TASK_INTERRUPTIBLE); | |
queue_me(q, hb); | |
/* Arm the timer */ | |
if (timeout) | |
hrtimer_sleeper_start_expires(timeout, HRTIMER_MODE_ABS); | |
/* | |
* If we have been removed from the hash list, then another task | |
* has tried to wake us, and we can skip the call to schedule(). | |
*/ | |
if (likely(!plist_node_empty(&q->list))) { | |
/* | |
* If the timer has already expired, current will already be | |
* flagged for rescheduling. Only call schedule if there | |
* is no timeout, or if it has yet to expire. | |
*/ | |
if (!timeout || timeout->task) | |
freezable_schedule(); | |
} | |
__set_current_state(TASK_RUNNING); | |
} | |
/** | |
* futex_wait_setup() - Prepare to wait on a futex | |
* @uaddr: the futex userspace address | |
* @val: the expected value | |
* @flags: futex flags (FLAGS_SHARED, etc.) | |
* @q: the associated futex_q | |
* @hb: storage for hash_bucket pointer to be returned to caller | |
* | |
* Setup the futex_q and locate the hash_bucket. Get the futex value and | |
* compare it with the expected value. Handle atomic faults internally. | |
* Return with the hb lock held and a q.key reference on success, and unlocked | |
* with no q.key reference on failure. | |
* | |
* Return: | |
* - 0 - uaddr contains val and hb has been locked; | |
* - <1 - -EFAULT or -EWOULDBLOCK (uaddr does not contain val) and hb is unlocked | |
*/ | |
static int futex_wait_setup(u32 __user *uaddr, u32 val, unsigned int flags, | |
struct futex_q *q, struct futex_hash_bucket **hb) | |
{ | |
u32 uval; | |
int ret; | |
/* | |
* Access the page AFTER the hash-bucket is locked. | |
* Order is important: | |
* | |
* Userspace waiter: val = var; if (cond(val)) futex_wait(&var, val); | |
* Userspace waker: if (cond(var)) { var = new; futex_wake(&var); } | |
* | |
* The basic logical guarantee of a futex is that it blocks ONLY | |
* if cond(var) is known to be true at the time of blocking, for | |
* any cond. If we locked the hash-bucket after testing *uaddr, that | |
* would open a race condition where we could block indefinitely with | |
* cond(var) false, which would violate the guarantee. | |
* | |
* On the other hand, we insert q and release the hash-bucket only | |
* after testing *uaddr. This guarantees that futex_wait() will NOT | |
* absorb a wakeup if *uaddr does not match the desired values | |
* while the syscall executes. | |
*/ | |
retry: | |
ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &q->key, FUTEX_READ); | |
if (unlikely(ret != 0)) | |
return ret; | |
retry_private: | |
*hb = queue_lock(q); | |
ret = get_futex_value_locked(&uval, uaddr); | |
if (ret) { | |
queue_unlock(*hb); | |
ret = get_user(uval, uaddr); | |
if (ret) | |
return ret; | |
if (!(flags & FLAGS_SHARED)) | |
goto retry_private; | |
goto retry; | |
} | |
if (uval != val) { | |
queue_unlock(*hb); | |
ret = -EWOULDBLOCK; | |
} | |
return ret; | |
} | |
static int futex_wait(u32 __user *uaddr, unsigned int flags, u32 val, | |
ktime_t *abs_time, u32 bitset) | |
{ | |
struct hrtimer_sleeper timeout, *to; | |
struct restart_block *restart; | |
struct futex_hash_bucket *hb; | |
struct futex_q q = futex_q_init; | |
int ret; | |
if (!bitset) | |
return -EINVAL; | |
q.bitset = bitset; | |
to = futex_setup_timer(abs_time, &timeout, flags, | |
current->timer_slack_ns); | |
retry: | |
/* | |
* Prepare to wait on uaddr. On success, holds hb lock and increments | |
* q.key refs. | |
*/ | |
ret = futex_wait_setup(uaddr, val, flags, &q, &hb); | |
if (ret) | |
goto out; | |
/* queue_me and wait for wakeup, timeout, or a signal. */ | |
futex_wait_queue_me(hb, &q, to); | |
/* If we were woken (and unqueued), we succeeded, whatever. */ | |
ret = 0; | |
/* unqueue_me() drops q.key ref */ | |
if (!unqueue_me(&q)) | |
goto out; | |
ret = -ETIMEDOUT; | |
if (to && !to->task) | |
goto out; | |
/* | |
* We expect signal_pending(current), but we might be the | |
* victim of a spurious wakeup as well. | |
*/ | |
if (!signal_pending(current)) | |
goto retry; | |
ret = -ERESTARTSYS; | |
if (!abs_time) | |
goto out; | |
restart = ¤t->restart_block; | |
restart->fn = futex_wait_restart; | |
restart->futex.uaddr = uaddr; | |
restart->futex.val = val; | |
restart->futex.time = *abs_time; | |
restart->futex.bitset = bitset; | |
restart->futex.flags = flags | FLAGS_HAS_TIMEOUT; | |
ret = -ERESTART_RESTARTBLOCK; | |
out: | |
if (to) { | |
hrtimer_cancel(&to->timer); | |
destroy_hrtimer_on_stack(&to->timer); | |
} | |
return ret; | |
} | |
static long futex_wait_restart(struct restart_block *restart) | |
{ | |
u32 __user *uaddr = restart->futex.uaddr; | |
ktime_t t, *tp = NULL; | |
if (restart->futex.flags & FLAGS_HAS_TIMEOUT) { | |
t = restart->futex.time; | |
tp = &t; | |
} | |
restart->fn = do_no_restart_syscall; | |
return (long)futex_wait(uaddr, restart->futex.flags, | |
restart->futex.val, tp, restart->futex.bitset); | |
} | |
/* | |
* Userspace tried a 0 -> TID atomic transition of the futex value | |
* and failed. The kernel side here does the whole locking operation: | |
