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/*
* 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!"
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
*/
#include <linux/slab.h>
#include <linux/poll.h>
#include <linux/fs.h>
#include <linux/file.h>
#include <linux/jhash.h>
#include <linux/init.h>
#include <linux/futex.h>
#include <linux/mount.h>
#include <linux/pagemap.h>
#include <linux/syscalls.h>
#include <linux/signal.h>
#include <linux/module.h>
#include <linux/magic.h>
#include <linux/pid.h>
#include <linux/nsproxy.h>
#include <asm/futex.h>
#include "rtmutex_common.h"
int __read_mostly futex_cmpxchg_enabled;
#define FUTEX_HASHBITS (CONFIG_BASE_SMALL ? 4 : 8)
/*
* 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;
atomic_t refcount;
union futex_key key;
};
/*
* We use this hashed waitqueue instead of a normal wait_queue_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 wakup is always to make the first condition true, then
* wake up q->waiter, then make the second condition true.
*/
struct futex_q {
struct plist_node list;
/* Waiter reference */
struct task_struct *task;
/* Which hash list lock to use: */
spinlock_t *lock_ptr;
/* Key which the futex is hashed on: */
union futex_key key;
/* Optional priority inheritance state: */
struct futex_pi_state *pi_state;
/* rt_waiter storage for requeue_pi: */
struct rt_mutex_waiter *rt_waiter;
/* Bitset for the optional bitmasked wakeup */
u32 bitset;
};
/*
* 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 {
spinlock_t lock;
struct plist_head chain;
};
static struct futex_hash_bucket futex_queues[1<<FUTEX_HASHBITS];
/*
* We hash on the keys returned from get_futex_key (see below).
*/
static struct futex_hash_bucket *hash_futex(union futex_key *key)
{
u32 hash = jhash2((u32*)&key->both.word,
(sizeof(key->both.word)+sizeof(key->both.ptr))/4,
key->both.offset);
return &futex_queues[hash & ((1 << FUTEX_HASHBITS)-1)];
}
/*
* 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->both.word == key2->both.word
&& key1->both.ptr == key2->both.ptr
&& key1->both.offset == key2->both.offset);
}
/*
* Take a reference to the resource addressed by a key.
* Can be called while holding spinlocks.
*
*/
static void get_futex_key_refs(union futex_key *key)
{
if (!key->both.ptr)
return;
switch (key->both.offset & (FUT_OFF_INODE|FUT_OFF_MMSHARED)) {
case FUT_OFF_INODE:
atomic_inc(&key->shared.inode->i_count);
break;
case FUT_OFF_MMSHARED:
atomic_inc(&key->private.mm->mm_count);
break;
}
}
/*
* Drop a reference to the resource addressed by a key.
* The hash bucket spinlock must not be held.
*/
static void drop_futex_key_refs(union futex_key *key)
{
if (!key->both.ptr) {
/* If we're here then we tried to put a key we failed to get */
WARN_ON_ONCE(1);
return;
}
switch (key->both.offset & (FUT_OFF_INODE|FUT_OFF_MMSHARED)) {
case FUT_OFF_INODE:
iput(key->shared.inode);
break;
case FUT_OFF_MMSHARED:
mmdrop(key->private.mm);
break;
}
}
/**
* get_futex_key - Get parameters which are the keys for a futex.
* @uaddr: virtual address of the futex
* @fshared: 0 for a PROCESS_PRIVATE futex, 1 for PROCESS_SHARED
* @key: address where result is stored.
* @rw: mapping needs to be read/write (values: VERIFY_READ, VERIFY_WRITE)
*
* Returns a negative error code or 0
* The key words are stored in *key on success.
*
* For shared mappings, it's (page->index, vma->vm_file->f_path.dentry->d_inode,
* offset_within_page). For private mappings, it's (uaddr, current->mm).
* We can usually work out the index without swapping in the page.
*
* lock_page() might sleep, the caller should not hold a spinlock.
*/
static int
get_futex_key(u32 __user *uaddr, int fshared, union futex_key *key, int rw)
{
unsigned long address = (unsigned long)uaddr;
struct mm_struct *mm = current->mm;
struct page *page;
int err;
/*
* 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;
/*
* 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) {
if (unlikely(!access_ok(rw, uaddr, sizeof(u32))))
return -EFAULT;
key->private.mm = mm;
key->private.address = address;
get_futex_key_refs(key);
return 0;
}
again:
err = get_user_pages_fast(address, 1, rw == VERIFY_WRITE, &page);
if (err < 0)
return err;
page = compound_head(page);
lock_page(page);
if (!page->mapping) {
unlock_page(page);
put_page(page);
goto again;
}
/*
* Private mappings are handled in a simple way.
*
* 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)) {
key->both.offset |= FUT_OFF_MMSHARED; /* ref taken on mm */
key->private.mm = mm;
key->private.address = address;
} else {
key->both.offset |= FUT_OFF_INODE; /* inode-based key */
key->shared.inode = page->mapping->host;
key->shared.pgoff = page->index;
}
get_futex_key_refs(key);
unlock_page(page);
put_page(page);
return 0;
}
static inline
void put_futex_key(int fshared, union futex_key *key)
{
drop_futex_key_refs(key);
}
/*
* 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)
{
int ret = get_user_pages(current, current->mm, (unsigned long)uaddr,
1, 1, 0, NULL, NULL);
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 u32 cmpxchg_futex_value_locked(u32 __user *uaddr, u32 uval, u32 newval)
{
u32 curval;
pagefault_disable();
curval = futex_atomic_cmpxchg_inatomic(uaddr, uval, newval);
pagefault_enable();
return curval;
}
static int get_futex_value_locked(u32 *dest, u32 __user *from)
{
int ret;
pagefault_disable();
ret = __copy_from_user_inatomic(dest, from, sizeof(u32));
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;
atomic_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 free_pi_state(struct futex_pi_state *pi_state)
{
if (!atomic_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) {
spin_lock_irq(&pi_state->owner->pi_lock);
list_del_init(&pi_state->list);
spin_unlock_irq(&pi_state->owner->pi_lock);
rt_mutex_proxy_unlock(&pi_state->pi_mutex, pi_state->owner);
}
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;
atomic_set(&pi_state->refcount, 1);
current->pi_state_cache = pi_state;
}
}
/*
* Look up the task based on what TID userspace gave us.
