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Linux/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  * It can be very tempting to add handling for obscure cases here.
 25  * In general any code for handling new cases should only be added iff:
 26  * - You know how to test it.
 27  * - You have a test that can be added to mce-test
 28  *   https://git.kernel.org/cgit/utils/cpu/mce/mce-test.git/
 29  * - The case actually shows up as a frequent (top 10) page state in
 30  *   tools/vm/page-types when running a real workload.
 31  * 
 32  * There are several operations here with exponential complexity because
 33  * of unsuitable VM data structures. For example the operation to map back 
 34  * from RMAP chains to processes has to walk the complete process list and 
 35  * has non linear complexity with the number. But since memory corruptions
 36  * are rare we hope to get away with this. This avoids impacting the core 
 37  * VM.
 38  */
 39 #include <linux/kernel.h>
 40 #include <linux/mm.h>
 41 #include <linux/page-flags.h>
 42 #include <linux/kernel-page-flags.h>
 43 #include <linux/sched.h>
 44 #include <linux/ksm.h>
 45 #include <linux/rmap.h>
 46 #include <linux/export.h>
 47 #include <linux/pagemap.h>
 48 #include <linux/swap.h>
 49 #include <linux/backing-dev.h>
 50 #include <linux/migrate.h>
 51 #include <linux/page-isolation.h>
 52 #include <linux/suspend.h>
 53 #include <linux/slab.h>
 54 #include <linux/swapops.h>
 55 #include <linux/hugetlb.h>
 56 #include <linux/memory_hotplug.h>
 57 #include <linux/mm_inline.h>
 58 #include <linux/kfifo.h>
 59 #include <linux/ratelimit.h>
 60 #include "internal.h"
 61 #include "ras/ras_event.h"
 62 
 63 int sysctl_memory_failure_early_kill __read_mostly = 0;
 64 
 65 int sysctl_memory_failure_recovery __read_mostly = 1;
 66 
 67 atomic_long_t num_poisoned_pages __read_mostly = ATOMIC_LONG_INIT(0);
 68 
 69 #if defined(CONFIG_HWPOISON_INJECT) || defined(CONFIG_HWPOISON_INJECT_MODULE)
 70 
 71 u32 hwpoison_filter_enable = 0;
 72 u32 hwpoison_filter_dev_major = ~0U;
 73 u32 hwpoison_filter_dev_minor = ~0U;
 74 u64 hwpoison_filter_flags_mask;
 75 u64 hwpoison_filter_flags_value;
 76 EXPORT_SYMBOL_GPL(hwpoison_filter_enable);
 77 EXPORT_SYMBOL_GPL(hwpoison_filter_dev_major);
 78 EXPORT_SYMBOL_GPL(hwpoison_filter_dev_minor);
 79 EXPORT_SYMBOL_GPL(hwpoison_filter_flags_mask);
 80 EXPORT_SYMBOL_GPL(hwpoison_filter_flags_value);
 81 
 82 static int hwpoison_filter_dev(struct page *p)
 83 {
 84         struct address_space *mapping;
 85         dev_t dev;
 86 
 87         if (hwpoison_filter_dev_major == ~0U &&
 88             hwpoison_filter_dev_minor == ~0U)
 89                 return 0;
 90 
 91         /*
 92          * page_mapping() does not accept slab pages.
 93          */
 94         if (PageSlab(p))
 95                 return -EINVAL;
 96 
 97         mapping = page_mapping(p);
 98         if (mapping == NULL || mapping->host == NULL)
 99                 return -EINVAL;
100 
101         dev = mapping->host->i_sb->s_dev;
102         if (hwpoison_filter_dev_major != ~0U &&
103             hwpoison_filter_dev_major != MAJOR(dev))
104                 return -EINVAL;
105         if (hwpoison_filter_dev_minor != ~0U &&
106             hwpoison_filter_dev_minor != MINOR(dev))
107                 return -EINVAL;
108 
109         return 0;
110 }
111 
112 static int hwpoison_filter_flags(struct page *p)
113 {
114         if (!hwpoison_filter_flags_mask)
115                 return 0;
116 
117         if ((stable_page_flags(p) & hwpoison_filter_flags_mask) ==
118                                     hwpoison_filter_flags_value)
119                 return 0;
120         else
121                 return -EINVAL;
122 }
123 
124 /*
125  * This allows stress tests to limit test scope to a collection of tasks
126  * by putting them under some memcg. This prevents killing unrelated/important
127  * processes such as /sbin/init. Note that the target task may share clean
128  * pages with init (eg. libc text), which is harmless. If the target task
129  * share _dirty_ pages with another task B, the test scheme must make sure B
130  * is also included in the memcg. At last, due to race conditions this filter
131  * can only guarantee that the page either belongs to the memcg tasks, or is
132  * a freed page.