* if there are waiters then it will block as a consequence of relying | |
* on rt-mutexes, it does PI, etc. (Due to races the kernel might see | |
* a 0 value of the futex too.). | |
* | |
* Also serves as futex trylock_pi()'ing, and due semantics. | |
*/ | |
static int futex_lock_pi(u32 __user *uaddr, unsigned int flags, | |
ktime_t *time, int trylock) | |
{ | |
struct hrtimer_sleeper timeout, *to; | |
struct futex_pi_state *pi_state = NULL; | |
struct task_struct *exiting = NULL; | |
struct rt_mutex_waiter rt_waiter; | |
struct futex_hash_bucket *hb; | |
struct futex_q q = futex_q_init; | |
int res, ret; | |
if (!IS_ENABLED(CONFIG_FUTEX_PI)) | |
return -ENOSYS; | |
if (refill_pi_state_cache()) | |
return -ENOMEM; | |
to = futex_setup_timer(time, &timeout, FLAGS_CLOCKRT, 0); | |
retry: | |
ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &q.key, FUTEX_WRITE); | |
if (unlikely(ret != 0)) | |
goto out; | |
retry_private: | |
hb = queue_lock(&q); | |
ret = futex_lock_pi_atomic(uaddr, hb, &q.key, &q.pi_state, current, | |
&exiting, 0); | |
if (unlikely(ret)) { | |
/* | |
* Atomic work succeeded and we got the lock, | |
* or failed. Either way, we do _not_ block. | |
*/ | |
switch (ret) { | |
case 1: | |
/* We got the lock. */ | |
ret = 0; | |
goto out_unlock_put_key; | |
case -EFAULT: | |
goto uaddr_faulted; | |
case -EBUSY: | |
case -EAGAIN: | |
/* | |
* Two reasons for this: | |
* - EBUSY: Task is exiting and we just wait for the | |
* exit to complete. | |
* - EAGAIN: The user space value changed. | |
*/ | |
queue_unlock(hb); | |
/* | |
* Handle the case where the owner is in the middle of | |
* exiting. Wait for the exit to complete otherwise | |
* this task might loop forever, aka. live lock. | |
*/ | |
wait_for_owner_exiting(ret, exiting); | |
cond_resched(); | |
goto retry; | |
default: | |
goto out_unlock_put_key; | |
} | |
} | |
WARN_ON(!q.pi_state); | |
/* | |
* Only actually queue now that the atomic ops are done: | |
*/ | |
__queue_me(&q, hb); | |
if (trylock) { | |
ret = rt_mutex_futex_trylock(&q.pi_state->pi_mutex); | |
/* Fixup the trylock return value: */ | |
ret = ret ? 0 : -EWOULDBLOCK; | |
goto no_block; | |
} | |
rt_mutex_init_waiter(&rt_waiter); | |
/* | |
* On PREEMPT_RT_FULL, when hb->lock becomes an rt_mutex, we must not | |
* hold it while doing rt_mutex_start_proxy(), because then it will | |
* include hb->lock in the blocking chain, even through we'll not in | |
* fact hold it while blocking. This will lead it to report -EDEADLK | |
* and BUG when futex_unlock_pi() interleaves with this. | |
* | |
* Therefore acquire wait_lock while holding hb->lock, but drop the | |
* latter before calling __rt_mutex_start_proxy_lock(). This | |
* interleaves with futex_unlock_pi() -- which does a similar lock | |
* handoff -- such that the latter can observe the futex_q::pi_state | |
* before __rt_mutex_start_proxy_lock() is done. | |
*/ | |
raw_spin_lock_irq(&q.pi_state->pi_mutex.wait_lock); | |
spin_unlock(q.lock_ptr); | |
/* | |
* __rt_mutex_start_proxy_lock() unconditionally enqueues the @rt_waiter | |
* such that futex_unlock_pi() is guaranteed to observe the waiter when | |
* it sees the futex_q::pi_state. | |
*/ | |
ret = __rt_mutex_start_proxy_lock(&q.pi_state->pi_mutex, &rt_waiter, current); | |
raw_spin_unlock_irq(&q.pi_state->pi_mutex.wait_lock); | |
if (ret) { | |
if (ret == 1) | |
ret = 0; | |
goto cleanup; | |
} | |
if (unlikely(to)) | |
hrtimer_sleeper_start_expires(to, HRTIMER_MODE_ABS); | |
ret = rt_mutex_wait_proxy_lock(&q.pi_state->pi_mutex, to, &rt_waiter); | |
cleanup: | |
spin_lock(q.lock_ptr); | |
/* | |
* If we failed to acquire the lock (deadlock/signal/timeout), we must | |
* first acquire the hb->lock before removing the lock from the | |
* rt_mutex waitqueue, such that we can keep the hb and rt_mutex wait | |
* lists consistent. | |
* | |
* In particular; it is important that futex_unlock_pi() can not | |
* observe this inconsistency. | |
*/ | |
if (ret && !rt_mutex_cleanup_proxy_lock(&q.pi_state->pi_mutex, &rt_waiter)) | |
ret = 0; | |
no_block: | |
/* | |
* Fixup the pi_state owner and possibly acquire the lock if we | |
* haven't already. | |
*/ | |
res = fixup_owner(uaddr, &q, !ret); | |
/* | |
* If fixup_owner() returned an error, proprogate that. If it acquired | |
* the lock, clear our -ETIMEDOUT or -EINTR. | |
*/ | |
if (res) | |
ret = (res < 0) ? res : 0; | |
/* | |
* If fixup_owner() faulted and was unable to handle the fault, unlock | |
* it and return the fault to userspace. | |
*/ | |
if (ret && (rt_mutex_owner(&q.pi_state->pi_mutex) == current)) { | |
pi_state = q.pi_state; | |
get_pi_state(pi_state); | |
} | |
/* Unqueue and drop the lock */ | |
unqueue_me_pi(&q); | |
if (pi_state) { | |
rt_mutex_futex_unlock(&pi_state->pi_mutex); | |
put_pi_state(pi_state); | |
} | |
goto out; | |
out_unlock_put_key: | |
queue_unlock(hb); | |
out: | |
if (to) { | |
hrtimer_cancel(&to->timer); | |
destroy_hrtimer_on_stack(&to->timer); | |
} | |
