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/*
* Copyright (C) 2008, 2009 Intel Corporation
* Authors: Andi Kleen, Fengguang Wu
*
* This software may be redistributed and/or modified under the terms of
* the GNU General Public License ("GPL") version 2 only as published by the
* Free Software Foundation.
*
* High level machine check handler. Handles pages reported by the
* hardware as being corrupted usually due to a multi-bit ECC memory or cache
* failure.
*
* In addition there is a "soft offline" entry point that allows stop using
* not-yet-corrupted-by-suspicious pages without killing anything.
*
* Handles page cache pages in various states. The tricky part
* here is that we can access any page asynchronously in respect to
* other VM users, because memory failures could happen anytime and
* anywhere. This could violate some of their assumptions. This is why
* this code has to be extremely careful. Generally it tries to use
* normal locking rules, as in get the standard locks, even if that means
* the error handling takes potentially a long time.
*
* There are several operations here with exponential complexity because
* of unsuitable VM data structures. For example the operation to map back
* from RMAP chains to processes has to walk the complete process list and
* has non linear complexity with the number. But since memory corruptions
* are rare we hope to get away with this. This avoids impacting the core
* VM.
*/

/*
* Notebook:
* - hugetlb needs more code
* - kcore/oldmem/vmcore/mem/kmem check for hwpoison pages
* - pass bad pages to kdump next kernel
*/
#include <linux/kernel.h>
#include <linux/mm.h>
#include <linux/page-flags.h>
#include <linux/kernel-page-flags.h>
#include <linux/sched.h>
#include <linux/ksm.h>
#include <linux/rmap.h>
#include <linux/export.h>
#include <linux/pagemap.h>
#include <linux/swap.h>
#include <linux/backing-dev.h>
#include <linux/migrate.h>
#include <linux/page-isolation.h>
#include <linux/suspend.h>
#include <linux/slab.h>
#include <linux/swapops.h>
#include <linux/hugetlb.h>
#include <linux/memory_hotplug.h>
#include <linux/mm_inline.h>
#include <linux/kfifo.h>
#include "internal.h"

int sysctl_memory_failure_early_kill __read_mostly = 0;

int sysctl_memory_failure_recovery __read_mostly = 1;

atomic_long_t mce_bad_pages __read_mostly = ATOMIC_LONG_INIT(0);

#if defined(CONFIG_HWPOISON_INJECT) || defined(CONFIG_HWPOISON_INJECT_MODULE)

u32 hwpoison_filter_enable = 0;
u32 hwpoison_filter_dev_major = ~0U;
u32 hwpoison_filter_dev_minor = ~0U;
u64 hwpoison_filter_flags_mask;
u64 hwpoison_filter_flags_value;
EXPORT_SYMBOL_GPL(hwpoison_filter_enable);
EXPORT_SYMBOL_GPL(hwpoison_filter_dev_major);
EXPORT_SYMBOL_GPL(hwpoison_filter_dev_minor);
EXPORT_SYMBOL_GPL(hwpoison_filter_flags_mask);
EXPORT_SYMBOL_GPL(hwpoison_filter_flags_value);

static int hwpoison_filter_dev(struct page *p)
{
struct address_space *mapping;
dev_t dev;

if (hwpoison_filter_dev_major == ~0U &&
hwpoison_filter_dev_minor == ~0U)
return 0;

/*
* page_mapping() does not accept slab pages.
*/
if (PageSlab(p))
return -EINVAL;

mapping = page_mapping(p);
if (mapping == NULL || mapping->host == NULL)
return -EINVAL;

dev = mapping->host->i_sb->s_dev;
if (hwpoison_filter_dev_major != ~0U &&
hwpoison_filter_dev_major != MAJOR(dev))
return -EINVAL;
if (hwpoison_filter_dev_minor != ~0U &&
hwpoison_filter_dev_minor != MINOR(dev))
return -EINVAL;

return 0;
}

static int hwpoison_filter_flags(struct page *p)
{
if (!hwpoison_filter_flags_mask)
return 0;

if ((stable_page_flags(p) & hwpoison_filter_flags_mask) ==
hwpoison_filter_flags_value)
return 0;
else
return -EINVAL;
}

/*
* This allows stress tests to limit test scope to a collection of tasks
* by putting them under some memcg. This prevents killing unrelated/important
* processes such as /sbin/init. Note that the target task may share clean
* pages with init (eg. libc text), which is harmless. If the target task
* share _dirty_ pages with another task B, the test scheme must make sure B
* is also included in the memcg. At last, due to race conditions this filter
* can only guarantee that the page either belongs to the memcg tasks, or is
* a freed page.
*/
#ifdef CONFIG_CGROUP_MEM_RES_CTLR_SWAP
u64 hwpoison_filter_memcg;
EXPORT_SYMBOL_GPL(hwpoison_filter_memcg);
static int hwpoison_filter_task(struct page *p)
{
struct mem_cgroup *mem;
struct cgroup_subsys_state *css;
unsigned long ino;

if (!hwpoison_filter_memcg)
return 0;

mem = try_get_mem_cgroup_from_page(p);
if (!mem)
return -EINVAL;

css = mem_cgroup_css(mem);
/* root_mem_cgroup has NULL dentries */
if (!css->cgroup->dentry)
return -EINVAL;

ino = css->cgroup->dentry->d_inode->i_ino;
css_put(css);

if (ino != hwpoison_filter_memcg)
return -EINVAL;

return 0;
}
#else
static int hwpoison_filter_task(struct page *p) { return 0; }
#endif

int hwpoison_filter(struct page *p)
{
if (!hwpoison_filter_enable)
return 0;

if (hwpoison_filter_dev(p))
return -EINVAL;

if (hwpoison_filter_flags(p))
return -EINVAL;

if (hwpoison_filter_task(p))
return -EINVAL;

return 0;
}
#else
int hwpoison_filter(struct page *p)
{
return 0;
}
#endif

EXPORT_SYMBOL_GPL(hwpoison_filter);

