Root/mm/memory-failure.c

1/*
2 * Copyright (C) 2008, 2009 Intel Corporation
3 * Authors: Andi Kleen, Fengguang Wu
4 *
5 * This software may be redistributed and/or modified under the terms of
6 * the GNU General Public License ("GPL") version 2 only as published by the
7 * Free Software Foundation.
8 *
9 * High level machine check handler. Handles pages reported by the
10 * hardware as being corrupted usually due to a multi-bit ECC memory or cache
11 * failure.
12 *
13 * In addition there is a "soft offline" entry point that allows stop using
14 * not-yet-corrupted-by-suspicious pages without killing anything.
15 *
16 * Handles page cache pages in various states. The tricky part
17 * here is that we can access any page asynchronously in respect to
18 * other VM users, because memory failures could happen anytime and
19 * anywhere. This could violate some of their assumptions. This is why
20 * this code has to be extremely careful. Generally it tries to use
21 * normal locking rules, as in get the standard locks, even if that means
22 * the error handling takes potentially a long time.
23 *
24 * There are several operations here with exponential complexity because
25 * of unsuitable VM data structures. For example the operation to map back
26 * from RMAP chains to processes has to walk the complete process list and
27 * has non linear complexity with the number. But since memory corruptions
28 * are rare we hope to get away with this. This avoids impacting the core
29 * VM.
30 */
31
32/*
33 * Notebook:
34 * - hugetlb needs more code
35 * - kcore/oldmem/vmcore/mem/kmem check for hwpoison pages
36 * - pass bad pages to kdump next kernel
37 */
38#include <linux/kernel.h>
39#include <linux/mm.h>
40#include <linux/page-flags.h>
41#include <linux/kernel-page-flags.h>
42#include <linux/sched.h>
43#include <linux/ksm.h>
44#include <linux/rmap.h>
45#include <linux/pagemap.h>
46#include <linux/swap.h>
47#include <linux/backing-dev.h>
48#include <linux/migrate.h>
49#include <linux/page-isolation.h>
50#include <linux/suspend.h>
51#include <linux/slab.h>
52#include <linux/swapops.h>
53#include <linux/hugetlb.h>
54#include <linux/memory_hotplug.h>
55#include <linux/mm_inline.h>
56#include "internal.h"
57
58int sysctl_memory_failure_early_kill __read_mostly = 0;
59
60int sysctl_memory_failure_recovery __read_mostly = 1;
61
62atomic_long_t mce_bad_pages __read_mostly = ATOMIC_LONG_INIT(0);
63
64#if defined(CONFIG_HWPOISON_INJECT) || defined(CONFIG_HWPOISON_INJECT_MODULE)
65
66u32 hwpoison_filter_enable = 0;
67u32 hwpoison_filter_dev_major = ~0U;
68u32 hwpoison_filter_dev_minor = ~0U;
69u64 hwpoison_filter_flags_mask;
70u64 hwpoison_filter_flags_value;
71EXPORT_SYMBOL_GPL(hwpoison_filter_enable);
72EXPORT_SYMBOL_GPL(hwpoison_filter_dev_major);
73EXPORT_SYMBOL_GPL(hwpoison_filter_dev_minor);
74EXPORT_SYMBOL_GPL(hwpoison_filter_flags_mask);
75EXPORT_SYMBOL_GPL(hwpoison_filter_flags_value);
76
77static int hwpoison_filter_dev(struct page *p)
78{
79    struct address_space *mapping;
80    dev_t dev;
81
82    if (hwpoison_filter_dev_major == ~0U &&
83        hwpoison_filter_dev_minor == ~0U)
84        return 0;
85
86    /*
87     * page_mapping() does not accept slab pages.
88     */
89    if (PageSlab(p))
90        return -EINVAL;
91
92    mapping = page_mapping(p);
93    if (mapping == NULL || mapping->host == NULL)
94        return -EINVAL;
95
96    dev = mapping->host->i_sb->s_dev;
97    if (hwpoison_filter_dev_major != ~0U &&
98        hwpoison_filter_dev_major != MAJOR(dev))
99        return -EINVAL;
100    if (hwpoison_filter_dev_minor != ~0U &&
101        hwpoison_filter_dev_minor != MINOR(dev))
102        return -EINVAL;
103
104    return 0;
105}
106
107static int hwpoison_filter_flags(struct page *p)
108{
109    if (!hwpoison_filter_flags_mask)
110        return 0;
111
112    if ((stable_page_flags(p) & hwpoison_filter_flags_mask) ==
113                    hwpoison_filter_flags_value)
114        return 0;
115    else
116        return -EINVAL;
117}
118
119/*
120 * This allows stress tests to limit test scope to a collection of tasks
121 * by putting them under some memcg. This prevents killing unrelated/important
122 * processes such as /sbin/init. Note that the target task may share clean
123 * pages with init (eg. libc text), which is harmless. If the target task
124 * share _dirty_ pages with another task B, the test scheme must make sure B
125 * is also included in the memcg. At last, due to race conditions this filter
126 * can only guarantee that the page either belongs to the memcg tasks, or is
127 * a freed page.
128 */
129#ifdef CONFIG_CGROUP_MEM_RES_CTLR_SWAP
130u64 hwpoison_filter_memcg;
131EXPORT_SYMBOL_GPL(hwpoison_filter_memcg);
132static int hwpoison_filter_task(struct page *p)
133{
134    struct mem_cgroup *mem;
135    struct cgroup_subsys_state *css;
136    unsigned long ino;
137
138    if (!hwpoison_filter_memcg)
139        return 0;
140
141    mem = try_get_mem_cgroup_from_page(p);
142    if (!mem)
143        return -EINVAL;
144
145    css = mem_cgroup_css(mem);
146    /* root_mem_cgroup has NULL dentries */
147    if (!css->cgroup->dentry)
148        return -EINVAL;
149
150    ino = css->cgroup->dentry->d_inode->i_ino;
151    css_put(css);
152
153    if (ino != hwpoison_filter_memcg)
154        return -EINVAL;
155
156    return 0;
157}
158#else
159static int hwpoison_filter_task(struct page *p) { return 0; }
160#endif
161
162int hwpoison_filter(struct page *p)
163{
164    if (!hwpoison_filter_enable)
165        return 0;
166
167    if (hwpoison_filter_dev(p))
168        return -EINVAL;
169
170    if (hwpoison_filter_flags(p))
171        return -EINVAL;
172
173    if (hwpoison_filter_task(p))
174        return -EINVAL;
175
176    return 0;
177}
178#else
179int hwpoison_filter(struct page *p)
180{
181    return 0;
182}
183#endif
184
185EXPORT_SYMBOL_GPL(hwpoison_filter);
186
187/*
188 * Send all the processes who have the page mapped an ``action optional''
189 * signal.