return ret != -EINTR ? ret : -ERESTARTNOINTR; | |
uaddr_faulted: | |
queue_unlock(hb); | |
ret = fault_in_user_writeable(uaddr); | |
if (ret) | |
goto out; | |
if (!(flags & FLAGS_SHARED)) | |
goto retry_private; | |
goto retry; | |
} | |
/* | |
* Userspace attempted a TID -> 0 atomic transition, and failed. | |
* This is the in-kernel slowpath: we look up the PI state (if any), | |
* and do the rt-mutex unlock. | |
*/ | |
static int futex_unlock_pi(u32 __user *uaddr, unsigned int flags) | |
{ | |
u32 curval, uval, vpid = task_pid_vnr(current); | |
union futex_key key = FUTEX_KEY_INIT; | |
struct futex_hash_bucket *hb; | |
struct futex_q *top_waiter; | |
int ret; | |
if (!IS_ENABLED(CONFIG_FUTEX_PI)) | |
return -ENOSYS; | |
retry: | |
if (get_user(uval, uaddr)) | |
return -EFAULT; | |
/* | |
* We release only a lock we actually own: | |
*/ | |
if ((uval & FUTEX_TID_MASK) != vpid) | |
return -EPERM; | |
ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &key, FUTEX_WRITE); | |
if (ret) | |
return ret; | |
hb = hash_futex(&key); | |
spin_lock(&hb->lock); | |
/* | |
* Check waiters first. We do not trust user space values at | |
* all and we at least want to know if user space fiddled | |
* with the futex value instead of blindly unlocking. | |
*/ | |
top_waiter = futex_top_waiter(hb, &key); | |
if (top_waiter) { | |
struct futex_pi_state *pi_state = top_waiter->pi_state; | |
ret = -EINVAL; | |
if (!pi_state) | |
goto out_unlock; | |
/* | |
* If current does not own the pi_state then the futex is | |
* inconsistent and user space fiddled with the futex value. | |
*/ | |
if (pi_state->owner != current) | |
goto out_unlock; | |
get_pi_state(pi_state); | |
/* | |
* By taking wait_lock while still holding hb->lock, we ensure | |
* there is no point where we hold neither; and therefore | |
* wake_futex_pi() must observe a state consistent with what we | |
* observed. | |
* | |
* In particular; this forces __rt_mutex_start_proxy() to | |
* complete such that we're guaranteed to observe the | |
* rt_waiter. Also see the WARN in wake_futex_pi(). | |
*/ | |
raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock); | |
spin_unlock(&hb->lock); | |
/* drops pi_state->pi_mutex.wait_lock */ | |
ret = wake_futex_pi(uaddr, uval, pi_state); | |
put_pi_state(pi_state); | |
/* | |
* Success, we're done! No tricky corner cases. | |
*/ | |
if (!ret) | |
goto out_putkey; | |
/* | |
* The atomic access to the futex value generated a | |
* pagefault, so retry the user-access and the wakeup: | |
*/ | |
if (ret == -EFAULT) | |
goto pi_faulted; | |
/* | |
* A unconditional UNLOCK_PI op raced against a waiter | |
* setting the FUTEX_WAITERS bit. Try again. | |
*/ | |
if (ret == -EAGAIN) | |
goto pi_retry; | |
/* | |
* wake_futex_pi has detected invalid state. Tell user | |
* space. | |
*/ | |
goto out_putkey; | |
} | |
/* | |
* We have no kernel internal state, i.e. no waiters in the | |
* kernel. Waiters which are about to queue themselves are stuck | |
* on hb->lock. So we can safely ignore them. We do neither | |
* preserve the WAITERS bit not the OWNER_DIED one. We are the | |
* owner. | |
*/ | |
if ((ret = cmpxchg_futex_value_locked(&curval, uaddr, uval, 0))) { | |
spin_unlock(&hb->lock); | |
switch (ret) { | |
case -EFAULT: | |
goto pi_faulted; | |
case -EAGAIN: | |
goto pi_retry; | |
default: | |
WARN_ON_ONCE(1); | |
goto out_putkey; | |
} | |
} | |
/* | |
* If uval has changed, let user space handle it. | |
*/ | |
ret = (curval == uval) ? 0 : -EAGAIN; | |
out_unlock: | |
spin_unlock(&hb->lock); | |
out_putkey: | |
return ret; | |
pi_retry: | |
cond_resched(); | |
goto retry; | |
pi_faulted: | |
ret = fault_in_user_writeable(uaddr); | |
if (!ret) | |
goto retry; | |
return ret; | |
} | |
/** | |
* handle_early_requeue_pi_wakeup() - Detect early wakeup on the initial futex | |
* @hb: the hash_bucket futex_q was original enqueued on | |
* @q: the futex_q woken while waiting to be requeued | |
* @key2: the futex_key of the requeue target futex | |
* @timeout: the timeout associated with the wait (NULL if none) | |
* | |
* Detect if the task was woken on the initial futex as opposed to the requeue | |
* target futex. If so, determine if it was a timeout or a signal that caused | |
* the wakeup and return the appropriate error code to the caller. Must be | |
* called with the hb lock held. | |
* | |
* Return: | |
* - 0 = no early wakeup detected; | |
* - <0 = -ETIMEDOUT or -ERESTARTNOINTR | |
*/ | |
static inline | |
int handle_early_requeue_pi_wakeup(struct futex_hash_bucket *hb, | |
struct futex_q *q, union futex_key *key2, | |
struct hrtimer_sleeper *timeout) | |
{ | |
int ret = 0; | |
/* | |
* With the hb lock held, we avoid races while we process the wakeup. | |
* We only need to hold hb (and not hb2) to ensure atomicity as the | |
* wakeup code can't change q.key from uaddr to uaddr2 if we hold hb. | |
* It can't be requeued from uaddr2 to something else since we don't | |
* support a PI aware source futex for requeue. | |
*/ | |