/*
* Send all the processes who have the page mapped an ``action optional''
* signal.
*/
static int kill_proc_ao(struct task_struct *t, unsigned long addr, int trapno,
unsigned long pfn, struct page *page)
{
struct siginfo si;
int ret;

printk(KERN_ERR
"MCE %#lx: Killing %s:%d early due to hardware memory corruption\n",
pfn, t->comm, t->pid);
si.si_signo = SIGBUS;
si.si_errno = 0;
si.si_code = BUS_MCEERR_AO;
si.si_addr = (void *)addr;
#ifdef __ARCH_SI_TRAPNO
si.si_trapno = trapno;
#endif
si.si_addr_lsb = compound_trans_order(compound_head(page)) + PAGE_SHIFT;
/*
* Don't use force here, it's convenient if the signal
* can be temporarily blocked.
* This could cause a loop when the user sets SIGBUS
* to SIG_IGN, but hopefully no one will do that?
*/
ret = send_sig_info(SIGBUS, &si, t); /* synchronous? */
if (ret < 0)
printk(KERN_INFO "MCE: Error sending signal to %s:%d: %d\n",
t->comm, t->pid, ret);
return ret;
}

/*
* When a unknown page type is encountered drain as many buffers as possible
* in the hope to turn the page into a LRU or free page, which we can handle.
*/
void shake_page(struct page *p, int access)
{
if (!PageSlab(p)) {
lru_add_drain_all();
if (PageLRU(p))
return;
drain_all_pages();
if (PageLRU(p) || is_free_buddy_page(p))
return;
}

/*
* Only call shrink_slab here (which would also shrink other caches) if
* access is not potentially fatal.
*/
if (access) {
int nr;
do {
struct shrink_control shrink = {
.gfp_mask = GFP_KERNEL,
};

nr = shrink_slab(&shrink, 1000, 1000);
if (page_count(p) == 1)
break;
} while (nr > 10);
}
}
EXPORT_SYMBOL_GPL(shake_page);

/*
* Kill all processes that have a poisoned page mapped and then isolate
* the page.
*
* General strategy:
* Find all processes having the page mapped and kill them.
* But we keep a page reference around so that the page is not
* actually freed yet.
* Then stash the page away
*
* There's no convenient way to get back to mapped processes
* from the VMAs. So do a brute-force search over all
* running processes.
*
* Remember that machine checks are not common (or rather
* if they are common you have other problems), so this shouldn't
* be a performance issue.
*
* Also there are some races possible while we get from the
* error detection to actually handle it.
*/

struct to_kill {
struct list_head nd;
struct task_struct *tsk;
unsigned long addr;
char addr_valid;
};

/*
* Failure handling: if we can't find or can't kill a process there's
* not much we can do. We just print a message and ignore otherwise.
*/

/*
* Schedule a process for later kill.
* Uses GFP_ATOMIC allocations to avoid potential recursions in the VM.
* TBD would GFP_NOIO be enough?
*/
static void add_to_kill(struct task_struct *tsk, struct page *p,
struct vm_area_struct *vma,
struct list_head *to_kill,
struct to_kill **tkc)
{
struct to_kill *tk;

if (*tkc) {
tk = *tkc;
*tkc = NULL;
} else {
tk = kmalloc(sizeof(struct to_kill), GFP_ATOMIC);
if (!tk) {
printk(KERN_ERR
"MCE: Out of memory while machine check handling\n");
return;
}
}
tk->addr = page_address_in_vma(p, vma);
tk->addr_valid = 1;

/*
* In theory we don't have to kill when the page was
* munmaped. But it could be also a mremap. Since that's
* likely very rare kill anyways just out of paranoia, but use
* a SIGKILL because the error is not contained anymore.
*/
if (tk->addr == -EFAULT) {
pr_info("MCE: Unable to find user space address %lx in %s\n",
page_to_pfn(p), tsk->comm);
tk->addr_valid = 0;
}
get_task_struct(tsk);
tk->tsk = tsk;
list_add_tail(&tk->nd, to_kill);
}

/*
* Kill the processes that have been collected earlier.
*
* Only do anything when DOIT is set, otherwise just free the list
* (this is used for clean pages which do not need killing)
* Also when FAIL is set do a force kill because something went
* wrong earlier.
*/
static void kill_procs_ao(struct list_head *to_kill, int doit, int trapno,
int fail, struct page *page, unsigned long pfn)
{
struct to_kill *tk, *next;

list_for_each_entry_safe (tk, next, to_kill, nd) {
if (doit) {
/*
* In case something went wrong with munmapping
* make sure the process doesn't catch the
* signal and then access the memory. Just kill it.
*/
if (fail || tk->addr_valid == 0) {
printk(KERN_ERR
"MCE %#lx: forcibly killing %s:%d because of failure to unmap corrupted page\n",
pfn, tk->tsk->comm, tk->tsk->pid);
force_sig(SIGKILL, tk->tsk);
}

/*
* In theory the process could have mapped
* something else on the address in-between. We could
* check for that, but we need to tell the
* process anyways.
*/
else if (kill_proc_ao(tk->tsk, tk->addr, trapno,
pfn, page) < 0)
printk(KERN_ERR
"MCE %#lx: Cannot send advisory machine check signal to %s:%d\n",
pfn, tk->tsk->comm, tk->tsk->pid);
}
put_task_struct(tk->tsk);
kfree(tk);
}
}

static int task_early_kill(struct task_struct *tsk)
{
if (!tsk->mm)
return 0;
if (tsk->flags & PF_MCE_PROCESS)
return !!(tsk->flags & PF_MCE_EARLY);
return sysctl_memory_failure_early_kill;
}