* We dont trust it.
*/
static struct task_struct * futex_find_get_task(pid_t pid)
{
struct task_struct *p;
const struct cred *cred = current_cred(), *pcred;
rcu_read_lock();
p = find_task_by_vpid(pid);
if (!p) {
p = ERR_PTR(-ESRCH);
} else {
pcred = __task_cred(p);
if (cred->euid != pcred->euid &&
cred->euid != pcred->uid)
p = ERR_PTR(-ESRCH);
else
get_task_struct(p);
}
rcu_read_unlock();
return p;
}
/*
* 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.)
*/
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:
*/
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);
spin_unlock_irq(&curr->pi_lock);
spin_lock(&hb->lock);
spin_lock_irq(&curr->pi_lock);
/*
* We dropped the pi-lock, so re-check whether this
* task still owns the PI-state:
*/
if (head->next != next) {
spin_unlock(&hb->lock);
continue;
}
WARN_ON(pi_state->owner != curr);
WARN_ON(list_empty(&pi_state->list));
list_del_init(&pi_state->list);
pi_state->owner = NULL;
spin_unlock_irq(&curr->pi_lock);
rt_mutex_unlock(&pi_state->pi_mutex);
spin_unlock(&hb->lock);
spin_lock_irq(&curr->pi_lock);
}
spin_unlock_irq(&curr->pi_lock);
}
static int
lookup_pi_state(u32 uval, struct futex_hash_bucket *hb,
union futex_key *key, struct futex_pi_state **ps)
{
struct futex_pi_state *pi_state = NULL;
struct futex_q *this, *next;
struct plist_head *head;
struct task_struct *p;
pid_t pid = uval & FUTEX_TID_MASK;
head = &hb->chain;
plist_for_each_entry_safe(this, next, head, list) {
if (match_futex(&this->key, key)) {
/*
* Another waiter already exists - bump up
* the refcount and return its pi_state:
*/
pi_state = this->pi_state;
/*
* Userspace might have messed up non PI and PI futexes
*/
if (unlikely(!pi_state))
return -EINVAL;
WARN_ON(!atomic_read(&pi_state->refcount));
WARN_ON(pid && pi_state->owner &&
pi_state->owner->pid != pid);
atomic_inc(&pi_state->refcount);
*ps = pi_state;
return 0;
}
}
/*
* 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
*/
if (!pid)
return -ESRCH;
p = futex_find_get_task(pid);
if (IS_ERR(p))
return PTR_ERR(p);
/*
* We need to look at the task state flags to figure out,
* whether the task is exiting. To protect against the do_exit
* change of the task flags, we do this protected by
* p->pi_lock:
*/
spin_lock_irq(&p->pi_lock);
if (unlikely(p->flags & PF_EXITING)) {
/*
* The task is on the way out. When PF_EXITPIDONE is
* set, we know that the task has finished the
* cleanup:
*/
int ret = (p->flags & PF_EXITPIDONE) ? -ESRCH : -EAGAIN;
spin_unlock_irq(&p->pi_lock);
put_task_struct(p);
return ret;
}
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);
pi_state->owner = p;
spin_unlock_irq(&p->pi_lock);
put_task_struct(p);
*ps = pi_state;
return 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.
* @set_waiters: force setting the FUTEX_WAITERS bit (1) or not (0)
*
* Returns:
* 0 - ready to wait
* 1 - acquired the lock
* <0 - error
*
* The hb->lock and futex_key refs shall be held by the caller.
*/
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, int set_waiters)
{
int lock_taken, ret, ownerdied = 0;
u32 uval, newval, curval;
retry:
ret = lock_taken = 0;
/*
* To avoid races, we attempt to take the lock here again
* (by doing a 0 -> TID atomic cmpxchg), while holding all
* the locks. It will most likely not succeed.
*/
newval = task_pid_vnr(task);
if (set_waiters)
newval |= FUTEX_WAITERS;
curval = cmpxchg_futex_value_locked(uaddr, 0, newval);
if (unlikely(curval == -EFAULT))
return -EFAULT;
/*
* Detect deadlocks.
*/
if ((unlikely((curval & FUTEX_TID_MASK) == task_pid_vnr(task))))
return -EDEADLK;
/*
* Surprise - we got the lock. Just return to userspace:
*/
if (unlikely(!curval))
return 1;
uval = curval;
/*
* Set the FUTEX_WAITERS flag, so the owner will know it has someone
* to wake at the next unlock.
*/
newval = curval | FUTEX_WAITERS;
/*
* There are two cases, where a futex might have no owner (the
* owner TID is 0): OWNER_DIED. We take over the futex in this
* case. We also do an unconditional take over, when the owner
* of the futex died.
*
* This is safe as we are protected by the hash bucket lock !
*/
if (unlikely(ownerdied || !(curval & FUTEX_TID_MASK))) {
/* Keep the OWNER_DIED bit */
newval = (curval & ~FUTEX_TID_MASK) | task_pid_vnr(task);
ownerdied = 0;
lock_taken = 1;
}
curval = cmpxchg_futex_value_locked(uaddr, uval, newval);
if (unlikely(curval == -EFAULT))
return -EFAULT;
if (unlikely(curval != uval))
goto retry;
/*
* We took the lock due to owner died take over.