if (!match_futex(&q->key, key2)) { | |
WARN_ON(q->lock_ptr && (&hb->lock != q->lock_ptr)); | |
/* | |
* We were woken prior to requeue by a timeout or a signal. | |
* Unqueue the futex_q and determine which it was. | |
*/ | |
plist_del(&q->list, &hb->chain); | |
hb_waiters_dec(hb); | |
/* Handle spurious wakeups gracefully */ | |
ret = -EWOULDBLOCK; | |
if (timeout && !timeout->task) | |
ret = -ETIMEDOUT; | |
else if (signal_pending(current)) | |
ret = -ERESTARTNOINTR; | |
} | |
return ret; | |
} | |
/** | |
* futex_wait_requeue_pi() - Wait on uaddr and take uaddr2 | |
* @uaddr: the futex we initially wait on (non-pi) | |
* @flags: futex flags (FLAGS_SHARED, FLAGS_CLOCKRT, etc.), they must be | |
* the same type, no requeueing from private to shared, etc. | |
* @val: the expected value of uaddr | |
* @abs_time: absolute timeout | |
* @bitset: 32 bit wakeup bitset set by userspace, defaults to all | |
* @uaddr2: the pi futex we will take prior to returning to user-space | |
* | |
* The caller will wait on uaddr and will be requeued by futex_requeue() to | |
* uaddr2 which must be PI aware and unique from uaddr. Normal wakeup will wake | |
* on uaddr2 and complete the acquisition of the rt_mutex prior to returning to | |
* userspace. This ensures the rt_mutex maintains an owner when it has waiters; | |
* without one, the pi logic would not know which task to boost/deboost, if | |
* there was a need to. | |
* | |
* We call schedule in futex_wait_queue_me() when we enqueue and return there | |
* via the following-- | |
* 1) wakeup on uaddr2 after an atomic lock acquisition by futex_requeue() | |
* 2) wakeup on uaddr2 after a requeue | |
* 3) signal | |
* 4) timeout | |
* | |
* If 3, cleanup and return -ERESTARTNOINTR. | |
* | |
* If 2, we may then block on trying to take the rt_mutex and return via: | |
* 5) successful lock | |
* 6) signal | |
* 7) timeout | |
* 8) other lock acquisition failure | |
* | |
* If 6, return -EWOULDBLOCK (restarting the syscall would do the same). | |
* | |
* If 4 or 7, we cleanup and return with -ETIMEDOUT. | |
* | |
* Return: | |
* - 0 - On success; | |
* - <0 - On error | |
*/ | |
static int futex_wait_requeue_pi(u32 __user *uaddr, unsigned int flags, | |
u32 val, ktime_t *abs_time, u32 bitset, | |
u32 __user *uaddr2) | |
{ | |
struct hrtimer_sleeper timeout, *to; | |
struct futex_pi_state *pi_state = NULL; | |
struct rt_mutex_waiter rt_waiter; | |
struct futex_hash_bucket *hb; | |
union futex_key key2 = FUTEX_KEY_INIT; | |
struct futex_q q = futex_q_init; | |
int res, ret; | |
if (!IS_ENABLED(CONFIG_FUTEX_PI)) | |
return -ENOSYS; | |
if (uaddr == uaddr2) | |
return -EINVAL; | |
if (!bitset) | |
return -EINVAL; | |
to = futex_setup_timer(abs_time, &timeout, flags, | |
current->timer_slack_ns); | |
/* | |
* The waiter is allocated on our stack, manipulated by the requeue | |
* code while we sleep on uaddr. | |
*/ | |
rt_mutex_init_waiter(&rt_waiter); | |
ret = get_futex_key(uaddr2, flags & FLAGS_SHARED, &key2, FUTEX_WRITE); | |
if (unlikely(ret != 0)) | |
goto out; | |
q.bitset = bitset; | |
q.rt_waiter = &rt_waiter; | |
q.requeue_pi_key = &key2; | |
/* | |
* Prepare to wait on uaddr. On success, increments q.key (key1) ref | |
* count. | |
*/ | |
ret = futex_wait_setup(uaddr, val, flags, &q, &hb); | |
if (ret) | |
goto out; | |
/* | |
* The check above which compares uaddrs is not sufficient for | |
* shared futexes. We need to compare the keys: | |
*/ | |
if (match_futex(&q.key, &key2)) { | |
queue_unlock(hb); | |
ret = -EINVAL; | |
goto out; | |
} | |
/* Queue the futex_q, drop the hb lock, wait for wakeup. */ | |
futex_wait_queue_me(hb, &q, to); | |
spin_lock(&hb->lock); | |
ret = handle_early_requeue_pi_wakeup(hb, &q, &key2, to); | |
spin_unlock(&hb->lock); | |
if (ret) | |
goto out; | |
/* | |
* In order for us to be here, we know our q.key == key2, and since | |
* we took the hb->lock above, we also know that futex_requeue() has | |
* completed and we no longer have to concern ourselves with a wakeup | |
* race with the atomic proxy lock acquisition by the requeue code. The | |
* futex_requeue dropped our key1 reference and incremented our key2 | |
* reference count. | |
*/ | |
/* Check if the requeue code acquired the second futex for us. */ | |
if (!q.rt_waiter) { | |
/* | |
* Got the lock. We might not be the anticipated owner if we | |
* did a lock-steal - fix up the PI-state in that case. | |
*/ | |
if (q.pi_state && (q.pi_state->owner != current)) { | |
spin_lock(q.lock_ptr); | |
ret = fixup_pi_state_owner(uaddr2, &q, current); | |
if (ret && rt_mutex_owner(&q.pi_state->pi_mutex) == current) { | |
pi_state = q.pi_state; | |
get_pi_state(pi_state); | |
} | |
/* | |
* Drop the reference to the pi state which | |
* the requeue_pi() code acquired for us. | |
*/ | |
put_pi_state(q.pi_state); | |
spin_unlock(q.lock_ptr); | |
} | |
} else { | |
struct rt_mutex *pi_mutex; | |
/* | |
* We have been woken up by futex_unlock_pi(), a timeout, or a | |