190 */
191static int kill_proc_ao(struct task_struct *t, unsigned long addr, int trapno,
192            unsigned long pfn, struct page *page)
193{
194    struct siginfo si;
195    int ret;
196
197    printk(KERN_ERR
198        "MCE %#lx: Killing %s:%d early due to hardware memory corruption\n",
199        pfn, t->comm, t->pid);
200    si.si_signo = SIGBUS;
201    si.si_errno = 0;
202    si.si_code = BUS_MCEERR_AO;
203    si.si_addr = (void *)addr;
204#ifdef __ARCH_SI_TRAPNO
205    si.si_trapno = trapno;
206#endif
207    si.si_addr_lsb = compound_trans_order(compound_head(page)) + PAGE_SHIFT;
208    /*
209     * Don't use force here, it's convenient if the signal
210     * can be temporarily blocked.
211     * This could cause a loop when the user sets SIGBUS
212     * to SIG_IGN, but hopefully no one will do that?
213     */
214    ret = send_sig_info(SIGBUS, &si, t); /* synchronous? */
215    if (ret < 0)
216        printk(KERN_INFO "MCE: Error sending signal to %s:%d: %d\n",
217               t->comm, t->pid, ret);
218    return ret;
219}
220
221/*
222 * When a unknown page type is encountered drain as many buffers as possible
223 * in the hope to turn the page into a LRU or free page, which we can handle.
224 */
225void shake_page(struct page *p, int access)
226{
227    if (!PageSlab(p)) {
228        lru_add_drain_all();
229        if (PageLRU(p))
230            return;
231        drain_all_pages();
232        if (PageLRU(p) || is_free_buddy_page(p))
233            return;
234    }
235
236    /*
237     * Only call shrink_slab here (which would also shrink other caches) if
238     * access is not potentially fatal.
239     */
240    if (access) {
241        int nr;
242        do {
243            struct shrink_control shrink = {
244                .gfp_mask = GFP_KERNEL,
245            };
246
247            nr = shrink_slab(&shrink, 1000, 1000);
248            if (page_count(p) == 1)
249                break;
250        } while (nr > 10);
251    }
252}
253EXPORT_SYMBOL_GPL(shake_page);
254
255/*
256 * Kill all processes that have a poisoned page mapped and then isolate
257 * the page.
258 *
259 * General strategy:
260 * Find all processes having the page mapped and kill them.
261 * But we keep a page reference around so that the page is not
262 * actually freed yet.
263 * Then stash the page away
264 *
265 * There's no convenient way to get back to mapped processes
266 * from the VMAs. So do a brute-force search over all
267 * running processes.
268 *
269 * Remember that machine checks are not common (or rather
270 * if they are common you have other problems), so this shouldn't
271 * be a performance issue.
272 *
273 * Also there are some races possible while we get from the
274 * error detection to actually handle it.
275 */
276
277struct to_kill {
278    struct list_head nd;
279    struct task_struct *tsk;
280    unsigned long addr;
281    char addr_valid;
282};
283
284/*
285 * Failure handling: if we can't find or can't kill a process there's
286 * not much we can do. We just print a message and ignore otherwise.
287 */
288
289/*
290 * Schedule a process for later kill.
291 * Uses GFP_ATOMIC allocations to avoid potential recursions in the VM.
292 * TBD would GFP_NOIO be enough?
293 */
294static void add_to_kill(struct task_struct *tsk, struct page *p,
295               struct vm_area_struct *vma,
296               struct list_head *to_kill,
297               struct to_kill **tkc)
298{
299    struct to_kill *tk;
300
301    if (*tkc) {
302        tk = *tkc;
303        *tkc = NULL;
304    } else {
305        tk = kmalloc(sizeof(struct to_kill), GFP_ATOMIC);
306        if (!tk) {
307            printk(KERN_ERR
308        "MCE: Out of memory while machine check handling\n");
309            return;
310        }
311    }
312    tk->addr = page_address_in_vma(p, vma);
313    tk->addr_valid = 1;
314
315    /*
316     * In theory we don't have to kill when the page was
317     * munmaped. But it could be also a mremap. Since that's
318     * likely very rare kill anyways just out of paranoia, but use
319     * a SIGKILL because the error is not contained anymore.
320     */
321    if (tk->addr == -EFAULT) {
322        pr_info("MCE: Unable to find user space address %lx in %s\n",
323            page_to_pfn(p), tsk->comm);
324        tk->addr_valid = 0;
325    }
326    get_task_struct(tsk);
327    tk->tsk = tsk;
328    list_add_tail(&tk->nd, to_kill);
329}
330
331/*
332 * Kill the processes that have been collected earlier.
333 *
334 * Only do anything when DOIT is set, otherwise just free the list
335 * (this is used for clean pages which do not need killing)
336 * Also when FAIL is set do a force kill because something went
337 * wrong earlier.
338 */
339static void kill_procs_ao(struct list_head *to_kill, int doit, int trapno,
340              int fail, struct page *page, unsigned long pfn)
341{
342    struct to_kill *tk, *next;
343
344    list_for_each_entry_safe (tk, next, to_kill, nd) {
345        if (doit) {
346            /*
347             * In case something went wrong with munmapping
348             * make sure the process doesn't catch the
349             * signal and then access the memory. Just kill it.
350             */
351            if (fail || tk->addr_valid == 0) {
352                printk(KERN_ERR
353        "MCE %#lx: forcibly killing %s:%d because of failure to unmap corrupted page\n",
354                    pfn, tk->tsk->comm, tk->tsk->pid);
355                force_sig(SIGKILL, tk->tsk);
356            }
357
358            /*
359             * In theory the process could have mapped
360             * something else on the address in-between. We could
361             * check for that, but we need to tell the
362             * process anyways.