*/
if (unlikely(lock_taken))
return 1;
/*
* We dont have the lock. Look up the PI state (or create it if
* we are the first waiter):
*/
ret = lookup_pi_state(uval, hb, key, ps);
if (unlikely(ret)) {
switch (ret) {
case -ESRCH:
/*
* No owner found for this futex. Check if the
* OWNER_DIED bit is set to figure out whether
* this is a robust futex or not.
*/
if (get_futex_value_locked(&curval, uaddr))
return -EFAULT;
/*
* We simply start over in case of a robust
* futex. The code above will take the futex
* and return happy.
*/
if (curval & FUTEX_OWNER_DIED) {
ownerdied = 1;
goto retry;
}
default:
break;
}
}
return ret;
}
/*
* The hash bucket lock must be held when this is called.
* Afterwards, the futex_q must not be accessed.
*/
static void wake_futex(struct futex_q *q)
{
struct task_struct *p = q->task;
/*
* We set q->lock_ptr = NULL _before_ we wake up the task. If
* a non futex wake up happens on another CPU then the task
* might exit and p would dereference a non existing task
* struct. Prevent this by holding a reference on p across the
* wake up.
*/
get_task_struct(p);
plist_del(&q->list, &q->list.plist);
/*
* The waiting task can free the futex_q as soon as
* q->lock_ptr = NULL is written, without taking any locks. A
* memory barrier is required here to prevent the following
* store to lock_ptr from getting ahead of the plist_del.
*/
smp_wmb();
q->lock_ptr = NULL;
wake_up_state(p, TASK_NORMAL);
put_task_struct(p);
}
static int wake_futex_pi(u32 __user *uaddr, u32 uval, struct futex_q *this)
{
struct task_struct *new_owner;
struct futex_pi_state *pi_state = this->pi_state;
u32 curval, newval;
if (!pi_state)
return -EINVAL;
spin_lock(&pi_state->pi_mutex.wait_lock);
new_owner = rt_mutex_next_owner(&pi_state->pi_mutex);
/*
* This happens when we have stolen the lock and the original
* pending owner did not enqueue itself back on the rt_mutex.
* Thats not a tragedy. We know that way, that a lock waiter
* is on the fly. We make the futex_q waiter the pending owner.
*/
if (!new_owner)
new_owner = this->task;
/*
* We pass it to the next owner. (The WAITERS bit is always
* kept enabled while there is PI state around. We must also
* preserve the owner died bit.)
*/
if (!(uval & FUTEX_OWNER_DIED)) {
int ret = 0;
newval = FUTEX_WAITERS | task_pid_vnr(new_owner);
curval = cmpxchg_futex_value_locked(uaddr, uval, newval);
if (curval == -EFAULT)
ret = -EFAULT;
else if (curval != uval)
ret = -EINVAL;
if (ret) {
spin_unlock(&pi_state->pi_mutex.wait_lock);
return ret;
}
}
spin_lock_irq(&pi_state->owner->pi_lock);
WARN_ON(list_empty(&pi_state->list));
list_del_init(&pi_state->list);
spin_unlock_irq(&pi_state->owner->pi_lock);
spin_lock_irq(&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;
spin_unlock_irq(&new_owner->pi_lock);
spin_unlock(&pi_state->pi_mutex.wait_lock);
rt_mutex_unlock(&pi_state->pi_mutex);
return 0;
}
static int unlock_futex_pi(u32 __user *uaddr, u32 uval)
{
u32 oldval;
/*
* There is no waiter, so we unlock the futex. The owner died
* bit has not to be preserved here. We are the owner:
*/
oldval = cmpxchg_futex_value_locked(uaddr, uval, 0);
if (oldval == -EFAULT)
return oldval;
if (oldval != uval)
return -EAGAIN;
return 0;
}
/*
* 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, int fshared, int nr_wake, u32 bitset)
{
struct futex_hash_bucket *hb;
struct futex_q *this, *next;
struct plist_head *head;
union futex_key key = FUTEX_KEY_INIT;
int ret;
if (!bitset)
return -EINVAL;
ret = get_futex_key(uaddr, fshared, &key, VERIFY_READ);
if (unlikely(ret != 0))
goto out;
hb = hash_futex(&key);
spin_lock(&hb->lock);
head = &hb->chain;
plist_for_each_entry_safe(this, next, head, 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;
wake_futex(this);
if (++ret >= nr_wake)
break;
}
}
spin_unlock(&hb->lock);
put_futex_key(fshared, &key);
out:
return ret;
}
/*
* Wake up all waiters hashed on the physical page that is mapped
* to this virtual address:
*/
static int
futex_wake_op(u32 __user *uaddr1, int fshared, 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 plist_head *head;
struct futex_q *this, *next;
int ret, op_ret;
retry:
ret = get_futex_key(uaddr1, fshared, &key1, VERIFY_READ);
if (unlikely(ret != 0))
goto out;
ret = get_futex_key(uaddr2, fshared, &key2, VERIFY_WRITE);
if (unlikely(ret != 0))
goto out_put_key1;
hb1 = hash_futex(&key1);
hb2 = hash_futex(&key2);
double_lock_hb(hb1, hb2);
retry_private:
op_ret = futex_atomic_op_inuser(op, uaddr2);
if (unlikely(op_ret < 0)) {
double_unlock_hb(hb1, hb2);
#ifndef CONFIG_MMU
/*
* 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;
goto out_put_keys;
#endif
if (unlikely(op_ret != -EFAULT)) {
ret = op_ret;
goto out_put_keys;
}
ret = fault_in_user_writeable(uaddr2);
if (ret)
goto out_put_keys;
if (!fshared)
goto retry_private;
put_futex_key(fshared, &key2);
put_futex_key(fshared, &key1);
goto retry;
}
head = &hb1->chain;
plist_for_each_entry_safe(this, next, head, list) {
if (match_futex (&this->key, &key1)) {
wake_futex(this);
if (++ret >= nr_wake)
break;
}
}
if (op_ret > 0) {
head = &hb2->chain;
op_ret = 0;
plist_for_each_entry_safe(this, next, head, list) {
if (match_futex (&this->key, &key2)) {
wake_futex(this);
if (++op_ret >= nr_wake2)
break;
}
}
ret += op_ret;
}
double_unlock_hb(hb1, hb2);
out_put_keys:
put_futex_key(fshared, &key2);
out_put_key1:
put_futex_key(fshared, &key1);
out:
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);
plist_add(&q->list, &hb2->chain);
q->lock_ptr = &hb2->lock;
#ifdef CONFIG_DEBUG_PI_LIST
q->list.plist.lock = &hb2->lock;
#endif
}
get_futex_key_refs(key2);
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)
{
drop_futex_key_refs(&q->key);
get_futex_key_refs(key);
q->key = *key;
WARN_ON(plist_node_empty(&q->list));
plist_del(&q->list, &q->list.plist);
WARN_ON(!q->rt_waiter);
q->rt_waiter = NULL;
q->lock_ptr = &hb->lock;
#ifdef CONFIG_DEBUG_PI_LIST
q->list.plist.lock = &hb->lock;
#endif
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
* @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.