* signal. futex_unlock_pi() will not destroy the lock_ptr nor | |
* the pi_state. | |
*/ | |
WARN_ON(!q.pi_state); | |
pi_mutex = &q.pi_state->pi_mutex; | |
ret = rt_mutex_wait_proxy_lock(pi_mutex, to, &rt_waiter); | |
spin_lock(q.lock_ptr); | |
if (ret && !rt_mutex_cleanup_proxy_lock(pi_mutex, &rt_waiter)) | |
ret = 0; | |
debug_rt_mutex_free_waiter(&rt_waiter); | |
/* | |
* Fixup the pi_state owner and possibly acquire the lock if we | |
* haven't already. | |
*/ | |
res = fixup_owner(uaddr2, &q, !ret); | |
/* | |
* If fixup_owner() returned an error, proprogate that. If it | |
* acquired the lock, clear -ETIMEDOUT or -EINTR. | |
*/ | |
if (res) | |
ret = (res < 0) ? res : 0; | |
/* | |
* If fixup_pi_state_owner() faulted and was unable to handle | |
* the fault, unlock the rt_mutex and return the fault to | |
* userspace. | |
*/ | |
if (ret && rt_mutex_owner(&q.pi_state->pi_mutex) == current) { | |
pi_state = q.pi_state; | |
get_pi_state(pi_state); | |
} | |
/* Unqueue and drop the lock. */ | |
unqueue_me_pi(&q); | |
} | |
if (pi_state) { | |
rt_mutex_futex_unlock(&pi_state->pi_mutex); | |
put_pi_state(pi_state); | |
} | |
if (ret == -EINTR) { | |
/* | |
* We've already been requeued, but cannot restart by calling | |
* futex_lock_pi() directly. We could restart this syscall, but | |
* it would detect that the user space "val" changed and return | |
* -EWOULDBLOCK. Save the overhead of the restart and return | |
* -EWOULDBLOCK directly. | |
*/ | |
ret = -EWOULDBLOCK; | |
} | |
out: | |
if (to) { | |
hrtimer_cancel(&to->timer); | |
destroy_hrtimer_on_stack(&to->timer); | |
} | |
return ret; | |
} | |
/* | |
* Support for robust futexes: the kernel cleans up held futexes at | |
* thread exit time. | |
* | |
* Implementation: user-space maintains a per-thread list of locks it | |
* is holding. Upon do_exit(), the kernel carefully walks this list, | |
* and marks all locks that are owned by this thread with the | |
* FUTEX_OWNER_DIED bit, and wakes up a waiter (if any). The list is | |
* always manipulated with the lock held, so the list is private and | |
* per-thread. Userspace also maintains a per-thread 'list_op_pending' | |
* field, to allow the kernel to clean up if the thread dies after | |
* acquiring the lock, but just before it could have added itself to | |
* the list. There can only be one such pending lock. | |
*/ | |
/** | |
* sys_set_robust_list() - Set the robust-futex list head of a task | |
* @head: pointer to the list-head | |
* @len: length of the list-head, as userspace expects | |
*/ | |
SYSCALL_DEFINE2(set_robust_list, struct robust_list_head __user *, head, | |
size_t, len) | |
{ | |
if (!futex_cmpxchg_enabled) | |
return -ENOSYS; | |
/* | |
* The kernel knows only one size for now: | |
*/ | |
if (unlikely(len != sizeof(*head))) | |
return -EINVAL; | |
current->robust_list = head; | |
return 0; | |
} | |
/** | |
* sys_get_robust_list() - Get the robust-futex list head of a task | |
* @pid: pid of the process [zero for current task] | |
* @head_ptr: pointer to a list-head pointer, the kernel fills it in | |
* @len_ptr: pointer to a length field, the kernel fills in the header size | |
*/ | |
SYSCALL_DEFINE3(get_robust_list, int, pid, | |
struct robust_list_head __user * __user *, head_ptr, | |
size_t __user *, len_ptr) | |
{ | |
struct robust_list_head __user *head; | |
unsigned long ret; | |
struct task_struct *p; | |
if (!futex_cmpxchg_enabled) | |
return -ENOSYS; | |
rcu_read_lock(); | |
ret = -ESRCH; | |
if (!pid) | |
p = current; | |
else { | |
p = find_task_by_vpid(pid); | |
if (!p) | |
goto err_unlock; | |
} | |
ret = -EPERM; | |
if (!ptrace_may_access(p, PTRACE_MODE_READ_REALCREDS)) | |
goto err_unlock; | |
head = p->robust_list; | |
rcu_read_unlock(); | |
if (put_user(sizeof(*head), len_ptr)) | |
return -EFAULT; | |
return put_user(head, head_ptr); | |
err_unlock: | |
rcu_read_unlock(); | |
return ret; | |
} | |
/* Constants for the pending_op argument of handle_futex_death */ | |
#define HANDLE_DEATH_PENDING true | |
#define HANDLE_DEATH_LIST false | |
/* | |
* Process a futex-list entry, check whether it's owned by the | |
* dying task, and do notification if so: | |
*/ | |
static int handle_futex_death(u32 __user *uaddr, struct task_struct *curr, | |
bool pi, bool pending_op) | |
{ | |
u32 uval, nval, mval; | |
int err; | |
/* Futex address must be 32bit aligned */ | |
if ((((unsigned long)uaddr) % sizeof(*uaddr)) != 0) | |
return -1; | |
retry: | |
if (get_user(uval, uaddr)) | |
return -1; | |
/* | |
* Special case for regular (non PI) futexes. The unlock path in | |
* user space has two race scenarios: | |
* | |
* 1. The unlock path releases the user space futex value and | |
* before it can execute the futex() syscall to wake up | |
* waiters it is killed. | |
* | |
* 2. A woken up waiter is killed before it can acquire the | |
* futex in user space. | |
* | |
* In both cases the TID validation below prevents a wakeup of | |
* potential waiters which can cause these waiters to block | |
* forever. | |