363             */
364            else if (kill_proc_ao(tk->tsk, tk->addr, trapno,
365                          pfn, page) < 0)
366                printk(KERN_ERR
367        "MCE %#lx: Cannot send advisory machine check signal to %s:%d\n",
368                    pfn, tk->tsk->comm, tk->tsk->pid);
369        }
370        put_task_struct(tk->tsk);
371        kfree(tk);
372    }
373}
374
375static int task_early_kill(struct task_struct *tsk)
376{
377    if (!tsk->mm)
378        return 0;
379    if (tsk->flags & PF_MCE_PROCESS)
380        return !!(tsk->flags & PF_MCE_EARLY);
381    return sysctl_memory_failure_early_kill;
382}
383
384/*
385 * Collect processes when the error hit an anonymous page.
386 */
387static void collect_procs_anon(struct page *page, struct list_head *to_kill,
388                  struct to_kill **tkc)
389{
390    struct vm_area_struct *vma;
391    struct task_struct *tsk;
392    struct anon_vma *av;
393
394    av = page_lock_anon_vma(page);
395    if (av == NULL) /* Not actually mapped anymore */
396        return;
397
398    read_lock(&tasklist_lock);
399    for_each_process (tsk) {
400        struct anon_vma_chain *vmac;
401
402        if (!task_early_kill(tsk))
403            continue;
404        list_for_each_entry(vmac, &av->head, same_anon_vma) {
405            vma = vmac->vma;
406            if (!page_mapped_in_vma(page, vma))
407                continue;
408            if (vma->vm_mm == tsk->mm)
409                add_to_kill(tsk, page, vma, to_kill, tkc);
410        }
411    }
412    read_unlock(&tasklist_lock);
413    page_unlock_anon_vma(av);
414}
415
416/*
417 * Collect processes when the error hit a file mapped page.
418 */
419static void collect_procs_file(struct page *page, struct list_head *to_kill,
420                  struct to_kill **tkc)
421{
422    struct vm_area_struct *vma;
423    struct task_struct *tsk;
424    struct prio_tree_iter iter;
425    struct address_space *mapping = page->mapping;
426
427    mutex_lock(&mapping->i_mmap_mutex);
428    read_lock(&tasklist_lock);
429    for_each_process(tsk) {
430        pgoff_t pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT);
431
432        if (!task_early_kill(tsk))
433            continue;
434
435        vma_prio_tree_foreach(vma, &iter, &mapping->i_mmap, pgoff,
436                      pgoff) {
437            /*
438             * Send early kill signal to tasks where a vma covers
439             * the page but the corrupted page is not necessarily
440             * mapped it in its pte.
441             * Assume applications who requested early kill want
442             * to be informed of all such data corruptions.
443             */
444            if (vma->vm_mm == tsk->mm)
445                add_to_kill(tsk, page, vma, to_kill, tkc);
446        }
447    }
448    read_unlock(&tasklist_lock);
449    mutex_unlock(&mapping->i_mmap_mutex);
450}
451
452/*
453 * Collect the processes who have the corrupted page mapped to kill.
454 * This is done in two steps for locking reasons.
455 * First preallocate one tokill structure outside the spin locks,
456 * so that we can kill at least one process reasonably reliable.
457 */
458static void collect_procs(struct page *page, struct list_head *tokill)
459{
460    struct to_kill *tk;
461
462    if (!page->mapping)
463        return;
464
465    tk = kmalloc(sizeof(struct to_kill), GFP_NOIO);
466    if (!tk)
467        return;
468    if (PageAnon(page))
469        collect_procs_anon(page, tokill, &tk);
470    else
471        collect_procs_file(page, tokill, &tk);
472    kfree(tk);
473}
474
475/*
476 * Error handlers for various types of pages.
477 */
478
479enum outcome {
480    IGNORED, /* Error: cannot be handled */
481    FAILED, /* Error: handling failed */
482    DELAYED, /* Will be handled later */
483    RECOVERED, /* Successfully recovered */
484};
485
486static const char *action_name[] = {
487    [IGNORED] = "Ignored",
488    [FAILED] = "Failed",
489    [DELAYED] = "Delayed",
490    [RECOVERED] = "Recovered",
491};
492
493/*
494 * XXX: It is possible that a page is isolated from LRU cache,
495 * and then kept in swap cache or failed to remove from page cache.
496 * The page count will stop it from being freed by unpoison.
497 * Stress tests should be aware of this memory leak problem.
498 */
499static int delete_from_lru_cache(struct page *p)
500{
501    if (!isolate_lru_page(p)) {
502        /*
503         * Clear sensible page flags, so that the buddy system won't
504         * complain when the page is unpoison-and-freed.
505         */
506        ClearPageActive(p);
507        ClearPageUnevictable(p);
508        /*
509         * drop the page count elevated by isolate_lru_page()
510         */
511        page_cache_release(p);
512        return 0;
513    }
514    return -EIO;
515}
516
517/*
518 * Error hit kernel page.
519 * Do nothing, try to be lucky and not touch this instead. For a few cases we
520 * could be more sophisticated.
521 */
522static int me_kernel(struct page *p, unsigned long pfn)
523{
524    return IGNORED;
525}
526
527/*
528 * Page in unknown state. Do nothing.
529 */
530static int me_unknown(struct page *p, unsigned long pfn)
531{
532    printk(KERN_ERR "MCE %#lx: Unknown page state\n", pfn);
533    return FAILED;
534}
535
536/*
537 * Clean (or cleaned) page cache page.
538 */
539static int me_pagecache_clean(struct page *p, unsigned long pfn)
540{
541    int err;
542    int ret = FAILED;
543    struct address_space *mapping;
544
545    delete_from_lru_cache(p);
546
547    /*
548     * For anonymous pages we're done the only reference left
549     * should be the one m_f() holds.
550     */
551    if (PageAnon(p))
552        return RECOVERED;
553
554    /*
555     * Now truncate the page in the page cache. This is really
556     * more like a "temporary hole punch"
557     * Don't do this for block devices when someone else
558     * has a reference, because it could be file system metadata
559     * and that's not safe to truncate.
560     */
561    mapping = page_mapping(p);
562    if (!mapping) {
563        /*
564         * Page has been teared down in the meanwhile
565         */
566        return FAILED;
567    }
568
569    /*
570     * Truncation is a bit tricky. Enable it per file system for now.
571     *
572     * Open: to take i_mutex or not for this? Right now we don't.