/*
* Collect processes when the error hit an anonymous page.
*/
static void collect_procs_anon(struct page *page, struct list_head *to_kill,
struct to_kill **tkc)
{
struct vm_area_struct *vma;
struct task_struct *tsk;
struct anon_vma *av;

av = page_lock_anon_vma(page);
if (av == NULL) /* Not actually mapped anymore */
return;

read_lock(&tasklist_lock);
for_each_process (tsk) {
struct anon_vma_chain *vmac;

if (!task_early_kill(tsk))
continue;
list_for_each_entry(vmac, &av->head, same_anon_vma) {
vma = vmac->vma;
if (!page_mapped_in_vma(page, vma))
continue;
if (vma->vm_mm == tsk->mm)
add_to_kill(tsk, page, vma, to_kill, tkc);
}
}
read_unlock(&tasklist_lock);
page_unlock_anon_vma(av);
}

/*
* Collect processes when the error hit a file mapped page.
*/
static void collect_procs_file(struct page *page, struct list_head *to_kill,
struct to_kill **tkc)
{
struct vm_area_struct *vma;
struct task_struct *tsk;
struct prio_tree_iter iter;
struct address_space *mapping = page->mapping;

mutex_lock(&mapping->i_mmap_mutex);
read_lock(&tasklist_lock);
for_each_process(tsk) {
pgoff_t pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT);

if (!task_early_kill(tsk))
continue;

vma_prio_tree_foreach(vma, &iter, &mapping->i_mmap, pgoff,
pgoff) {
/*
* Send early kill signal to tasks where a vma covers
* the page but the corrupted page is not necessarily
* mapped it in its pte.
* Assume applications who requested early kill want
* to be informed of all such data corruptions.
*/
if (vma->vm_mm == tsk->mm)
add_to_kill(tsk, page, vma, to_kill, tkc);
}
}
read_unlock(&tasklist_lock);
mutex_unlock(&mapping->i_mmap_mutex);
}

/*
* Collect the processes who have the corrupted page mapped to kill.
* This is done in two steps for locking reasons.
* First preallocate one tokill structure outside the spin locks,
* so that we can kill at least one process reasonably reliable.
*/
static void collect_procs(struct page *page, struct list_head *tokill)
{
struct to_kill *tk;

if (!page->mapping)
return;

tk = kmalloc(sizeof(struct to_kill), GFP_NOIO);
if (!tk)
return;
if (PageAnon(page))
collect_procs_anon(page, tokill, &tk);
else
collect_procs_file(page, tokill, &tk);
kfree(tk);
}

/*
* Error handlers for various types of pages.
*/

enum outcome {
IGNORED, /* Error: cannot be handled */
FAILED, /* Error: handling failed */
DELAYED, /* Will be handled later */
RECOVERED, /* Successfully recovered */
};

static const char *action_name[] = {
[IGNORED] = "Ignored",
[FAILED] = "Failed",
[DELAYED] = "Delayed",
[RECOVERED] = "Recovered",
};

/*
* XXX: It is possible that a page is isolated from LRU cache,
* and then kept in swap cache or failed to remove from page cache.
* The page count will stop it from being freed by unpoison.
* Stress tests should be aware of this memory leak problem.
*/
static int delete_from_lru_cache(struct page *p)
{
if (!isolate_lru_page(p)) {
/*
* Clear sensible page flags, so that the buddy system won't
* complain when the page is unpoison-and-freed.
*/
ClearPageActive(p);
ClearPageUnevictable(p);
/*
* drop the page count elevated by isolate_lru_page()
*/
page_cache_release(p);
return 0;
}
return -EIO;
}

/*
* Error hit kernel page.
* Do nothing, try to be lucky and not touch this instead. For a few cases we
* could be more sophisticated.
*/
static int me_kernel(struct page *p, unsigned long pfn)
{
return IGNORED;
}

/*
* Page in unknown state. Do nothing.
*/
static int me_unknown(struct page *p, unsigned long pfn)
{
printk(KERN_ERR "MCE %#lx: Unknown page state\n", pfn);
return FAILED;
}

/*
* Clean (or cleaned) page cache page.
*/
static int me_pagecache_clean(struct page *p, unsigned long pfn)
{
int err;
int ret = FAILED;
struct address_space *mapping;

delete_from_lru_cache(p);

/*
* For anonymous pages we're done the only reference left
* should be the one m_f() holds.
*/
if (PageAnon(p))
return RECOVERED;

/*
* Now truncate the page in the page cache. This is really
* more like a "temporary hole punch"
* Don't do this for block devices when someone else
* has a reference, because it could be file system metadata
* and that's not safe to truncate.
*/
mapping = page_mapping(p);
if (!mapping) {
/*
* Page has been teared down in the meanwhile
*/
return FAILED;
}

/*
* Truncation is a bit tricky. Enable it per file system for now.
*
* Open: to take i_mutex or not for this? Right now we don't.
*/
if (mapping->a_ops->error_remove_page) {
err = mapping->a_ops->error_remove_page(mapping, p);
if (err != 0) {
printk(KERN_INFO "MCE %#lx: Failed to punch page: %d\n",
pfn, err);
} else if (page_has_private(p) &&
!try_to_release_page(p, GFP_NOIO)) {
pr_info("MCE %#lx: failed to release buffers\n", pfn);
} else {
ret = RECOVERED;
}
} else {
/*
* If the file system doesn't support it just invalidate
* This fails on dirty or anything with private pages
*/
if (invalidate_inode_page(p))
ret = RECOVERED;
else
printk(KERN_INFO "MCE %#lx: Failed to invalidate\n",
pfn);
}
return ret;
}

/*
* Dirty cache page page
* Issues: when the error hit a hole page the error is not properly
* propagated.
*/
static int me_pagecache_dirty(struct page *p, unsigned long pfn)
{
struct address_space *mapping = page_mapping(p);