* | |
* In both cases the following conditions are met: | |
* | |
* 1) task->robust_list->list_op_pending != NULL | |
* @pending_op == true | |
* 2) User space futex value == 0 | |
* 3) Regular futex: @pi == false | |
* | |
* If these conditions are met, it is safe to attempt waking up a | |
* potential waiter without touching the user space futex value and | |
* trying to set the OWNER_DIED bit. The user space futex value is | |
* uncontended and the rest of the user space mutex state is | |
* consistent, so a woken waiter will just take over the | |
* uncontended futex. Setting the OWNER_DIED bit would create | |
* inconsistent state and malfunction of the user space owner died | |
* handling. | |
*/ | |
if (pending_op && !pi && !uval) { | |
futex_wake(uaddr, 1, 1, FUTEX_BITSET_MATCH_ANY); | |
return 0; | |
} | |
if ((uval & FUTEX_TID_MASK) != task_pid_vnr(curr)) | |
return 0; | |
/* | |
* Ok, this dying thread is truly holding a futex | |
* of interest. Set the OWNER_DIED bit atomically | |
* via cmpxchg, and if the value had FUTEX_WAITERS | |
* set, wake up a waiter (if any). (We have to do a | |
* futex_wake() even if OWNER_DIED is already set - | |
* to handle the rare but possible case of recursive | |
* thread-death.) The rest of the cleanup is done in | |
* userspace. | |
*/ | |
mval = (uval & FUTEX_WAITERS) | FUTEX_OWNER_DIED; | |
/* | |
* We are not holding a lock here, but we want to have | |
* the pagefault_disable/enable() protection because | |
* we want to handle the fault gracefully. If the | |
* access fails we try to fault in the futex with R/W | |
* verification via get_user_pages. get_user() above | |
* does not guarantee R/W access. If that fails we | |
* give up and leave the futex locked. | |
*/ | |
if ((err = cmpxchg_futex_value_locked(&nval, uaddr, uval, mval))) { | |
switch (err) { | |
case -EFAULT: | |
if (fault_in_user_writeable(uaddr)) | |
return -1; | |
goto retry; | |
case -EAGAIN: | |
cond_resched(); | |
goto retry; | |
default: | |
WARN_ON_ONCE(1); | |
return err; | |
} | |
} | |
if (nval != uval) | |
goto retry; | |
/* | |
* Wake robust non-PI futexes here. The wakeup of | |
* PI futexes happens in exit_pi_state(): | |
*/ | |
if (!pi && (uval & FUTEX_WAITERS)) | |
futex_wake(uaddr, 1, 1, FUTEX_BITSET_MATCH_ANY); | |
return 0; | |
} | |
/* | |
* Fetch a robust-list pointer. Bit 0 signals PI futexes: | |
*/ | |
static inline int fetch_robust_entry(struct robust_list __user **entry, | |
struct robust_list __user * __user *head, | |
unsigned int *pi) | |
{ | |
unsigned long uentry; | |
if (get_user(uentry, (unsigned long __user *)head)) | |
return -EFAULT; | |
*entry = (void __user *)(uentry & ~1UL); | |
*pi = uentry & 1; | |
return 0; | |
} | |
/* | |
* Walk curr->robust_list (very carefully, it's a userspace list!) | |
* and mark any locks found there dead, and notify any waiters. | |
* | |
* We silently return on any sign of list-walking problem. | |
*/ | |
static void exit_robust_list(struct task_struct *curr) | |
{ | |
struct robust_list_head __user *head = curr->robust_list; | |
struct robust_list __user *entry, *next_entry, *pending; | |
unsigned int limit = ROBUST_LIST_LIMIT, pi, pip; | |
unsigned int next_pi; | |
unsigned long futex_offset; | |
int rc; | |
if (!futex_cmpxchg_enabled) | |
return; | |
/* | |
* Fetch the list head (which was registered earlier, via | |
* sys_set_robust_list()): | |
*/ | |
if (fetch_robust_entry(&entry, &head->list.next, &pi)) | |
return; | |
/* | |
* Fetch the relative futex offset: | |
*/ | |
if (get_user(futex_offset, &head->futex_offset)) | |
return; | |
/* | |
* Fetch any possibly pending lock-add first, and handle it | |
* if it exists: | |
*/ | |
if (fetch_robust_entry(&pending, &head->list_op_pending, &pip)) | |
return; | |
next_entry = NULL; /* avoid warning with gcc */ | |
while (entry != &head->list) { | |
/* | |
* Fetch the next entry in the list before calling | |
* handle_futex_death: | |
*/ | |
rc = fetch_robust_entry(&next_entry, &entry->next, &next_pi); | |
/* | |
* A pending lock might already be on the list, so | |
* don't process it twice: | |
*/ | |
if (entry != pending) { | |
if (handle_futex_death((void __user *)entry + futex_offset, | |
curr, pi, HANDLE_DEATH_LIST)) | |
return; | |
} | |
if (rc) | |
return; | |
entry = next_entry; | |
pi = next_pi; | |
/* | |
* Avoid excessively long or circular lists: | |
*/ | |
if (!--limit) | |
break; | |
cond_resched(); | |
} | |
if (pending) { | |
handle_futex_death((void __user *)pending + futex_offset, | |
curr, pip, HANDLE_DEATH_PENDING); | |
} | |
} | |
static void futex_cleanup(struct task_struct *tsk) | |
{ | |
if (unlikely(tsk->robust_list)) { | |
exit_robust_list(tsk); | |
tsk->robust_list = NULL; | |
} | |
#ifdef CONFIG_COMPAT | |
if (unlikely(tsk->compat_robust_list)) { | |
compat_exit_robust_list(tsk); | |
tsk->compat_robust_list = NULL; | |
} | |
#endif | |
if (unlikely(!list_empty(&tsk->pi_state_list))) | |
exit_pi_state_list(tsk); | |
} | |
/** | |