*
* Returns:
* 0 - failed to acquire the lock atomicly
* 1 - acquired the lock
* <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, int set_waiters)
{
struct futex_q *top_waiter = NULL;
u32 curval;
int ret;
if (get_futex_value_locked(&curval, pifutex))
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;
/*
* 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.
*/
ret = futex_lock_pi_atomic(pifutex, hb2, key2, ps, top_waiter->task,
set_waiters);
if (ret == 1)
requeue_pi_wake_futex(top_waiter, key2, hb2);
return ret;
}
/**
* futex_requeue() - Requeue waiters from uaddr1 to uaddr2
* uaddr1: source futex user address
* 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)
* 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.
*
* Returns:
* >=0 - on success, the number of tasks requeued or woken
* <0 - on error
*/
static int futex_requeue(u32 __user *uaddr1, int fshared, 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 drop_count = 0, task_count = 0, ret;
struct futex_pi_state *pi_state = NULL;
struct futex_hash_bucket *hb1, *hb2;
struct plist_head *head1;
struct futex_q *this, *next;
u32 curval2;
if (requeue_pi) {
/*
* 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:
if (pi_state != NULL) {
/*
* We will have to lookup the pi_state again, so free this one
* to keep the accounting correct.
*/
free_pi_state(pi_state);
pi_state = NULL;
}
ret = get_futex_key(uaddr1, fshared, &key1, VERIFY_READ);
if (unlikely(ret != 0))
goto out;
ret = get_futex_key(uaddr2, fshared, &key2,
requeue_pi ? VERIFY_WRITE : VERIFY_READ);
if (unlikely(ret != 0))
goto out_put_key1;
hb1 = hash_futex(&key1);
hb2 = hash_futex(&key2);
retry_private:
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);
ret = get_user(curval, uaddr1);
if (ret)
goto out_put_keys;
if (!fshared)
goto retry_private;
put_futex_key(fshared, &key2);
put_futex_key(fshared, &key1);
goto retry;
}
if (curval != *cmpval) {
ret = -EAGAIN;
goto out_unlock;
}
}
if (requeue_pi && (task_count - nr_wake < nr_requeue)) {
/*
* 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, 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 (ret == 1) {
WARN_ON(pi_state);
task_count++;
ret = get_futex_value_locked(&curval2, uaddr2);
if (!ret)
ret = lookup_pi_state(curval2, hb2, &key2,
&pi_state);
}
switch (ret) {
case 0:
break;
case -EFAULT:
double_unlock_hb(hb1, hb2);
put_futex_key(fshared, &key2);
put_futex_key(fshared, &key1);
ret = fault_in_user_writeable(uaddr2);
if (!ret)
goto retry;
goto out;
case -EAGAIN:
/* The owner was exiting, try again. */
double_unlock_hb(hb1, hb2);
put_futex_key(fshared, &key2);
put_futex_key(fshared, &key1);
cond_resched();
goto retry;
default:
goto out_unlock;
}
}
head1 = &hb1->chain;
plist_for_each_entry_safe(this, next, head1, 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.
*/
if ((requeue_pi && !this->rt_waiter) ||
(!requeue_pi && this->rt_waiter)) {
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) {
wake_futex(this);
continue;
}
/*
* 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. */
atomic_inc(&pi_state->refcount);
this->pi_state = pi_state;
ret = rt_mutex_start_proxy_lock(&pi_state->pi_mutex,
this->rt_waiter,
this->task, 1);
if (ret == 1) {
/* We got the lock. */
requeue_pi_wake_futex(this, &key2, hb2);
continue;
} else if (ret) {
/* -EDEADLK */
this->pi_state = NULL;
free_pi_state(pi_state);
goto out_unlock;
}
}
requeue_futex(this, hb1, hb2, &key2);
drop_count++;
}
out_unlock:
double_unlock_hb(hb1, hb2);
/*
* drop_futex_key_refs() must be called outside the spinlocks. During
* the requeue we moved futex_q's from the hash bucket at key1 to the
* one at key2 and updated their key pointer. We no longer need to
* hold the references to key1.