SetPageError(p);
/* TBD: print more information about the file. */
if (mapping) {
/*
* IO error will be reported by write(), fsync(), etc.
* who check the mapping.
* This way the application knows that something went
* wrong with its dirty file data.
*
* There's one open issue:
*
* The EIO will be only reported on the next IO
* operation and then cleared through the IO map.
* Normally Linux has two mechanisms to pass IO error
* first through the AS_EIO flag in the address space
* and then through the PageError flag in the page.
* Since we drop pages on memory failure handling the
* only mechanism open to use is through AS_AIO.
*
* This has the disadvantage that it gets cleared on
* the first operation that returns an error, while
* the PageError bit is more sticky and only cleared
* when the page is reread or dropped. If an
* application assumes it will always get error on
* fsync, but does other operations on the fd before
* and the page is dropped between then the error
* will not be properly reported.
*
* This can already happen even without hwpoisoned
* pages: first on metadata IO errors (which only
* report through AS_EIO) or when the page is dropped
* at the wrong time.
*
* So right now we assume that the application DTRT on
* the first EIO, but we're not worse than other parts
* of the kernel.
*/
mapping_set_error(mapping, EIO);
}

return me_pagecache_clean(p, pfn);
}

/*
* Clean and dirty swap cache.
*
* Dirty swap cache page is tricky to handle. The page could live both in page
* cache and swap cache(ie. page is freshly swapped in). So it could be
* referenced concurrently by 2 types of PTEs:
* normal PTEs and swap PTEs. We try to handle them consistently by calling
* try_to_unmap(TTU_IGNORE_HWPOISON) to convert the normal PTEs to swap PTEs,
* and then
* - clear dirty bit to prevent IO
* - remove from LRU
* - but keep in the swap cache, so that when we return to it on
* a later page fault, we know the application is accessing
* corrupted data and shall be killed (we installed simple
* interception code in do_swap_page to catch it).
*
* Clean swap cache pages can be directly isolated. A later page fault will
* bring in the known good data from disk.
*/
static int me_swapcache_dirty(struct page *p, unsigned long pfn)
{
ClearPageDirty(p);
/* Trigger EIO in shmem: */
ClearPageUptodate(p);

if (!delete_from_lru_cache(p))
return DELAYED;
else
return FAILED;
}

static int me_swapcache_clean(struct page *p, unsigned long pfn)
{
delete_from_swap_cache(p);

if (!delete_from_lru_cache(p))
return RECOVERED;
else
return FAILED;
}

/*
* Huge pages. Needs work.
* Issues:
* - Error on hugepage is contained in hugepage unit (not in raw page unit.)
* To narrow down kill region to one page, we need to break up pmd.
*/
static int me_huge_page(struct page *p, unsigned long pfn)
{
int res = 0;
struct page *hpage = compound_head(p);
/*
* We can safely recover from error on free or reserved (i.e.
* not in-use) hugepage by dequeuing it from freelist.
* To check whether a hugepage is in-use or not, we can't use
* page->lru because it can be used in other hugepage operations,
* such as __unmap_hugepage_range() and gather_surplus_pages().
* So instead we use page_mapping() and PageAnon().
* We assume that this function is called with page lock held,
* so there is no race between isolation and mapping/unmapping.
*/
if (!(page_mapping(hpage) || PageAnon(hpage))) {
res = dequeue_hwpoisoned_huge_page(hpage);
if (!res)
return RECOVERED;
}
return DELAYED;
}

/*
* Various page states we can handle.
*
* A page state is defined by its current page->flags bits.
* The table matches them in order and calls the right handler.
*
* This is quite tricky because we can access page at any time
* in its live cycle, so all accesses have to be extremely careful.
*
* This is not complete. More states could be added.
* For any missing state don't attempt recovery.
*/

#define dirty (1UL << PG_dirty)
#define sc (1UL << PG_swapcache)
#define unevict (1UL << PG_unevictable)
#define mlock (1UL << PG_mlocked)
#define writeback (1UL << PG_writeback)
#define lru (1UL << PG_lru)
#define swapbacked (1UL << PG_swapbacked)
#define head (1UL << PG_head)
#define tail (1UL << PG_tail)
#define compound (1UL << PG_compound)
#define slab (1UL << PG_slab)
#define reserved (1UL << PG_reserved)

static struct page_state {
unsigned long mask;
unsigned long res;
char *msg;
int (*action)(struct page *p, unsigned long pfn);
} error_states[] = {
{ reserved, reserved, "reserved kernel", me_kernel },
/*
* free pages are specially detected outside this table:
* PG_buddy pages only make a small fraction of all free pages.
*/

/*
* Could in theory check if slab page is free or if we can drop
* currently unused objects without touching them. But just
* treat it as standard kernel for now.
*/
{ slab, slab, "kernel slab", me_kernel },

#ifdef CONFIG_PAGEFLAGS_EXTENDED
{ head, head, "huge", me_huge_page },
{ tail, tail, "huge", me_huge_page },
#else
{ compound, compound, "huge", me_huge_page },
#endif

{ sc|dirty, sc|dirty, "swapcache", me_swapcache_dirty },
{ sc|dirty, sc, "swapcache", me_swapcache_clean },

{ unevict|dirty, unevict|dirty, "unevictable LRU", me_pagecache_dirty},
{ unevict, unevict, "unevictable LRU", me_pagecache_clean},

{ mlock|dirty, mlock|dirty, "mlocked LRU", me_pagecache_dirty },
{ mlock, mlock, "mlocked LRU", me_pagecache_clean },

{ lru|dirty, lru|dirty, "LRU", me_pagecache_dirty },
{ lru|dirty, lru, "clean LRU", me_pagecache_clean },