573     */
574    if (mapping->a_ops->error_remove_page) {
575        err = mapping->a_ops->error_remove_page(mapping, p);
576        if (err != 0) {
577            printk(KERN_INFO "MCE %#lx: Failed to punch page: %d\n",
578                    pfn, err);
579        } else if (page_has_private(p) &&
580                !try_to_release_page(p, GFP_NOIO)) {
581            pr_info("MCE %#lx: failed to release buffers\n", pfn);
582        } else {
583            ret = RECOVERED;
584        }
585    } else {
586        /*
587         * If the file system doesn't support it just invalidate
588         * This fails on dirty or anything with private pages
589         */
590        if (invalidate_inode_page(p))
591            ret = RECOVERED;
592        else
593            printk(KERN_INFO "MCE %#lx: Failed to invalidate\n",
594                pfn);
595    }
596    return ret;
597}
598
599/*
600 * Dirty cache page page
601 * Issues: when the error hit a hole page the error is not properly
602 * propagated.
603 */
604static int me_pagecache_dirty(struct page *p, unsigned long pfn)
605{
606    struct address_space *mapping = page_mapping(p);
607
608    SetPageError(p);
609    /* TBD: print more information about the file. */
610    if (mapping) {
611        /*
612         * IO error will be reported by write(), fsync(), etc.
613         * who check the mapping.
614         * This way the application knows that something went
615         * wrong with its dirty file data.
616         *
617         * There's one open issue:
618         *
619         * The EIO will be only reported on the next IO
620         * operation and then cleared through the IO map.
621         * Normally Linux has two mechanisms to pass IO error
622         * first through the AS_EIO flag in the address space
623         * and then through the PageError flag in the page.
624         * Since we drop pages on memory failure handling the
625         * only mechanism open to use is through AS_AIO.
626         *
627         * This has the disadvantage that it gets cleared on
628         * the first operation that returns an error, while
629         * the PageError bit is more sticky and only cleared
630         * when the page is reread or dropped. If an
631         * application assumes it will always get error on
632         * fsync, but does other operations on the fd before
633         * and the page is dropped between then the error
634         * will not be properly reported.
635         *
636         * This can already happen even without hwpoisoned
637         * pages: first on metadata IO errors (which only
638         * report through AS_EIO) or when the page is dropped
639         * at the wrong time.
640         *
641         * So right now we assume that the application DTRT on
642         * the first EIO, but we're not worse than other parts
643         * of the kernel.
644         */
645        mapping_set_error(mapping, EIO);
646    }
647
648    return me_pagecache_clean(p, pfn);
649}
650
651/*
652 * Clean and dirty swap cache.
653 *
654 * Dirty swap cache page is tricky to handle. The page could live both in page
655 * cache and swap cache(ie. page is freshly swapped in). So it could be
656 * referenced concurrently by 2 types of PTEs:
657 * normal PTEs and swap PTEs. We try to handle them consistently by calling
658 * try_to_unmap(TTU_IGNORE_HWPOISON) to convert the normal PTEs to swap PTEs,
659 * and then
660 * - clear dirty bit to prevent IO
661 * - remove from LRU
662 * - but keep in the swap cache, so that when we return to it on
663 * a later page fault, we know the application is accessing
664 * corrupted data and shall be killed (we installed simple
665 * interception code in do_swap_page to catch it).
666 *
667 * Clean swap cache pages can be directly isolated. A later page fault will
668 * bring in the known good data from disk.
669 */
670static int me_swapcache_dirty(struct page *p, unsigned long pfn)
671{
672    ClearPageDirty(p);
673    /* Trigger EIO in shmem: */
674    ClearPageUptodate(p);
675
676    if (!delete_from_lru_cache(p))
677        return DELAYED;
678    else
679        return FAILED;
680}
681
682static int me_swapcache_clean(struct page *p, unsigned long pfn)
683{
684    delete_from_swap_cache(p);
685
686    if (!delete_from_lru_cache(p))
687        return RECOVERED;
688    else
689        return FAILED;
690}
691
692/*
693 * Huge pages. Needs work.
694 * Issues:
695 * - Error on hugepage is contained in hugepage unit (not in raw page unit.)
696 * To narrow down kill region to one page, we need to break up pmd.
697 */
698static int me_huge_page(struct page *p, unsigned long pfn)
699{
700    int res = 0;
701    struct page *hpage = compound_head(p);
702    /*
703     * We can safely recover from error on free or reserved (i.e.
704     * not in-use) hugepage by dequeuing it from freelist.
705     * To check whether a hugepage is in-use or not, we can't use
706     * page->lru because it can be used in other hugepage operations,
707     * such as __unmap_hugepage_range() and gather_surplus_pages().
708     * So instead we use page_mapping() and PageAnon().
709     * We assume that this function is called with page lock held,
710     * so there is no race between isolation and mapping/unmapping.
711     */
712    if (!(page_mapping(hpage) || PageAnon(hpage))) {
713        res = dequeue_hwpoisoned_huge_page(hpage);
714        if (!res)
715            return RECOVERED;
716    }
717    return DELAYED;
718}
719
720/*
721 * Various page states we can handle.
722 *
723 * A page state is defined by its current page->flags bits.
724 * The table matches them in order and calls the right handler.
725 *
726 * This is quite tricky because we can access page at any time
727 * in its live cycle, so all accesses have to be extremely careful.
728 *
729 * This is not complete. More states could be added.
730 * For any missing state don't attempt recovery.
731 */
732
733#define dirty (1UL << PG_dirty)
734#define sc (1UL << PG_swapcache)
735#define unevict (1UL << PG_unevictable)
736#define mlock (1UL << PG_mlocked)
737#define writeback (1UL << PG_writeback)
738#define lru (1UL << PG_lru)
739#define swapbacked (1UL << PG_swapbacked)
740#define head (1UL << PG_head)
741#define tail (1UL << PG_tail)
742#define compound (1UL << PG_compound)
743#define slab (1UL << PG_slab)
744#define reserved (1UL << PG_reserved)
745
746static struct page_state {
747    unsigned long mask;
748    unsigned long res;
749    char *msg;
750    int (*action)(struct page *p, unsigned long pfn);
751} error_states[] = {
752    { reserved, reserved, "reserved kernel", me_kernel },
753    /*
754     * free pages are specially detected outside this table:
755     * PG_buddy pages only make a small fraction of all free pages.
756     */
757
758    /*
759     * Could in theory check if slab page is free or if we can drop
760     * currently unused objects without touching them. But just
761     * treat it as standard kernel for now.