* futex_exit_recursive - Set the tasks futex state to FUTEX_STATE_DEAD | |
* @tsk: task to set the state on | |
* | |
* Set the futex exit state of the task lockless. The futex waiter code | |
* observes that state when a task is exiting and loops until the task has | |
* actually finished the futex cleanup. The worst case for this is that the | |
* waiter runs through the wait loop until the state becomes visible. | |
* | |
* This is called from the recursive fault handling path in do_exit(). | |
* | |
* This is best effort. Either the futex exit code has run already or | |
* not. If the OWNER_DIED bit has been set on the futex then the waiter can | |
* take it over. If not, the problem is pushed back to user space. If the | |
* futex exit code did not run yet, then an already queued waiter might | |
* block forever, but there is nothing which can be done about that. | |
*/ | |
void futex_exit_recursive(struct task_struct *tsk) | |
{ | |
/* If the state is FUTEX_STATE_EXITING then futex_exit_mutex is held */ | |
if (tsk->futex_state == FUTEX_STATE_EXITING) | |
mutex_unlock(&tsk->futex_exit_mutex); | |
tsk->futex_state = FUTEX_STATE_DEAD; | |
} | |
static void futex_cleanup_begin(struct task_struct *tsk) | |
{ | |
/* | |
* Prevent various race issues against a concurrent incoming waiter | |
* including live locks by forcing the waiter to block on | |
* tsk->futex_exit_mutex when it observes FUTEX_STATE_EXITING in | |
* attach_to_pi_owner(). | |
*/ | |
mutex_lock(&tsk->futex_exit_mutex); | |
/* | |
* Switch the state to FUTEX_STATE_EXITING under tsk->pi_lock. | |
* | |
* This ensures that all subsequent checks of tsk->futex_state in | |
* attach_to_pi_owner() must observe FUTEX_STATE_EXITING with | |
* tsk->pi_lock held. | |
* | |
* It guarantees also that a pi_state which was queued right before | |
* the state change under tsk->pi_lock by a concurrent waiter must | |
* be observed in exit_pi_state_list(). | |
*/ | |
raw_spin_lock_irq(&tsk->pi_lock); | |
tsk->futex_state = FUTEX_STATE_EXITING; | |
raw_spin_unlock_irq(&tsk->pi_lock); | |
} | |
static void futex_cleanup_end(struct task_struct *tsk, int state) | |
{ | |
/* | |
* Lockless store. The only side effect is that an observer might | |
* take another loop until it becomes visible. | |
*/ | |
tsk->futex_state = state; | |
/* | |
* Drop the exit protection. This unblocks waiters which observed | |
* FUTEX_STATE_EXITING to reevaluate the state. | |
*/ | |
mutex_unlock(&tsk->futex_exit_mutex); | |
} | |
void futex_exec_release(struct task_struct *tsk) | |
{ | |
/* | |
* The state handling is done for consistency, but in the case of | |
* exec() there is no way to prevent futher damage as the PID stays | |
* the same. But for the unlikely and arguably buggy case that a | |
* futex is held on exec(), this provides at least as much state | |
* consistency protection which is possible. | |
*/ | |
futex_cleanup_begin(tsk); | |
futex_cleanup(tsk); | |
/* | |
* Reset the state to FUTEX_STATE_OK. The task is alive and about | |
* exec a new binary. | |
*/ | |
futex_cleanup_end(tsk, FUTEX_STATE_OK); | |
} | |
void futex_exit_release(struct task_struct *tsk) | |
{ | |
futex_cleanup_begin(tsk); | |
futex_cleanup(tsk); | |
futex_cleanup_end(tsk, FUTEX_STATE_DEAD); | |
} | |
long do_futex(u32 __user *uaddr, int op, u32 val, ktime_t *timeout, | |
u32 __user *uaddr2, u32 val2, u32 val3) | |
{ | |
int cmd = op & FUTEX_CMD_MASK; | |
unsigned int flags = 0; | |
if (!(op & FUTEX_PRIVATE_FLAG)) | |
flags |= FLAGS_SHARED; | |
if (op & FUTEX_CLOCK_REALTIME) { | |
flags |= FLAGS_CLOCKRT; | |
if (cmd != FUTEX_WAIT && cmd != FUTEX_WAIT_BITSET && \ | |
cmd != FUTEX_WAIT_REQUEUE_PI) | |
return -ENOSYS; | |
} | |
switch (cmd) { | |
case FUTEX_LOCK_PI: | |
case FUTEX_UNLOCK_PI: | |
case FUTEX_TRYLOCK_PI: | |
case FUTEX_WAIT_REQUEUE_PI: | |
case FUTEX_CMP_REQUEUE_PI: | |
if (!futex_cmpxchg_enabled) | |
return -ENOSYS; | |
} | |
switch (cmd) { | |
case FUTEX_WAIT: | |
val3 = FUTEX_BITSET_MATCH_ANY; | |
fallthrough; | |
case FUTEX_WAIT_BITSET: | |
return futex_wait(uaddr, flags, val, timeout, val3); | |
case FUTEX_WAKE: | |
val3 = FUTEX_BITSET_MATCH_ANY; | |
fallthrough; | |
case FUTEX_WAKE_BITSET: | |
return futex_wake(uaddr, flags, val, val3); | |
case FUTEX_REQUEUE: | |
return futex_requeue(uaddr, flags, uaddr2, val, val2, NULL, 0); | |
case FUTEX_CMP_REQUEUE: | |
return futex_requeue(uaddr, flags, uaddr2, val, val2, &val3, 0); | |
case FUTEX_WAKE_OP: | |
return futex_wake_op(uaddr, flags, uaddr2, val, val2, val3); | |
case FUTEX_LOCK_PI: | |
return futex_lock_pi(uaddr, flags, timeout, 0); | |
case FUTEX_UNLOCK_PI: | |
return futex_unlock_pi(uaddr, flags); | |
case FUTEX_TRYLOCK_PI: | |
return futex_lock_pi(uaddr, flags, NULL, 1); | |
case FUTEX_WAIT_REQUEUE_PI: | |
val3 = FUTEX_BITSET_MATCH_ANY; | |
return futex_wait_requeue_pi(uaddr, flags, val, timeout, val3, | |
uaddr2); | |
case FUTEX_CMP_REQUEUE_PI: | |
return futex_requeue(uaddr, flags, uaddr2, val, val2, &val3, 1); | |
} | |
