memory-failure.c

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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_MEMCG_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 a signal.
 * ``action optional'' if they are not immediately affected by the error
 * ``action required'' if error happened in current execution context
 */
static int kill_proc(struct task_struct *t, unsigned long addr, int trapno,
            unsigned long pfn, struct page *page, int flags)
{
    struct siginfo si;
    int ret;

    printk(KERN_ERR
        "MCE %#lx: Killing %s:%d due to hardware memory corruption\n",
        pfn, t->comm, t->pid);
    si.si_signo = SIGBUS;
    si.si_errno = 0;
    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;

    if ((flags & MF_ACTION_REQUIRED) && t == current) {
        si.si_code = BUS_MCEERR_AR;
        ret = force_sig_info(SIGBUS, &si, t);
    } else {
        /*
         * 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?
         */
        si.si_code = BUS_MCEERR_AO;
        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(struct list_head *to_kill, int forcekill, int trapno,
              int fail, struct page *page, unsigned long pfn,
              int flags)
{
    struct to_kill *tk, *next;

    list_for_each_entry_safe (tk, next, to_kill, nd) {
        if (forcekill) {
            /*
             * 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(tk->tsk, tk->addr, trapno,
                          pfn, page, flags) < 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;
    pgoff_t pgoff;

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

    pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT);
    read_lock(&tasklist_lock);
    for_each_process (tsk) {
        struct anon_vma_chain *vmac;

        if (!task_early_kill(tsk))
            continue;
        anon_vma_interval_tree_foreach(vmac, &av->rb_root,
                           pgoff, pgoff) {
            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 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_interval_tree_foreach(vma, &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, int flags)
{
    enum ttu_flags ttu = TTU_UNMAP | TTU_IGNORE_MLOCK | TTU_IGNORE_ACCESS;
    struct address_space *mapping;
    LIST_HEAD(tokill);
    int ret;
    int kill = 1, forcekill;
    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 (!(flags & MF_MUST_KILL) && !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 or the process is not restartable,
     * 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.
     */
    forcekill = PageDirty(ppage) || (flags & MF_MUST_KILL);
    kill_procs(&tokill, forcekill, trapno,
              ret != SWAP_SUCCESS, p, pfn, flags);

    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) && !PageTransTail(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, flags) != 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);

#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);

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);

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("%s: %#lx free huge page\n", __func__, pfn);
            ret = dequeue_hwpoisoned_huge_page(compound_head(p));
        } else if (is_free_buddy_page(p)) {
            pr_info("%s: %#lx free buddy page\n", __func__, pfn);
            /* Set hwpoison bit while page is still isolated */
            SetPageHWPoison(p);
            ret = 0;
        } else {
            pr_info("%s: %#lx: unknown zero refcount page type %lx\n",
                __func__, pfn, p->flags);
            ret = -EIO;
        }
    } else {
        /* Not a free page */
        ret = 1;
    }
    unset_migratetype_isolate(p, MIGRATE_MOVABLE);
    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);

    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. */
    ret = migrate_huge_page(hpage, new_page, MPOL_MF_MOVE_ALL, false,
                MIGRATE_SYNC);
    put_page(hpage);
    if (ret) {
        pr_info("soft offline: %#lx: migration failed %d, type %lx\n",
            pfn, ret, page->flags);
        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;
}

int soft_offline_page(struct page *page, int flags)
{
    int ret;
    unsigned long pfn = page_to_pfn(page);
    struct page *hpage = compound_trans_head(page);

    if (PageHuge(page))
        return soft_offline_huge_page(page, flags);
    if (PageTransHuge(hpage)) {
        if (PageAnon(hpage) && unlikely(split_huge_page(hpage))) {
            pr_info("soft offline: %#lx: failed to split THP\n",
                pfn);
            return -EBUSY;
        }
    }

    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;
}