762     */
763    { slab, slab, "kernel slab", me_kernel },
764
765#ifdef CONFIG_PAGEFLAGS_EXTENDED
766    { head, head, "huge", me_huge_page },
767    { tail, tail, "huge", me_huge_page },
768#else
769    { compound, compound, "huge", me_huge_page },
770#endif
771
772    { sc|dirty, sc|dirty, "swapcache", me_swapcache_dirty },
773    { sc|dirty, sc, "swapcache", me_swapcache_clean },
774
775    { unevict|dirty, unevict|dirty, "unevictable LRU", me_pagecache_dirty},
776    { unevict, unevict, "unevictable LRU", me_pagecache_clean},
777
778    { mlock|dirty, mlock|dirty, "mlocked LRU", me_pagecache_dirty },
779    { mlock, mlock, "mlocked LRU", me_pagecache_clean },
780
781    { lru|dirty, lru|dirty, "LRU", me_pagecache_dirty },
782    { lru|dirty, lru, "clean LRU", me_pagecache_clean },
783
784    /*
785     * Catchall entry: must be at end.
786     */
787    { 0, 0, "unknown page state", me_unknown },
788};
789
790#undef dirty
791#undef sc
792#undef unevict
793#undef mlock
794#undef writeback
795#undef lru
796#undef swapbacked
797#undef head
798#undef tail
799#undef compound
800#undef slab
801#undef reserved
802
803static void action_result(unsigned long pfn, char *msg, int result)
804{
805    struct page *page = pfn_to_page(pfn);
806
807    printk(KERN_ERR "MCE %#lx: %s%s page recovery: %s\n",
808        pfn,
809        PageDirty(page) ? "dirty " : "",
810        msg, action_name[result]);
811}
812
813static int page_action(struct page_state *ps, struct page *p,
814            unsigned long pfn)
815{
816    int result;
817    int count;
818
819    result = ps->action(p, pfn);
820    action_result(pfn, ps->msg, result);
821
822    count = page_count(p) - 1;
823    if (ps->action == me_swapcache_dirty && result == DELAYED)
824        count--;
825    if (count != 0) {
826        printk(KERN_ERR
827               "MCE %#lx: %s page still referenced by %d users\n",
828               pfn, ps->msg, count);
829        result = FAILED;
830    }
831
832    /* Could do more checks here if page looks ok */
833    /*
834     * Could adjust zone counters here to correct for the missing page.
835     */
836
837    return (result == RECOVERED || result == DELAYED) ? 0 : -EBUSY;
838}
839
840/*
841 * Do all that is necessary to remove user space mappings. Unmap
842 * the pages and send SIGBUS to the processes if the data was dirty.
843 */
844static int hwpoison_user_mappings(struct page *p, unsigned long pfn,
845                  int trapno)
846{
847    enum ttu_flags ttu = TTU_UNMAP | TTU_IGNORE_MLOCK | TTU_IGNORE_ACCESS;
848    struct address_space *mapping;
849    LIST_HEAD(tokill);
850    int ret;
851    int kill = 1;
852    struct page *hpage = compound_head(p);
853    struct page *ppage;
854
855    if (PageReserved(p) || PageSlab(p))
856        return SWAP_SUCCESS;
857
858    /*
859     * This check implies we don't kill processes if their pages
860     * are in the swap cache early. Those are always late kills.
861     */
862    if (!page_mapped(hpage))
863        return SWAP_SUCCESS;
864
865    if (PageKsm(p))
866        return SWAP_FAIL;
867
868    if (PageSwapCache(p)) {
869        printk(KERN_ERR
870               "MCE %#lx: keeping poisoned page in swap cache\n", pfn);
871        ttu |= TTU_IGNORE_HWPOISON;
872    }
873
874    /*
875     * Propagate the dirty bit from PTEs to struct page first, because we
876     * need this to decide if we should kill or just drop the page.
877     * XXX: the dirty test could be racy: set_page_dirty() may not always
878     * be called inside page lock (it's recommended but not enforced).
879     */
880    mapping = page_mapping(hpage);
881    if (!PageDirty(hpage) && mapping &&
882        mapping_cap_writeback_dirty(mapping)) {
883        if (page_mkclean(hpage)) {
884            SetPageDirty(hpage);
885        } else {
886            kill = 0;
887            ttu |= TTU_IGNORE_HWPOISON;
888            printk(KERN_INFO
889    "MCE %#lx: corrupted page was clean: dropped without side effects\n",
890                pfn);
891        }
892    }
893
894    /*
895     * ppage: poisoned page
896     * if p is regular page(4k page)
897     * ppage == real poisoned page;
898     * else p is hugetlb or THP, ppage == head page.
899     */
900    ppage = hpage;
901
902    if (PageTransHuge(hpage)) {
903        /*
904         * Verify that this isn't a hugetlbfs head page, the check for
905         * PageAnon is just for avoid tripping a split_huge_page
906         * internal debug check, as split_huge_page refuses to deal with
907         * anything that isn't an anon page. PageAnon can't go away fro
908         * under us because we hold a refcount on the hpage, without a
909         * refcount on the hpage. split_huge_page can't be safely called
910         * in the first place, having a refcount on the tail isn't
911         * enough * to be safe.
912         */
913        if (!PageHuge(hpage) && PageAnon(hpage)) {
914            if (unlikely(split_huge_page(hpage))) {
915                /*
916                 * FIXME: if splitting THP is failed, it is
917                 * better to stop the following operation rather
918                 * than causing panic by unmapping. System might
919                 * survive if the page is freed later.
920                 */
921                printk(KERN_INFO
922                    "MCE %#lx: failed to split THP\n", pfn);
923
924                BUG_ON(!PageHWPoison(p));
925                return SWAP_FAIL;
926            }
927            /* THP is split, so ppage should be the real poisoned page. */
928            ppage = p;
929        }
930    }
931
932    /*
933     * First collect all the processes that have the page
934     * mapped in dirty form. This has to be done before try_to_unmap,
935     * because ttu takes the rmap data structures down.
936     *
937     * Error handling: We ignore errors here because
938     * there's nothing that can be done.