*/
while (--drop_count >= 0)
drop_futex_key_refs(&key1);
out_put_keys:
put_futex_key(fshared, &key2);
out_put_key1:
put_futex_key(fshared, &key1);
out:
if (pi_state != NULL)
free_pi_state(pi_state);
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)
{
struct futex_hash_bucket *hb;
get_futex_key_refs(&q->key);
hb = hash_futex(&q->key);
q->lock_ptr = &hb->lock;
spin_lock(&hb->lock);
return 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);
#ifdef CONFIG_DEBUG_PI_LIST
q->list.plist.lock = &hb->lock;
#endif
plist_add(&q->list, &hb->chain);
q->task = current;
spin_unlock(&hb->lock);
}
static inline void
queue_unlock(struct futex_q *q, struct futex_hash_bucket *hb)
{
spin_unlock(&hb->lock);
drop_futex_key_refs(&q->key);
}
/*
* queue_me and unqueue_me must be called as a pair, each
* exactly once. They are called with the hashed spinlock held.
*/
/* Return 1 if we were still queued (ie. 0 means we were woken) */
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:
lock_ptr = q->lock_ptr;
barrier();
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;
}
WARN_ON(plist_node_empty(&q->list));
plist_del(&q->list, &q->list.plist);
BUG_ON(q->pi_state);
spin_unlock(lock_ptr);
ret = 1;
}
drop_futex_key_refs(&q->key);
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)
{
WARN_ON(plist_node_empty(&q->list));
plist_del(&q->list, &q->list.plist);
BUG_ON(!q->pi_state);
free_pi_state(q->pi_state);
q->pi_state = NULL;
spin_unlock(q->lock_ptr);
drop_futex_key_refs(&q->key);
}
/*
* Fixup the pi_state owner with the new owner.
*
* Must be called with hash bucket lock held and mm->sem held for non
* private futexes.
*/
static int fixup_pi_state_owner(u32 __user *uaddr, struct futex_q *q,
struct task_struct *newowner, int fshared)
{
u32 newtid = task_pid_vnr(newowner) | FUTEX_WAITERS;
struct futex_pi_state *pi_state = q->pi_state;
struct task_struct *oldowner = pi_state->owner;
u32 uval, curval, newval;
int ret;
/* Owner died? */
if (!pi_state->owner)
newtid |= FUTEX_OWNER_DIED;
/*
* We are here either because we stole the rtmutex from the
* pending owner or we are the pending owner which failed to
* get the rtmutex. We have to replace the pending owner 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 hash bucket lock to
* handle the fault. This might be observed in the PID check
* in lookup_pi_state.
*/
retry:
if (get_futex_value_locked(&uval, uaddr))
goto handle_fault;
while (1) {
newval = (uval & FUTEX_OWNER_DIED) | newtid;
curval = cmpxchg_futex_value_locked(uaddr, uval, newval);
if (curval == -EFAULT)
goto handle_fault;
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) {
spin_lock_irq(&pi_state->owner->pi_lock);
WARN_ON(list_empty(&pi_state->list));
list_del_init(&pi_state->list);
spin_unlock_irq(&pi_state->owner->pi_lock);
}
pi_state->owner = newowner;
spin_lock_irq(&newowner->pi_lock);
WARN_ON(!list_empty(&pi_state->list));
list_add(&pi_state->list, &newowner->pi_state_list);
spin_unlock_irq(&newowner->pi_lock);
return 0;
/*
* To handle the page fault we need to drop the hash bucket
* lock here. That gives the other task (either the pending
* owner 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 hash bucket lock and before trying to
* do another fixup. When the fixup has been done already we
* simply return.
*/
handle_fault:
spin_unlock(q->lock_ptr);
ret = fault_in_user_writeable(uaddr);
spin_lock(q->lock_ptr);
/*
* Check if someone else fixed it for us:
*/
if (pi_state->owner != oldowner)
return 0;
if (ret)
return ret;
goto retry;
}
/*
* In case we must use restart_block to restart a futex_wait,
* we encode in the 'flags' shared capability
*/
#define FLAGS_SHARED 0x01
#define FLAGS_CLOCKRT 0x02
#define FLAGS_HAS_TIMEOUT 0x04
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
* @fshared: whether the futex is shared (1) or not (0)
* @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.
*
* Returns:
* 1 - success, lock taken
* 0 - success, lock not taken
* <0 - on error (-EFAULT)
*/
static int fixup_owner(u32 __user *uaddr, int fshared, struct futex_q *q,
int locked)
{
struct task_struct *owner;
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:
*/
if (q->pi_state->owner != current)
ret = fixup_pi_state_owner(uaddr, q, current, fshared);
goto out;
}
/*
* Catch the rare case, where the lock was released when we were on the
* way back before we locked the hash bucket.
*/
if (q->pi_state->owner == current) {
/*
* Try to get the rt_mutex now. This might fail as some other
* task acquired the rt_mutex after we removed ourself from the
* rt_mutex waiters list.
*/
if (rt_mutex_trylock(&q->pi_state->pi_mutex)) {
locked = 1;
goto out;
}
/*
* pi_state is incorrect, some other task did a lock steal and
* we returned due to timeout or signal without taking the
* rt_mutex. Too late. We can access the rt_mutex_owner without
* locking, as the other task is now blocked on the hash bucket
* lock. Fix the state up.
*/
owner = rt_mutex_owner(&q->pi_state->pi_mutex);
ret = fixup_pi_state_owner(uaddr, q, owner, fshared);
goto out;
}
/*
* Paranoia check. If we did not take the lock, then we should not be
* the owner, nor the pending 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);
out:
return ret ? ret : locked;
}
/**
* 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)
{
queue_me(q, hb);
/*
* There might have been scheduling since the queue_me(), as we
* cannot hold a spinlock across the get_user() in case it
* faults, and we cannot just set TASK_INTERRUPTIBLE state when
* queueing ourselves into the futex hash. This code thus has to
* rely on the futex_wake() code removing us from hash when it
* wakes us up.
*/
set_current_state(TASK_INTERRUPTIBLE);
/* Arm the timer */
if (timeout) {
hrtimer_start_expires(&timeout->timer, HRTIMER_MODE_ABS);
if (!hrtimer_active(&timeout->timer))
timeout->task = NULL;
}
/*
* !plist_node_empty() is safe here without any lock.