/*
* Catchall entry: must be at end.
*/
{ 0, 0, "unknown page state", me_unknown },
};

#undef dirty
#undef sc
#undef unevict
#undef mlock
#undef writeback
#undef lru
#undef swapbacked
#undef head
#undef tail
#undef compound
#undef slab
#undef reserved

static void action_result(unsigned long pfn, char *msg, int result)
{
struct page *page = pfn_to_page(pfn);

printk(KERN_ERR "MCE %#lx: %s%s page recovery: %s\n",
pfn,
PageDirty(page) ? "dirty " : "",
msg, action_name[result]);
}

static int page_action(struct page_state *ps, struct page *p,
unsigned long pfn)
{
int result;
int count;

result = ps->action(p, pfn);
action_result(pfn, ps->msg, result);

count = page_count(p) - 1;
if (ps->action == me_swapcache_dirty && result == DELAYED)
count--;
if (count != 0) {
printk(KERN_ERR
"MCE %#lx: %s page still referenced by %d users\n",
pfn, ps->msg, count);
result = FAILED;
}

/* Could do more checks here if page looks ok */
/*
* Could adjust zone counters here to correct for the missing page.
*/

return (result == RECOVERED || result == DELAYED) ? 0 : -EBUSY;
}

/*
* Do all that is necessary to remove user space mappings. Unmap
* the pages and send SIGBUS to the processes if the data was dirty.
*/
static int hwpoison_user_mappings(struct page *p, unsigned long pfn,
int trapno)
{
enum ttu_flags ttu = TTU_UNMAP | TTU_IGNORE_MLOCK | TTU_IGNORE_ACCESS;
struct address_space *mapping;
LIST_HEAD(tokill);
int ret;
int kill = 1;
struct page *hpage = compound_head(p);
struct page *ppage;

if (PageReserved(p) || PageSlab(p))
return SWAP_SUCCESS;

/*
* This check implies we don't kill processes if their pages
* are in the swap cache early. Those are always late kills.
*/
if (!page_mapped(hpage))
return SWAP_SUCCESS;

if (PageKsm(p))
return SWAP_FAIL;

if (PageSwapCache(p)) {
printk(KERN_ERR
"MCE %#lx: keeping poisoned page in swap cache\n", pfn);
ttu |= TTU_IGNORE_HWPOISON;
}

/*
* Propagate the dirty bit from PTEs to struct page first, because we
* need this to decide if we should kill or just drop the page.
* XXX: the dirty test could be racy: set_page_dirty() may not always
* be called inside page lock (it's recommended but not enforced).
*/
mapping = page_mapping(hpage);
if (!PageDirty(hpage) && mapping &&
mapping_cap_writeback_dirty(mapping)) {
if (page_mkclean(hpage)) {
SetPageDirty(hpage);
} else {
kill = 0;
ttu |= TTU_IGNORE_HWPOISON;
printk(KERN_INFO
"MCE %#lx: corrupted page was clean: dropped without side effects\n",
pfn);
}
}

/*
* ppage: poisoned page
* if p is regular page(4k page)
* ppage == real poisoned page;
* else p is hugetlb or THP, ppage == head page.
*/
ppage = hpage;

if (PageTransHuge(hpage)) {
/*
* Verify that this isn't a hugetlbfs head page, the check for
* PageAnon is just for avoid tripping a split_huge_page
* internal debug check, as split_huge_page refuses to deal with
* anything that isn't an anon page. PageAnon can't go away fro
* under us because we hold a refcount on the hpage, without a
* refcount on the hpage. split_huge_page can't be safely called
* in the first place, having a refcount on the tail isn't
* enough * to be safe.
*/
if (!PageHuge(hpage) && PageAnon(hpage)) {
if (unlikely(split_huge_page(hpage))) {
/*
* FIXME: if splitting THP is failed, it is
* better to stop the following operation rather
* than causing panic by unmapping. System might
* survive if the page is freed later.
*/
printk(KERN_INFO
"MCE %#lx: failed to split THP\n", pfn);

BUG_ON(!PageHWPoison(p));
return SWAP_FAIL;
}
/* THP is split, so ppage should be the real poisoned page. */
ppage = p;
}
}

/*
* First collect all the processes that have the page
* mapped in dirty form. This has to be done before try_to_unmap,
* because ttu takes the rmap data structures down.
*
* Error handling: We ignore errors here because
* there's nothing that can be done.
*/
if (kill)
collect_procs(ppage, &tokill);

if (hpage != ppage)
lock_page(ppage);

ret = try_to_unmap(ppage, ttu);
if (ret != SWAP_SUCCESS)
printk(KERN_ERR "MCE %#lx: failed to unmap page (mapcount=%d)\n",
pfn, page_mapcount(ppage));

if (hpage != ppage)
unlock_page(ppage);

/*
* Now that the dirty bit has been propagated to the
* struct page and all unmaps done we can decide if
* killing is needed or not. Only kill when the page
* was dirty, otherwise the tokill list is merely
* freed. When there was a problem unmapping earlier
* use a more force-full uncatchable kill to prevent
* any accesses to the poisoned memory.
*/
kill_procs_ao(&tokill, !!PageDirty(ppage), trapno,
ret != SWAP_SUCCESS, p, pfn);

return ret;
}

static void set_page_hwpoison_huge_page(struct page *hpage)
{
int i;
int nr_pages = 1 << compound_trans_order(hpage);
for (i = 0; i < nr_pages; i++)
SetPageHWPoison(hpage + i);
}

static void clear_page_hwpoison_huge_page(struct page *hpage)
{
int i;
int nr_pages = 1 << compound_trans_order(hpage);
for (i = 0; i < nr_pages; i++)
ClearPageHWPoison(hpage + i);
}

int __memory_failure(unsigned long pfn, int trapno, int flags)
{
struct page_state *ps;
struct page *p;
struct page *hpage;
int res;
unsigned int nr_pages;

if (!sysctl_memory_failure_recovery)
panic("Memory failure from trap %d on page %lx", trapno, pfn);

if (!pfn_valid(pfn)) {
printk(KERN_ERR
"MCE %#lx: memory outside kernel control\n",
pfn);
return -ENXIO;
}

p = pfn_to_page(pfn);
hpage = compound_head(p);
if (TestSetPageHWPoison(p)) {
printk(KERN_ERR "MCE %#lx: already hardware poisoned\n", pfn);
return 0;
}

nr_pages = 1 << compound_trans_order(hpage);
atomic_long_add(nr_pages, &mce_bad_pages);