939     */
940    if (kill)
941        collect_procs(ppage, &tokill);
942
943    if (hpage != ppage)
944        lock_page(ppage);
945
946    ret = try_to_unmap(ppage, ttu);
947    if (ret != SWAP_SUCCESS)
948        printk(KERN_ERR "MCE %#lx: failed to unmap page (mapcount=%d)\n",
949                pfn, page_mapcount(ppage));
950
951    if (hpage != ppage)
952        unlock_page(ppage);
953
954    /*
955     * Now that the dirty bit has been propagated to the
956     * struct page and all unmaps done we can decide if
957     * killing is needed or not. Only kill when the page
958     * was dirty, otherwise the tokill list is merely
959     * freed. When there was a problem unmapping earlier
960     * use a more force-full uncatchable kill to prevent
961     * any accesses to the poisoned memory.
962     */
963    kill_procs_ao(&tokill, !!PageDirty(ppage), trapno,
964              ret != SWAP_SUCCESS, p, pfn);
965
966    return ret;
967}
968
969static void set_page_hwpoison_huge_page(struct page *hpage)
970{
971    int i;
972    int nr_pages = 1 << compound_trans_order(hpage);
973    for (i = 0; i < nr_pages; i++)
974        SetPageHWPoison(hpage + i);
975}
976
977static void clear_page_hwpoison_huge_page(struct page *hpage)
978{
979    int i;
980    int nr_pages = 1 << compound_trans_order(hpage);
981    for (i = 0; i < nr_pages; i++)
982        ClearPageHWPoison(hpage + i);
983}
984
985int __memory_failure(unsigned long pfn, int trapno, int flags)
986{
987    struct page_state *ps;
988    struct page *p;
989    struct page *hpage;
990    int res;
991    unsigned int nr_pages;
992
993    if (!sysctl_memory_failure_recovery)
994        panic("Memory failure from trap %d on page %lx", trapno, pfn);
995
996    if (!pfn_valid(pfn)) {
997        printk(KERN_ERR
998               "MCE %#lx: memory outside kernel control\n",
999               pfn);
1000        return -ENXIO;
1001    }
1002
1003    p = pfn_to_page(pfn);
1004    hpage = compound_head(p);
1005    if (TestSetPageHWPoison(p)) {
1006        printk(KERN_ERR "MCE %#lx: already hardware poisoned\n", pfn);
1007        return 0;
1008    }
1009
1010    nr_pages = 1 << compound_trans_order(hpage);
1011    atomic_long_add(nr_pages, &mce_bad_pages);
1012
1013    /*
1014     * We need/can do nothing about count=0 pages.
1015     * 1) it's a free page, and therefore in safe hand:
1016     * prep_new_page() will be the gate keeper.
1017     * 2) it's a free hugepage, which is also safe:
1018     * an affected hugepage will be dequeued from hugepage freelist,
1019     * so there's no concern about reusing it ever after.
1020     * 3) it's part of a non-compound high order page.
1021     * Implies some kernel user: cannot stop them from
1022     * R/W the page; let's pray that the page has been
1023     * used and will be freed some time later.
1024     * In fact it's dangerous to directly bump up page count from 0,
1025     * that may make page_freeze_refs()/page_unfreeze_refs() mismatch.
1026     */
1027    if (!(flags & MF_COUNT_INCREASED) &&
1028        !get_page_unless_zero(hpage)) {
1029        if (is_free_buddy_page(p)) {
1030            action_result(pfn, "free buddy", DELAYED);
1031            return 0;
1032        } else if (PageHuge(hpage)) {
1033            /*
1034             * Check "just unpoisoned", "filter hit", and
1035             * "race with other subpage."
1036             */
1037            lock_page(hpage);
1038            if (!PageHWPoison(hpage)
1039                || (hwpoison_filter(p) && TestClearPageHWPoison(p))
1040                || (p != hpage && TestSetPageHWPoison(hpage))) {
1041                atomic_long_sub(nr_pages, &mce_bad_pages);
1042                return 0;
1043            }
1044            set_page_hwpoison_huge_page(hpage);
1045            res = dequeue_hwpoisoned_huge_page(hpage);
1046            action_result(pfn, "free huge",
1047                      res ? IGNORED : DELAYED);
1048            unlock_page(hpage);
1049            return res;
1050        } else {
1051            action_result(pfn, "high order kernel", IGNORED);
1052            return -EBUSY;
1053        }
1054    }
1055
1056    /*
1057     * We ignore non-LRU pages for good reasons.
1058     * - PG_locked is only well defined for LRU pages and a few others
1059     * - to avoid races with __set_page_locked()
1060     * - to avoid races with __SetPageSlab*() (and more non-atomic ops)
1061     * The check (unnecessarily) ignores LRU pages being isolated and
1062     * walked by the page reclaim code, however that's not a big loss.
1063     */
1064    if (!PageHuge(p) && !PageTransCompound(p)) {
1065        if (!PageLRU(p))
1066            shake_page(p, 0);
1067        if (!PageLRU(p)) {
1068            /*
1069             * shake_page could have turned it free.
1070             */
1071            if (is_free_buddy_page(p)) {
1072                action_result(pfn, "free buddy, 2nd try",
1073                        DELAYED);
1074                return 0;
1075            }
1076            action_result(pfn, "non LRU", IGNORED);
1077            put_page(p);
1078            return -EBUSY;
1079        }
1080    }
1081
1082    /*
1083     * Lock the page and wait for writeback to finish.
1084     * It's very difficult to mess with pages currently under IO
1085     * and in many cases impossible, so we just avoid it here.
1086     */
1087    lock_page(hpage);
1088
1089    /*
1090     * unpoison always clear PG_hwpoison inside page lock
1091     */
1092    if (!PageHWPoison(p)) {
1093        printk(KERN_ERR "MCE %#lx: just unpoisoned\n", pfn);
1094        res = 0;
1095        goto out;
1096    }
1097    if (hwpoison_filter(p)) {
1098        if (TestClearPageHWPoison(p))
1099            atomic_long_sub(nr_pages, &mce_bad_pages);
1100        unlock_page(hpage);
1101        put_page(hpage);
1102        return 0;
1103    }
1104
1105    /*
1106     * For error on the tail page, we should set PG_hwpoison
1107     * on the head page to show that the hugepage is hwpoisoned
1108     */
1109    if (PageHuge(p) && PageTail(p) && TestSetPageHWPoison(hpage)) {
1110        action_result(pfn, "hugepage already hardware poisoned",
1111                IGNORED);
1112        unlock_page(hpage);
1113        put_page(hpage);
1114        return 0;
1115    }
1116    /*
1117     * Set PG_hwpoison on all pages in an error hugepage,
1118     * because containment is done in hugepage unit for now.