* q.lock_ptr != 0 is not safe, because of ordering against wakeup.
*/
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)
schedule();
}
__set_current_state(TASK_RUNNING);
}
/**
* futex_wait_setup() - Prepare to wait on a futex
* @uaddr: the futex userspace address
* @val: the expected value
* @fshared: whether the futex is shared (1) or not (0)
* @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.
*
* Returns:
* 0 - uaddr contains val and hb has been locked
* <1 - -EFAULT or -EWOULDBLOCK (uaddr does not contain val) and hb is unlcoked
*/
static int futex_wait_setup(u32 __user *uaddr, u32 val, int fshared,
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 queued after testing *uaddr, that would open
* a race condition where we could block indefinitely with
* cond(var) false, which would violate the guarantee.
*
* A consequence is that futex_wait() can return zero and absorb
* a wakeup when *uaddr != val on entry to the syscall. This is
* rare, but normal.
*/
retry:
q->key = FUTEX_KEY_INIT;
ret = get_futex_key(uaddr, fshared, &q->key, VERIFY_READ);
if (unlikely(ret != 0))
return ret;
retry_private:
*hb = queue_lock(q);
ret = get_futex_value_locked(&uval, uaddr);
if (ret) {
queue_unlock(q, *hb);
ret = get_user(uval, uaddr);
if (ret)
goto out;
if (!fshared)
goto retry_private;
put_futex_key(fshared, &q->key);
goto retry;
}
if (uval != val) {
queue_unlock(q, *hb);
ret = -EWOULDBLOCK;
}
out:
if (ret)
put_futex_key(fshared, &q->key);
return ret;
}
static int futex_wait(u32 __user *uaddr, int fshared,
u32 val, ktime_t *abs_time, u32 bitset, int clockrt)
{
struct hrtimer_sleeper timeout, *to = NULL;
struct restart_block *restart;
struct futex_hash_bucket *hb;
struct futex_q q;
int ret;
if (!bitset)
return -EINVAL;
q.pi_state = NULL;
q.bitset = bitset;
q.rt_waiter = NULL;
if (abs_time) {
to = &timeout;
hrtimer_init_on_stack(&to->timer, clockrt ? CLOCK_REALTIME :
CLOCK_MONOTONIC, HRTIMER_MODE_ABS);
hrtimer_init_sleeper(to, current);
hrtimer_set_expires_range_ns(&to->timer, *abs_time,
current->timer_slack_ns);
}
/* Prepare to wait on uaddr. */
ret = futex_wait_setup(uaddr, val, fshared, &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;
if (!unqueue_me(&q))
goto out_put_key;
ret = -ETIMEDOUT;
if (to && !to->task)
goto out_put_key;
/*
* We expect signal_pending(current), but another thread may
* have handled it for us already.
*/
ret = -ERESTARTSYS;
if (!abs_time)
goto out_put_key;
restart = &current_thread_info()->restart_block;
restart->fn = futex_wait_restart;
restart->futex.uaddr = (u32 *)uaddr;
restart->futex.val = val;
restart->futex.time = abs_time->tv64;
restart->futex.bitset = bitset;
restart->futex.flags = FLAGS_HAS_TIMEOUT;
if (fshared)
restart->futex.flags |= FLAGS_SHARED;
if (clockrt)
restart->futex.flags |= FLAGS_CLOCKRT;
ret = -ERESTART_RESTARTBLOCK;
out_put_key:
put_futex_key(fshared, &q.key);
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 = (u32 __user *)restart->futex.uaddr;
int fshared = 0;
ktime_t t, *tp = NULL;
if (restart->futex.flags & FLAGS_HAS_TIMEOUT) {
t.tv64 = restart->futex.time;
tp = &t;
}
restart->fn = do_no_restart_syscall;
if (restart->futex.flags & FLAGS_SHARED)
fshared = 1;
return (long)futex_wait(uaddr, fshared, restart->futex.val, tp,
restart->futex.bitset,
restart->futex.flags & FLAGS_CLOCKRT);
}
/*
* 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, it does PI, etc. (Due to
* races the kernel might see a 0 value of the futex too.)
*/
static int futex_lock_pi(u32 __user *uaddr, int fshared,
int detect, ktime_t *time, int trylock)
{
struct hrtimer_sleeper timeout, *to = NULL;
struct futex_hash_bucket *hb;
struct futex_q q;
int res, ret;
if (refill_pi_state_cache())
return -ENOMEM;
if (time) {
to = &timeout;
hrtimer_init_on_stack(&to->timer, CLOCK_REALTIME,
HRTIMER_MODE_ABS);
hrtimer_init_sleeper(to, current);
hrtimer_set_expires(&to->timer, *time);
}
q.pi_state = NULL;
q.rt_waiter = NULL;
retry:
q.key = FUTEX_KEY_INIT;
ret = get_futex_key(uaddr, fshared, &q.key, VERIFY_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, 0);
if (unlikely(ret)) {
switch (ret) {
case 1:
/* We got the lock. */
ret = 0;
goto out_unlock_put_key;
case -EFAULT:
goto uaddr_faulted;
case -EAGAIN:
/*
* Task is exiting and we just wait for the
* exit to complete.
*/
queue_unlock(&q, hb);
put_futex_key(fshared, &q.key);
cond_resched();
goto retry;
default:
goto out_unlock_put_key;
}
}
/*
* Only actually queue now that the atomic ops are done:
*/
queue_me(&q, hb);
WARN_ON(!q.pi_state);
/*
* Block on the PI mutex:
*/
if (!trylock)
ret = rt_mutex_timed_lock(&q.pi_state->pi_mutex, to, 1);
else {
ret = rt_mutex_trylock(&q.pi_state->pi_mutex);
/* Fixup the trylock return value: */
ret = ret ? 0 : -EWOULDBLOCK;
}
spin_lock(q.lock_ptr);
/*
* Fixup the pi_state owner and possibly acquire the lock if we
* haven't already.