/*
* We need/can do nothing about count=0 pages.
* 1) it's a free page, and therefore in safe hand:
* prep_new_page() will be the gate keeper.
* 2) it's a free hugepage, which is also safe:
* an affected hugepage will be dequeued from hugepage freelist,
* so there's no concern about reusing it ever after.
* 3) it's part of a non-compound high order page.
* Implies some kernel user: cannot stop them from
* R/W the page; let's pray that the page has been
* used and will be freed some time later.
* In fact it's dangerous to directly bump up page count from 0,
* that may make page_freeze_refs()/page_unfreeze_refs() mismatch.
*/
if (!(flags & MF_COUNT_INCREASED) &&
!get_page_unless_zero(hpage)) {
if (is_free_buddy_page(p)) {
action_result(pfn, "free buddy", DELAYED);
return 0;
} else if (PageHuge(hpage)) {
/*
* Check "just unpoisoned", "filter hit", and
* "race with other subpage."
*/
lock_page(hpage);
if (!PageHWPoison(hpage)
|| (hwpoison_filter(p) && TestClearPageHWPoison(p))
|| (p != hpage && TestSetPageHWPoison(hpage))) {
atomic_long_sub(nr_pages, &mce_bad_pages);
return 0;
}
set_page_hwpoison_huge_page(hpage);
res = dequeue_hwpoisoned_huge_page(hpage);
action_result(pfn, "free huge",
res ? IGNORED : DELAYED);
unlock_page(hpage);
return res;
} else {
action_result(pfn, "high order kernel", IGNORED);
return -EBUSY;
}
}

/*
* We ignore non-LRU pages for good reasons.
* - PG_locked is only well defined for LRU pages and a few others
* - to avoid races with __set_page_locked()
* - to avoid races with __SetPageSlab*() (and more non-atomic ops)
* The check (unnecessarily) ignores LRU pages being isolated and
* walked by the page reclaim code, however that's not a big loss.
*/
if (!PageHuge(p) && !PageTransCompound(p)) {
if (!PageLRU(p))
shake_page(p, 0);
if (!PageLRU(p)) {
/*
* shake_page could have turned it free.
*/
if (is_free_buddy_page(p)) {
action_result(pfn, "free buddy, 2nd try",
DELAYED);
return 0;
}
action_result(pfn, "non LRU", IGNORED);
put_page(p);
return -EBUSY;
}
}

/*
* Lock the page and wait for writeback to finish.
* It's very difficult to mess with pages currently under IO
* and in many cases impossible, so we just avoid it here.
*/
lock_page(hpage);

/*
* unpoison always clear PG_hwpoison inside page lock
*/
if (!PageHWPoison(p)) {
printk(KERN_ERR "MCE %#lx: just unpoisoned\n", pfn);
res = 0;
goto out;
}
if (hwpoison_filter(p)) {
if (TestClearPageHWPoison(p))
atomic_long_sub(nr_pages, &mce_bad_pages);
unlock_page(hpage);
put_page(hpage);
return 0;
}

/*
* For error on the tail page, we should set PG_hwpoison
* on the head page to show that the hugepage is hwpoisoned
*/
if (PageHuge(p) && PageTail(p) && TestSetPageHWPoison(hpage)) {
action_result(pfn, "hugepage already hardware poisoned",
IGNORED);
unlock_page(hpage);
put_page(hpage);
return 0;
}
/*
* Set PG_hwpoison on all pages in an error hugepage,
* because containment is done in hugepage unit for now.
* Since we have done TestSetPageHWPoison() for the head page with
* page lock held, we can safely set PG_hwpoison bits on tail pages.
*/
if (PageHuge(p))
set_page_hwpoison_huge_page(hpage);

wait_on_page_writeback(p);

/*
* Now take care of user space mappings.
* Abort on fail: __delete_from_page_cache() assumes unmapped page.
*/
if (hwpoison_user_mappings(p, pfn, trapno) != SWAP_SUCCESS) {
printk(KERN_ERR "MCE %#lx: cannot unmap page, give up\n", pfn);
res = -EBUSY;
goto out;
}

/*
* Torn down by someone else?
*/
if (PageLRU(p) && !PageSwapCache(p) && p->mapping == NULL) {
action_result(pfn, "already truncated LRU", IGNORED);
res = -EBUSY;
goto out;
}

res = -EBUSY;
for (ps = error_states;; ps++) {
if ((p->flags & ps->mask) == ps->res) {
res = page_action(ps, p, pfn);
break;
}
}
out:
unlock_page(hpage);
return res;
}
EXPORT_SYMBOL_GPL(__memory_failure);

/**
* memory_failure - Handle memory failure of a page.
* @pfn: Page Number of the corrupted page
* @trapno: Trap number reported in the signal to user space.
*
* This function is called by the low level machine check code
* of an architecture when it detects hardware memory corruption
* of a page. It tries its best to recover, which includes
* dropping pages, killing processes etc.
*
* The function is primarily of use for corruptions that
* happen outside the current execution context (e.g. when
* detected by a background scrubber)
*
* Must run in process context (e.g. a work queue) with interrupts
* enabled and no spinlocks hold.
*/
void memory_failure(unsigned long pfn, int trapno)
{
__memory_failure(pfn, trapno, 0);
}