1119     * Since we have done TestSetPageHWPoison() for the head page with
1120     * page lock held, we can safely set PG_hwpoison bits on tail pages.
1121     */
1122    if (PageHuge(p))
1123        set_page_hwpoison_huge_page(hpage);
1124
1125    wait_on_page_writeback(p);
1126
1127    /*
1128     * Now take care of user space mappings.
1129     * Abort on fail: __delete_from_page_cache() assumes unmapped page.
1130     */
1131    if (hwpoison_user_mappings(p, pfn, trapno) != SWAP_SUCCESS) {
1132        printk(KERN_ERR "MCE %#lx: cannot unmap page, give up\n", pfn);
1133        res = -EBUSY;
1134        goto out;
1135    }
1136
1137    /*
1138     * Torn down by someone else?
1139     */
1140    if (PageLRU(p) && !PageSwapCache(p) && p->mapping == NULL) {
1141        action_result(pfn, "already truncated LRU", IGNORED);
1142        res = -EBUSY;
1143        goto out;
1144    }
1145
1146    res = -EBUSY;
1147    for (ps = error_states;; ps++) {
1148        if ((p->flags & ps->mask) == ps->res) {
1149            res = page_action(ps, p, pfn);
1150            break;
1151        }
1152    }
1153out:
1154    unlock_page(hpage);
1155    return res;
1156}
1157EXPORT_SYMBOL_GPL(__memory_failure);
1158
1159/**
1160 * memory_failure - Handle memory failure of a page.
1161 * @pfn: Page Number of the corrupted page
1162 * @trapno: Trap number reported in the signal to user space.
1163 *
1164 * This function is called by the low level machine check code
1165 * of an architecture when it detects hardware memory corruption
1166 * of a page. It tries its best to recover, which includes
1167 * dropping pages, killing processes etc.
1168 *
1169 * The function is primarily of use for corruptions that
1170 * happen outside the current execution context (e.g. when
1171 * detected by a background scrubber)
1172 *
1173 * Must run in process context (e.g. a work queue) with interrupts
1174 * enabled and no spinlocks hold.
1175 */
1176void memory_failure(unsigned long pfn, int trapno)
1177{
1178    __memory_failure(pfn, trapno, 0);
1179}
1180
1181/**
1182 * unpoison_memory - Unpoison a previously poisoned page
1183 * @pfn: Page number of the to be unpoisoned page
1184 *
1185 * Software-unpoison a page that has been poisoned by
1186 * memory_failure() earlier.
1187 *
1188 * This is only done on the software-level, so it only works
1189 * for linux injected failures, not real hardware failures
1190 *
1191 * Returns 0 for success, otherwise -errno.
1192 */
1193int unpoison_memory(unsigned long pfn)
1194{
1195    struct page *page;
1196    struct page *p;
1197    int freeit = 0;
1198    unsigned int nr_pages;
1199
1200    if (!pfn_valid(pfn))
1201        return -ENXIO;
1202
1203    p = pfn_to_page(pfn);
1204    page = compound_head(p);
1205
1206    if (!PageHWPoison(p)) {
1207        pr_info("MCE: Page was already unpoisoned %#lx\n", pfn);
1208        return 0;
1209    }
1210
1211    nr_pages = 1 << compound_trans_order(page);
1212
1213    if (!get_page_unless_zero(page)) {
1214        /*
1215         * Since HWPoisoned hugepage should have non-zero refcount,
1216         * race between memory failure and unpoison seems to happen.
1217         * In such case unpoison fails and memory failure runs
1218         * to the end.
1219         */
1220        if (PageHuge(page)) {
1221            pr_debug("MCE: Memory failure is now running on free hugepage %#lx\n", pfn);
1222            return 0;
1223        }
1224        if (TestClearPageHWPoison(p))
1225            atomic_long_sub(nr_pages, &mce_bad_pages);
1226        pr_info("MCE: Software-unpoisoned free page %#lx\n", pfn);
1227        return 0;
1228    }
1229
1230    lock_page(page);
1231    /*
1232     * This test is racy because PG_hwpoison is set outside of page lock.
1233     * That's acceptable because that won't trigger kernel panic. Instead,
1234     * the PG_hwpoison page will be caught and isolated on the entrance to
1235     * the free buddy page pool.
1236     */
1237    if (TestClearPageHWPoison(page)) {
1238        pr_info("MCE: Software-unpoisoned page %#lx\n", pfn);
1239        atomic_long_sub(nr_pages, &mce_bad_pages);
1240        freeit = 1;
1241        if (PageHuge(page))
1242            clear_page_hwpoison_huge_page(page);
1243    }
1244    unlock_page(page);
1245
1246    put_page(page);
1247    if (freeit)
1248        put_page(page);
1249
1250    return 0;
1251}
1252EXPORT_SYMBOL(unpoison_memory);
1253
1254static struct page *new_page(struct page *p, unsigned long private, int **x)
1255{
1256    int nid = page_to_nid(p);
1257    if (PageHuge(p))
1258        return alloc_huge_page_node(page_hstate(compound_head(p)),
1259                           nid);
1260    else
1261        return alloc_pages_exact_node(nid, GFP_HIGHUSER_MOVABLE, 0);
1262}
1263
1264/*
1265 * Safely get reference count of an arbitrary page.
1266 * Returns 0 for a free page, -EIO for a zero refcount page
1267 * that is not free, and 1 for any other page type.
1268 * For 1 the page is returned with increased page count, otherwise not.
1269 */
1270static int get_any_page(struct page *p, unsigned long pfn, int flags)
1271{
1272    int ret;
1273
1274    if (flags & MF_COUNT_INCREASED)
1275        return 1;
1276
1277    /*
1278     * The lock_memory_hotplug prevents a race with memory hotplug.
1279     * This is a big hammer, a better would be nicer.
1280     */
1281    lock_memory_hotplug();
1282
1283    /*
1284     * Isolate the page, so that it doesn't get reallocated if it
1285     * was free.
1286     */
1287    set_migratetype_isolate(p);
1288    /*
1289     * When the target page is a free hugepage, just remove it
1290     * from free hugepage list.