*/
res = fixup_owner(uaddr, fshared, &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))
rt_mutex_unlock(&q.pi_state->pi_mutex);
/* Unqueue and drop the lock */
unqueue_me_pi(&q);
goto out;
out_unlock_put_key:
queue_unlock(&q, hb);
out_put_key:
put_futex_key(fshared, &q.key);
out:
if (to)
destroy_hrtimer_on_stack(&to->timer);
return ret != -EINTR ? ret : -ERESTARTNOINTR;
uaddr_faulted:
queue_unlock(&q, hb);
ret = fault_in_user_writeable(uaddr);
if (ret)
goto out_put_key;
if (!fshared)
goto retry_private;
put_futex_key(fshared, &q.key);
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, int fshared)
{
struct futex_hash_bucket *hb;
struct futex_q *this, *next;
u32 uval;
struct plist_head *head;
union futex_key key = FUTEX_KEY_INIT;
int ret;
retry:
if (get_user(uval, uaddr))
return -EFAULT;
/*
* We release only a lock we actually own:
*/
if ((uval & FUTEX_TID_MASK) != task_pid_vnr(current))
return -EPERM;
ret = get_futex_key(uaddr, fshared, &key, VERIFY_WRITE);
if (unlikely(ret != 0))
goto out;
hb = hash_futex(&key);
spin_lock(&hb->lock);
/*
* To avoid races, try to do the TID -> 0 atomic transition
* again. If it succeeds then we can return without waking
* anyone else up:
*/
if (!(uval & FUTEX_OWNER_DIED))
uval = cmpxchg_futex_value_locked(uaddr, task_pid_vnr(current), 0);
if (unlikely(uval == -EFAULT))
goto pi_faulted;
/*
* Rare case: we managed to release the lock atomically,
* no need to wake anyone else up:
*/
if (unlikely(uval == task_pid_vnr(current)))
goto out_unlock;
/*
* Ok, other tasks may need to be woken up - check waiters
* and do the wakeup if necessary:
*/
head = &hb->chain;
plist_for_each_entry_safe(this, next, head, list) {
if (!match_futex (&this->key, &key))
continue;
ret = wake_futex_pi(uaddr, uval, this);
/*
* The atomic access to the futex value
* generated a pagefault, so retry the
* user-access and the wakeup:
*/
if (ret == -EFAULT)
goto pi_faulted;
goto out_unlock;
}
/*
* No waiters - kernel unlocks the futex:
*/
if (!(uval & FUTEX_OWNER_DIED)) {
ret = unlock_futex_pi(uaddr, uval);
if (ret == -EFAULT)
goto pi_faulted;
}
out_unlock:
spin_unlock(&hb->lock);
put_futex_key(fshared, &key);
out:
return ret;
pi_faulted:
spin_unlock(&hb->lock);
put_futex_key(fshared, &key);
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.
*
* Returns
* 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, &q->list.plist);
drop_futex_key_refs(&q->key);
if (timeout && !timeout->task)
ret = -ETIMEDOUT;
else
ret = -ERESTARTNOINTR;
}
return ret;
}
/**
* futex_wait_requeue_pi() - Wait on uaddr and take uaddr2
* @uaddr: the futex we initialyl wait on (non-pi)
* @fshared: whether the futexes are shared (1) or not (0). 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.
* @clockrt: whether to use CLOCK_REALTIME (1) or CLOCK_MONOTONIC (0)
* @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. 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 wouldn't 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 and subsequent unlock
* 3) signal (before or after requeue)
* 4) timeout (before or after requeue)
*
* If 3, we setup a restart_block with futex_wait_requeue_pi() as the function.
*
* 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, we setup a restart_block with futex_lock_pi() as the function.
*
* If 4 or 7, we cleanup and return with -ETIMEDOUT.
*
* Returns:
* 0 - On success
* <0 - On error
*/
static int futex_wait_requeue_pi(u32 __user *uaddr, int fshared,
u32 val, ktime_t *abs_time, u32 bitset,
int clockrt, u32 __user *uaddr2)
{
struct hrtimer_sleeper timeout, *to = NULL;
struct rt_mutex_waiter rt_waiter;
struct rt_mutex *pi_mutex = NULL;
struct futex_hash_bucket *hb;
union futex_key key2;
struct futex_q q;
int res, ret;
if (!bitset)
return -EINVAL;
if (abs_time) {
to = &timeout;
hrtimer_init_on_stack(&to->timer, clockrt ? CLOCK_REALTIME :
CLOCK_MONOTONIC, HRTIMER_MODE_ABS);
hrtimer_init_sleeper(to, current);
hrtimer_set_expires_range_ns(&to->timer, *abs_time,
current->timer_slack_ns);
}
/*
* The waiter is allocated on our stack, manipulated by the requeue
* code while we sleep on uaddr.
*/
debug_rt_mutex_init_waiter(&rt_waiter);
rt_waiter.task = NULL;
q.pi_state = NULL;
q.bitset = bitset;
q.rt_waiter = &rt_waiter;
key2 = FUTEX_KEY_INIT;
ret = get_futex_key(uaddr2, fshared, &key2, VERIFY_WRITE);
if (unlikely(ret != 0))
goto out;
/* Prepare to wait on uaddr. */
ret = futex_wait_setup(uaddr, val, fshared, &q, &hb);
if (ret)
goto out_key2;
/* 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_put_keys;
/*
* 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 acquition by the requeue code.
*/
/* 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,
fshared);
spin_unlock(q.lock_ptr);
}
} else {
/*
* 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_finish_proxy_lock(pi_mutex, to, &rt_waiter, 1);
debug_rt_mutex_free_waiter(&rt_waiter);
spin_lock(q.lock_ptr);
/*
* Fixup the pi_state owner and possibly acquire the lock if we
* haven't already.