#define MEMORY_FAILURE_FIFO_ORDER 4
#define MEMORY_FAILURE_FIFO_SIZE (1 << MEMORY_FAILURE_FIFO_ORDER)

struct memory_failure_entry {
unsigned long pfn;
int trapno;
int flags;
};

struct memory_failure_cpu {
DECLARE_KFIFO(fifo, struct memory_failure_entry,
MEMORY_FAILURE_FIFO_SIZE);
spinlock_t lock;
struct work_struct work;
};

static DEFINE_PER_CPU(struct memory_failure_cpu, memory_failure_cpu);

/**
* memory_failure_queue - Schedule handling memory failure of a page.
* @pfn: Page Number of the corrupted page
* @trapno: Trap number reported in the signal to user space.
* @flags: Flags for memory failure handling
*
* This function is called by the low level hardware error handler
* when it detects hardware memory corruption of a page. It schedules
* the recovering of error page, including dropping pages, killing
* processes etc.
*
* The function is primarily of use for corruptions that
* happen outside the current execution context (e.g. when
* detected by a background scrubber)
*
* Can run in IRQ context.
*/
void memory_failure_queue(unsigned long pfn, int trapno, int flags)
{
struct memory_failure_cpu *mf_cpu;
unsigned long proc_flags;
struct memory_failure_entry entry = {
.pfn = pfn,
.trapno = trapno,
.flags = flags,
};

mf_cpu = &get_cpu_var(memory_failure_cpu);
spin_lock_irqsave(&mf_cpu->lock, proc_flags);
if (kfifo_put(&mf_cpu->fifo, &entry))
schedule_work_on(smp_processor_id(), &mf_cpu->work);
else
pr_err("Memory failure: buffer overflow when queuing memory failure at 0x%#lx\n",
pfn);
spin_unlock_irqrestore(&mf_cpu->lock, proc_flags);
put_cpu_var(memory_failure_cpu);
}
EXPORT_SYMBOL_GPL(memory_failure_queue);

static void memory_failure_work_func(struct work_struct *work)
{
struct memory_failure_cpu *mf_cpu;
struct memory_failure_entry entry = { 0, };
unsigned long proc_flags;
int gotten;

mf_cpu = &__get_cpu_var(memory_failure_cpu);
for (;;) {
spin_lock_irqsave(&mf_cpu->lock, proc_flags);
gotten = kfifo_get(&mf_cpu->fifo, &entry);
spin_unlock_irqrestore(&mf_cpu->lock, proc_flags);
if (!gotten)
break;
__memory_failure(entry.pfn, entry.trapno, entry.flags);
}
}

static int __init memory_failure_init(void)
{
struct memory_failure_cpu *mf_cpu;
int cpu;

for_each_possible_cpu(cpu) {
mf_cpu = &per_cpu(memory_failure_cpu, cpu);
spin_lock_init(&mf_cpu->lock);
INIT_KFIFO(mf_cpu->fifo);
INIT_WORK(&mf_cpu->work, memory_failure_work_func);
}

return 0;
}
core_initcall(memory_failure_init);

/**
* unpoison_memory - Unpoison a previously poisoned page
* @pfn: Page number of the to be unpoisoned page
*
* Software-unpoison a page that has been poisoned by
* memory_failure() earlier.
*
* This is only done on the software-level, so it only works
* for linux injected failures, not real hardware failures
*
* Returns 0 for success, otherwise -errno.
*/
int unpoison_memory(unsigned long pfn)
{
struct page *page;
struct page *p;
int freeit = 0;
unsigned int nr_pages;

if (!pfn_valid(pfn))
return -ENXIO;

p = pfn_to_page(pfn);
page = compound_head(p);

if (!PageHWPoison(p)) {
pr_info("MCE: Page was already unpoisoned %#lx\n", pfn);
return 0;
}

nr_pages = 1 << compound_trans_order(page);

if (!get_page_unless_zero(page)) {
/*
* Since HWPoisoned hugepage should have non-zero refcount,
* race between memory failure and unpoison seems to happen.
* In such case unpoison fails and memory failure runs
* to the end.
*/
if (PageHuge(page)) {
pr_info("MCE: Memory failure is now running on free hugepage %#lx\n", pfn);
return 0;
}
if (TestClearPageHWPoison(p))
atomic_long_sub(nr_pages, &mce_bad_pages);
pr_info("MCE: Software-unpoisoned free page %#lx\n", pfn);
return 0;
}

lock_page(page);
/*
* This test is racy because PG_hwpoison is set outside of page lock.
* That's acceptable because that won't trigger kernel panic. Instead,
* the PG_hwpoison page will be caught and isolated on the entrance to
* the free buddy page pool.
*/
if (TestClearPageHWPoison(page)) {
pr_info("MCE: Software-unpoisoned page %#lx\n", pfn);
atomic_long_sub(nr_pages, &mce_bad_pages);
freeit = 1;
if (PageHuge(page))
clear_page_hwpoison_huge_page(page);
}
unlock_page(page);

put_page(page);
if (freeit)
put_page(page);

return 0;
}
EXPORT_SYMBOL(unpoison_memory);

static struct page *new_page(struct page *p, unsigned long private, int **x)
{
int nid = page_to_nid(p);
if (PageHuge(p))
return alloc_huge_page_node(page_hstate(compound_head(p)),
nid);
else
return alloc_pages_exact_node(nid, GFP_HIGHUSER_MOVABLE, 0);
}

/*
* Safely get reference count of an arbitrary page.
* Returns 0 for a free page, -EIO for a zero refcount page
* that is not free, and 1 for any other page type.
* For 1 the page is returned with increased page count, otherwise not.
*/
static int get_any_page(struct page *p, unsigned long pfn, int flags)
{
int ret;

if (flags & MF_COUNT_INCREASED)
return 1;