return -ENOSYS; | |
} | |
SYSCALL_DEFINE6(futex, u32 __user *, uaddr, int, op, u32, val, | |
struct __kernel_timespec __user *, utime, u32 __user *, uaddr2, | |
u32, val3) | |
{ | |
struct timespec64 ts; | |
ktime_t t, *tp = NULL; | |
u32 val2 = 0; | |
int cmd = op & FUTEX_CMD_MASK; | |
if (utime && (cmd == FUTEX_WAIT || cmd == FUTEX_LOCK_PI || | |
cmd == FUTEX_WAIT_BITSET || | |
cmd == FUTEX_WAIT_REQUEUE_PI)) { | |
if (unlikely(should_fail_futex(!(op & FUTEX_PRIVATE_FLAG)))) | |
return -EFAULT; | |
if (get_timespec64(&ts, utime)) | |
return -EFAULT; | |
if (!timespec64_valid(&ts)) | |
return -EINVAL; | |
t = timespec64_to_ktime(ts); | |
if (cmd == FUTEX_WAIT) | |
t = ktime_add_safe(ktime_get(), t); | |
else if (!(op & FUTEX_CLOCK_REALTIME)) | |
t = timens_ktime_to_host(CLOCK_MONOTONIC, t); | |
tp = &t; | |
} | |
/* | |
* requeue parameter in 'utime' if cmd == FUTEX_*_REQUEUE_*. | |
* number of waiters to wake in 'utime' if cmd == FUTEX_WAKE_OP. | |
*/ | |
if (cmd == FUTEX_REQUEUE || cmd == FUTEX_CMP_REQUEUE || | |
cmd == FUTEX_CMP_REQUEUE_PI || cmd == FUTEX_WAKE_OP) | |
val2 = (u32) (unsigned long) utime; | |
return do_futex(uaddr, op, val, tp, uaddr2, val2, val3); | |
} | |
#ifdef CONFIG_COMPAT | |
/* | |
* Fetch a robust-list pointer. Bit 0 signals PI futexes: | |
*/ | |
static inline int | |
compat_fetch_robust_entry(compat_uptr_t *uentry, struct robust_list __user **entry, | |
compat_uptr_t __user *head, unsigned int *pi) | |
{ | |
if (get_user(*uentry, head)) | |
return -EFAULT; | |
*entry = compat_ptr((*uentry) & ~1); | |
*pi = (unsigned int)(*uentry) & 1; | |
return 0; | |
} | |
static void __user *futex_uaddr(struct robust_list __user *entry, | |
compat_long_t futex_offset) | |
{ | |
compat_uptr_t base = ptr_to_compat(entry); | |
void __user *uaddr = compat_ptr(base + futex_offset); | |
return uaddr; | |
} | |
/* | |
* Walk curr->robust_list (very carefully, it's a userspace list!) | |
* and mark any locks found there dead, and notify any waiters. | |
* | |
* We silently return on any sign of list-walking problem. | |
*/ | |
static void compat_exit_robust_list(struct task_struct *curr) | |
{ | |
struct compat_robust_list_head __user *head = curr->compat_robust_list; | |
struct robust_list __user *entry, *next_entry, *pending; | |
unsigned int limit = ROBUST_LIST_LIMIT, pi, pip; | |
unsigned int next_pi; | |
compat_uptr_t uentry, next_uentry, upending; | |
compat_long_t futex_offset; | |
int rc; | |
if (!futex_cmpxchg_enabled) | |
return; | |
/* | |
* Fetch the list head (which was registered earlier, via | |
* sys_set_robust_list()): | |
*/ | |
if (compat_fetch_robust_entry(&uentry, &entry, &head->list.next, &pi)) | |
return; | |
/* | |
* Fetch the relative futex offset: | |
*/ | |
if (get_user(futex_offset, &head->futex_offset)) | |
return; | |
/* | |
* Fetch any possibly pending lock-add first, and handle it | |
* if it exists: | |
*/ | |
if (compat_fetch_robust_entry(&upending, &pending, | |
&head->list_op_pending, &pip)) | |
return; | |
next_entry = NULL; /* avoid warning with gcc */ | |
while (entry != (struct robust_list __user *) &head->list) { | |
/* | |
* Fetch the next entry in the list before calling | |
* handle_futex_death: | |
*/ | |
rc = compat_fetch_robust_entry(&next_uentry, &next_entry, | |
(compat_uptr_t __user *)&entry->next, &next_pi); | |
/* | |
* A pending lock might already be on the list, so | |
* dont process it twice: | |
*/ | |
if (entry != pending) { | |
void __user *uaddr = futex_uaddr(entry, futex_offset); | |
if (handle_futex_death(uaddr, curr, pi, | |
HANDLE_DEATH_LIST)) | |
return; | |
} | |
if (rc) | |
return; | |
uentry = next_uentry; | |
entry = next_entry; | |
pi = next_pi; | |
/* | |
* Avoid excessively long or circular lists: | |
*/ | |
if (!--limit) | |
break; | |
cond_resched(); | |
} | |
if (pending) { | |
void __user *uaddr = futex_uaddr(pending, futex_offset); | |
handle_futex_death(uaddr, curr, pip, HANDLE_DEATH_PENDING); | |
} | |
} | |
COMPAT_SYSCALL_DEFINE2(set_robust_list, | |
struct compat_robust_list_head __user *, head, | |
compat_size_t, len) | |
{ | |
if (!futex_cmpxchg_enabled) | |
return -ENOSYS; | |
if (unlikely(len != sizeof(*head))) | |
return -EINVAL; | |
current->compat_robust_list = head; | |
return 0; | |
} | |
COMPAT_SYSCALL_DEFINE3(get_robust_list, int, pid, | |
compat_uptr_t __user *, head_ptr, | |
compat_size_t __user *, len_ptr) | |
{ | |
struct compat_robust_list_head __user *head; | |
unsigned long ret; | |
struct task_struct *p; | |
if (!futex_cmpxchg_enabled) | |
return -ENOSYS; | |
rcu_read_lock(); | |
ret = -ESRCH; | |
if (!pid) | |
p = current; | |
else { | |
p = find_task_by_vpid(pid); | |
if (!p) | |
goto err_unlock; | |
} | |
ret = -EPERM; | |
if (!ptrace_may_access(p, PTRACE_MODE_READ_REALCREDS)) | |
goto err_unlock; | |
head = p->compat_robust_list; | |
rcu_read_unlock(); | |
if (put_user(sizeof(*head), len_ptr)) | |
return -EFAULT; | |
return put_user(ptr_to_compat(head), head_ptr); | |
err_unlock: | |
rcu_read_unlock(); | |