*/
res = fixup_owner(uaddr2, fshared, &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;
/* Unqueue and drop the lock. */
unqueue_me_pi(&q);
}
/*
* 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 == -EFAULT) {
if (rt_mutex_owner(pi_mutex) == current)
rt_mutex_unlock(pi_mutex);
} else if (ret == -EINTR) {
/*
* We've already been requeued, but we have no way to
* restart by calling futex_lock_pi() directly. We
* could restart the syscall, but that will look at
* the user space value and return right away. So we
* drop back with EWOULDBLOCK to tell user space that
* "val" has been changed. That's the same what the
* restart of the syscall would do in
* futex_wait_setup().
*/
ret = -EWOULDBLOCK;
}
out_put_keys:
put_futex_key(fshared, &q.key);
out_key2:
put_futex_key(fshared, &key2);
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;
const struct cred *cred = current_cred(), *pcred;
if (!futex_cmpxchg_enabled)
return -ENOSYS;
if (!pid)
head = current->robust_list;
else {
struct task_struct *p;
ret = -ESRCH;
rcu_read_lock();
p = find_task_by_vpid(pid);
if (!p)
goto err_unlock;
ret = -EPERM;
pcred = __task_cred(p);
if (cred->euid != pcred->euid &&
cred->euid != pcred->uid &&
!capable(CAP_SYS_PTRACE))
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;
}
/*
* Process a futex-list entry, check whether it's owned by the
* dying task, and do notification if so:
*/
int handle_futex_death(u32 __user *uaddr, struct task_struct *curr, int pi)
{
u32 uval, nval, mval;
retry:
if (get_user(uval, uaddr))
return -1;
if ((uval & FUTEX_TID_MASK) == task_pid_vnr(curr)) {
/*
* 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;
nval = futex_atomic_cmpxchg_inatomic(uaddr, uval, mval);
if (nval == -EFAULT)
return -1;
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,
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.
*/
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, next_pi, pip;
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))
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);
}
long do_futex(u32 __user *uaddr, int op, u32 val, ktime_t *timeout,
u32 __user *uaddr2, u32 val2, u32 val3)
{
int clockrt, ret = -ENOSYS;
int cmd = op & FUTEX_CMD_MASK;
int fshared = 0;
if (!(op & FUTEX_PRIVATE_FLAG))
fshared = 1;
clockrt = op & FUTEX_CLOCK_REALTIME;
if (clockrt && cmd != FUTEX_WAIT_BITSET && cmd != FUTEX_WAIT_REQUEUE_PI)
return -ENOSYS;
switch (cmd) {
case FUTEX_WAIT:
val3 = FUTEX_BITSET_MATCH_ANY;
case FUTEX_WAIT_BITSET:
ret = futex_wait(uaddr, fshared, val, timeout, val3, clockrt);
break;
case FUTEX_WAKE:
val3 = FUTEX_BITSET_MATCH_ANY;
case FUTEX_WAKE_BITSET:
ret = futex_wake(uaddr, fshared, val, val3);
break;
case FUTEX_REQUEUE:
ret = futex_requeue(uaddr, fshared, uaddr2, val, val2, NULL, 0);
break;
case FUTEX_CMP_REQUEUE:
ret = futex_requeue(uaddr, fshared, uaddr2, val, val2, &val3,
0);
break;
case FUTEX_WAKE_OP:
ret = futex_wake_op(uaddr, fshared, uaddr2, val, val2, val3);
break;
case FUTEX_LOCK_PI:
if (futex_cmpxchg_enabled)
ret = futex_lock_pi(uaddr, fshared, val, timeout, 0);
break;
case FUTEX_UNLOCK_PI:
if (futex_cmpxchg_enabled)
ret = futex_unlock_pi(uaddr, fshared);
break;
case FUTEX_TRYLOCK_PI:
if (futex_cmpxchg_enabled)
ret = futex_lock_pi(uaddr, fshared, 0, timeout, 1);
break;
case FUTEX_WAIT_REQUEUE_PI:
val3 = FUTEX_BITSET_MATCH_ANY;
ret = futex_wait_requeue_pi(uaddr, fshared, val, timeout, val3,
clockrt, uaddr2);
break;
case FUTEX_CMP_REQUEUE_PI:
ret = futex_requeue(uaddr, fshared, uaddr2, val, val2, &val3,
1);
break;
default:
ret = -ENOSYS;
}
return ret;
}
SYSCALL_DEFINE6(futex, u32 __user *, uaddr, int, op, u32, val,
struct timespec __user *, utime, u32 __user *, uaddr2,
u32, val3)
{
struct timespec 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 (copy_from_user(&ts, utime, sizeof(ts)) != 0)
return -EFAULT;
if (!timespec_valid(&ts))
return -EINVAL;
t = timespec_to_ktime(ts);
if (cmd == FUTEX_WAIT)
t = ktime_add_safe(ktime_get(), 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);
}
static int __init futex_init(void)
{
u32 curval;
int i;
/*
* This will fail and we want it. Some arch implementations do
* runtime detection of the futex_atomic_cmpxchg_inatomic()
* functionality. We want to know that before we call in any
* of the complex code paths. Also we want to prevent
* registration of robust lists in that case. NULL is
* guaranteed to fault and we get -EFAULT on functional
* implementation, the non functional ones will return
* -ENOSYS.
*/
curval = cmpxchg_futex_value_locked(NULL, 0, 0);
if (curval == -EFAULT)
futex_cmpxchg_enabled = 1;
for (i = 0; i < ARRAY_SIZE(futex_queues); i++) {
plist_head_init(&futex_queues[i].chain, &futex_queues[i].lock);
spin_lock_init(&futex_queues[i].lock);
}
return 0;
}
__initcall(futex_init);
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