/*
* The lock_memory_hotplug prevents a race with memory hotplug.
* This is a big hammer, a better would be nicer.
*/
lock_memory_hotplug();

/*
* Isolate the page, so that it doesn't get reallocated if it
* was free.
*/
set_migratetype_isolate(p);
/*
* When the target page is a free hugepage, just remove it
* from free hugepage list.
*/
if (!get_page_unless_zero(compound_head(p))) {
if (PageHuge(p)) {
pr_info("get_any_page: %#lx free huge page\n", pfn);
ret = dequeue_hwpoisoned_huge_page(compound_head(p));
} else if (is_free_buddy_page(p)) {
pr_info("get_any_page: %#lx free buddy page\n", pfn);
/* Set hwpoison bit while page is still isolated */
SetPageHWPoison(p);
ret = 0;
} else {
pr_info("get_any_page: %#lx: unknown zero refcount page type %lx\n",
pfn, p->flags);
ret = -EIO;
}
} else {
/* Not a free page */
ret = 1;
}
unset_migratetype_isolate(p);
unlock_memory_hotplug();
return ret;
}

static int soft_offline_huge_page(struct page *page, int flags)
{
int ret;
unsigned long pfn = page_to_pfn(page);
struct page *hpage = compound_head(page);
LIST_HEAD(pagelist);

ret = get_any_page(page, pfn, flags);
if (ret < 0)
return ret;
if (ret == 0)
goto done;

if (PageHWPoison(hpage)) {
put_page(hpage);
pr_info("soft offline: %#lx hugepage already poisoned\n", pfn);
return -EBUSY;
}

/* Keep page count to indicate a given hugepage is isolated. */

list_add(&hpage->lru, &pagelist);
ret = migrate_huge_pages(&pagelist, new_page, MPOL_MF_MOVE_ALL, false,
MIGRATE_SYNC);
if (ret) {
struct page *page1, *page2;
list_for_each_entry_safe(page1, page2, &pagelist, lru)
put_page(page1);

pr_info("soft offline: %#lx: migration failed %d, type %lx\n",
pfn, ret, page->flags);
if (ret > 0)
ret = -EIO;
return ret;
}
done:
if (!PageHWPoison(hpage))
atomic_long_add(1 << compound_trans_order(hpage), &mce_bad_pages);
set_page_hwpoison_huge_page(hpage);
dequeue_hwpoisoned_huge_page(hpage);
/* keep elevated page count for bad page */
return ret;
}

/**
* soft_offline_page - Soft offline a page.
* @page: page to offline
* @flags: flags. Same as memory_failure().
*
* Returns 0 on success, otherwise negated errno.
*
* Soft offline a page, by migration or invalidation,
* without killing anything. This is for the case when
* a page is not corrupted yet (so it's still valid to access),
* but has had a number of corrected errors and is better taken
* out.
*
* The actual policy on when to do that is maintained by
* user space.
*
* This should never impact any application or cause data loss,
* however it might take some time.
*
* This is not a 100% solution for all memory, but tries to be
* ``good enough'' for the majority of memory.
*/
int soft_offline_page(struct page *page, int flags)
{
int ret;
unsigned long pfn = page_to_pfn(page);

if (PageHuge(page))
return soft_offline_huge_page(page, flags);

ret = get_any_page(page, pfn, flags);
if (ret < 0)
return ret;
if (ret == 0)
goto done;

/*
* Page cache page we can handle?
*/
if (!PageLRU(page)) {
/*
* Try to free it.
*/
put_page(page);
shake_page(page, 1);

/*
* Did it turn free?
*/
ret = get_any_page(page, pfn, 0);
if (ret < 0)
return ret;
if (ret == 0)
goto done;
}
if (!PageLRU(page)) {
pr_info("soft_offline: %#lx: unknown non LRU page type %lx\n",
pfn, page->flags);
return -EIO;
}

lock_page(page);
wait_on_page_writeback(page);

/*
* Synchronized using the page lock with memory_failure()
*/
if (PageHWPoison(page)) {
unlock_page(page);
put_page(page);
pr_info("soft offline: %#lx page already poisoned\n", pfn);
return -EBUSY;
}

/*
* Try to invalidate first. This should work for
* non dirty unmapped page cache pages.
*/
ret = invalidate_inode_page(page);
unlock_page(page);
/*
* RED-PEN would be better to keep it isolated here, but we
* would need to fix isolation locking first.
*/
if (ret == 1) {
put_page(page);
ret = 0;
pr_info("soft_offline: %#lx: invalidated\n", pfn);
goto done;
}

/*
* Simple invalidation didn't work.
* Try to migrate to a new page instead. migrate.c
* handles a large number of cases for us.
*/
ret = isolate_lru_page(page);
/*
* Drop page reference which is came from get_any_page()
* successful isolate_lru_page() already took another one.
*/
put_page(page);
if (!ret) {
LIST_HEAD(pagelist);
inc_zone_page_state(page, NR_ISOLATED_ANON +
page_is_file_cache(page));
list_add(&page->lru, &pagelist);
ret = migrate_pages(&pagelist, new_page, MPOL_MF_MOVE_ALL,
false, MIGRATE_SYNC);
if (ret) {
putback_lru_pages(&pagelist);
pr_info("soft offline: %#lx: migration failed %d, type %lx\n",
pfn, ret, page->flags);
if (ret > 0)
ret = -EIO;
}
} else {
pr_info("soft offline: %#lx: isolation failed: %d, page count %d, type %lx\n",
pfn, ret, page_count(page), page->flags);
}
if (ret)
return ret;

done:
atomic_long_add(1, &mce_bad_pages);
SetPageHWPoison(page);
/* keep elevated page count for bad page */
return ret;
}
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