1291     */
1292    if (!get_page_unless_zero(compound_head(p))) {
1293        if (PageHuge(p)) {
1294            pr_info("get_any_page: %#lx free huge page\n", pfn);
1295            ret = dequeue_hwpoisoned_huge_page(compound_head(p));
1296        } else if (is_free_buddy_page(p)) {
1297            pr_info("get_any_page: %#lx free buddy page\n", pfn);
1298            /* Set hwpoison bit while page is still isolated */
1299            SetPageHWPoison(p);
1300            ret = 0;
1301        } else {
1302            pr_info("get_any_page: %#lx: unknown zero refcount page type %lx\n",
1303                pfn, p->flags);
1304            ret = -EIO;
1305        }
1306    } else {
1307        /* Not a free page */
1308        ret = 1;
1309    }
1310    unset_migratetype_isolate(p);
1311    unlock_memory_hotplug();
1312    return ret;
1313}
1314
1315static int soft_offline_huge_page(struct page *page, int flags)
1316{
1317    int ret;
1318    unsigned long pfn = page_to_pfn(page);
1319    struct page *hpage = compound_head(page);
1320    LIST_HEAD(pagelist);
1321
1322    ret = get_any_page(page, pfn, flags);
1323    if (ret < 0)
1324        return ret;
1325    if (ret == 0)
1326        goto done;
1327
1328    if (PageHWPoison(hpage)) {
1329        put_page(hpage);
1330        pr_debug("soft offline: %#lx hugepage already poisoned\n", pfn);
1331        return -EBUSY;
1332    }
1333
1334    /* Keep page count to indicate a given hugepage is isolated. */
1335
1336    list_add(&hpage->lru, &pagelist);
1337    ret = migrate_huge_pages(&pagelist, new_page, MPOL_MF_MOVE_ALL, 0,
1338                true);
1339    if (ret) {
1340        struct page *page1, *page2;
1341        list_for_each_entry_safe(page1, page2, &pagelist, lru)
1342            put_page(page1);
1343
1344        pr_debug("soft offline: %#lx: migration failed %d, type %lx\n",
1345             pfn, ret, page->flags);
1346        if (ret > 0)
1347            ret = -EIO;
1348        return ret;
1349    }
1350done:
1351    if (!PageHWPoison(hpage))
1352        atomic_long_add(1 << compound_trans_order(hpage), &mce_bad_pages);
1353    set_page_hwpoison_huge_page(hpage);
1354    dequeue_hwpoisoned_huge_page(hpage);
1355    /* keep elevated page count for bad page */
1356    return ret;
1357}
1358
1359/**
1360 * soft_offline_page - Soft offline a page.
1361 * @page: page to offline
1362 * @flags: flags. Same as memory_failure().
1363 *
1364 * Returns 0 on success, otherwise negated errno.
1365 *
1366 * Soft offline a page, by migration or invalidation,
1367 * without killing anything. This is for the case when
1368 * a page is not corrupted yet (so it's still valid to access),
1369 * but has had a number of corrected errors and is better taken
1370 * out.
1371 *
1372 * The actual policy on when to do that is maintained by
1373 * user space.
1374 *
1375 * This should never impact any application or cause data loss,
1376 * however it might take some time.
1377 *
1378 * This is not a 100% solution for all memory, but tries to be
1379 * ``good enough'' for the majority of memory.
1380 */
1381int soft_offline_page(struct page *page, int flags)
1382{
1383    int ret;
1384    unsigned long pfn = page_to_pfn(page);
1385
1386    if (PageHuge(page))
1387        return soft_offline_huge_page(page, flags);
1388
1389    ret = get_any_page(page, pfn, flags);
1390    if (ret < 0)
1391        return ret;
1392    if (ret == 0)
1393        goto done;
1394
1395    /*
1396     * Page cache page we can handle?
1397     */
1398    if (!PageLRU(page)) {
1399        /*
1400         * Try to free it.
1401         */
1402        put_page(page);
1403        shake_page(page, 1);
1404
1405        /*
1406         * Did it turn free?
1407         */
1408        ret = get_any_page(page, pfn, 0);
1409        if (ret < 0)
1410            return ret;
1411        if (ret == 0)
1412            goto done;
1413    }
1414    if (!PageLRU(page)) {
1415        pr_info("soft_offline: %#lx: unknown non LRU page type %lx\n",
1416                pfn, page->flags);
1417        return -EIO;
1418    }
1419
1420    lock_page(page);
1421    wait_on_page_writeback(page);
1422
1423    /*
1424     * Synchronized using the page lock with memory_failure()
1425     */
1426    if (PageHWPoison(page)) {
1427        unlock_page(page);
1428        put_page(page);
1429        pr_info("soft offline: %#lx page already poisoned\n", pfn);
1430        return -EBUSY;
1431    }
1432
1433    /*
1434     * Try to invalidate first. This should work for
1435     * non dirty unmapped page cache pages.
1436     */
1437    ret = invalidate_inode_page(page);
1438    unlock_page(page);
1439    /*
1440     * RED-PEN would be better to keep it isolated here, but we
1441     * would need to fix isolation locking first.
1442     */
1443    if (ret == 1) {
1444        put_page(page);
1445        ret = 0;
1446        pr_info("soft_offline: %#lx: invalidated\n", pfn);
1447        goto done;
1448    }
1449
1450    /*
1451     * Simple invalidation didn't work.
1452     * Try to migrate to a new page instead. migrate.c
1453     * handles a large number of cases for us.
1454     */
1455    ret = isolate_lru_page(page);
1456    /*
1457     * Drop page reference which is came from get_any_page()
1458     * successful isolate_lru_page() already took another one.
1459     */
1460    put_page(page);
1461    if (!ret) {
1462        LIST_HEAD(pagelist);
1463        inc_zone_page_state(page, NR_ISOLATED_ANON +
1464                        page_is_file_cache(page));
1465        list_add(&page->lru, &pagelist);
1466        ret = migrate_pages(&pagelist, new_page, MPOL_MF_MOVE_ALL,
1467                                0, true);
1468        if (ret) {
1469            putback_lru_pages(&pagelist);
1470            pr_info("soft offline: %#lx: migration failed %d, type %lx\n",
1471                pfn, ret, page->flags);
1472            if (ret > 0)
1473                ret = -EIO;
1474        }
1475    } else {
1476        pr_info("soft offline: %#lx: isolation failed: %d, page count %d, type %lx\n",
1477                pfn, ret, page_count(page), page->flags);
1478    }
1479    if (ret)
1480        return ret;
1481
1482done:
1483    atomic_long_add(1, &mce_bad_pages);
1484    SetPageHWPoison(page);
1485    /* keep elevated page count for bad page */
1486    return ret;
1487}
1488

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