133  */
134 #ifdef CONFIG_MEMCG
135 u64 hwpoison_filter_memcg;
136 EXPORT_SYMBOL_GPL(hwpoison_filter_memcg);
137 static int hwpoison_filter_task(struct page *p)
138 {
139         if (!hwpoison_filter_memcg)
140                 return 0;
141 
142         if (page_cgroup_ino(p) != hwpoison_filter_memcg)
143                 return -EINVAL;
144 
145         return 0;
146 }
147 #else
148 static int hwpoison_filter_task(struct page *p) { return 0; }
149 #endif
150 
151 int hwpoison_filter(struct page *p)
152 {
153         if (!hwpoison_filter_enable)
154                 return 0;
155 
156         if (hwpoison_filter_dev(p))
157                 return -EINVAL;
158 
159         if (hwpoison_filter_flags(p))
160                 return -EINVAL;
161 
162         if (hwpoison_filter_task(p))
163                 return -EINVAL;
164 
165         return 0;
166 }
167 #else
168 int hwpoison_filter(struct page *p)
169 {
170         return 0;
171 }
172 #endif
173 
174 EXPORT_SYMBOL_GPL(hwpoison_filter);
175 
176 /*
177  * Send all the processes who have the page mapped a signal.
178  * ``action optional'' if they are not immediately affected by the error
179  * ``action required'' if error happened in current execution context
180  */
181 static int kill_proc(struct task_struct *t, unsigned long addr, int trapno,
182                         unsigned long pfn, struct page *page, int flags)
183 {
184         struct siginfo si;
185         int ret;
186 
187         pr_err("Memory failure: %#lx: Killing %s:%d due to hardware memory corruption\n",
188                 pfn, t->comm, t->pid);
189         si.si_signo = SIGBUS;
190         si.si_errno = 0;
191         si.si_addr = (void *)addr;
192 #ifdef __ARCH_SI_TRAPNO
193         si.si_trapno = trapno;
194 #endif
195         si.si_addr_lsb = compound_order(compound_head(page)) + PAGE_SHIFT;
196 
197         if ((flags & MF_ACTION_REQUIRED) && t->mm == current->mm) {
198                 si.si_code = BUS_MCEERR_AR;
199                 ret = force_sig_info(SIGBUS, &si, current);
200         } else {
201                 /*
202                  * Don't use force here, it's convenient if the signal
203                  * can be temporarily blocked.
204                  * This could cause a loop when the user sets SIGBUS
205                  * to SIG_IGN, but hopefully no one will do that?
206                  */
207                 si.si_code = BUS_MCEERR_AO;
208                 ret = send_sig_info(SIGBUS, &si, t);  /* synchronous? */
209         }
210         if (ret < 0)
211                 pr_info("Memory failure: Error sending signal to %s:%d: %d\n",
212                         t->comm, t->pid, ret);
213         return ret;
214 }
215 
216 /*
217  * When a unknown page type is encountered drain as many buffers as possible
218  * in the hope to turn the page into a LRU or free page, which we can handle.
219  */
220 void shake_page(struct page *p, int access)
221 {
222         if (!PageSlab(p)) {
223                 lru_add_drain_all();
224                 if (PageLRU(p))
225                         return;
226                 drain_all_pages(page_zone(p));
227                 if (PageLRU(p) || is_free_buddy_page(p))
228                         return;
229         }
230 
231         /*
232          * Only call shrink_node_slabs here (which would also shrink
233          * other caches) if access is not potentially fatal.
234          */
235         if (access)
236                 drop_slab_node(page_to_nid(p));
237 }
238 EXPORT_SYMBOL_GPL(shake_page);
239 
240 /*
241  * Kill all processes that have a poisoned page mapped and then isolate
242  * the page.
243  *
244  * General strategy:
245  * Find all processes having the page mapped and kill them.
246  * But we keep a page reference around so that the page is not
247  * actually freed yet.
248  * Then stash the page away
249  *
250  * There's no convenient way to get back to mapped processes
251  * from the VMAs. So do a brute-force search over all
252  * running processes.
253  *
254  * Remember that machine checks are not common (or rather
255  * if they are common you have other problems), so this shouldn't
256  * be a performance issue.
257  *
258  * Also there are some races possible while we get from the
259  * error detection to actually handle it.
260  */
261 
262 struct to_kill {
263         struct list_head nd;
264         struct task_struct *tsk;
265         unsigned long addr;
266         char addr_valid;
267 };
268 
269 /*
270  * Failure handling: if we can't find or can't kill a process there's
271  * not much we can do.  We just print a message and ignore otherwise.
272  */
273 
274 /*
275  * Schedule a process for later kill.
276  * Uses GFP_ATOMIC allocations to avoid potential recursions in the VM.
277  * TBD would GFP_NOIO be enough?
278  */
279 static void add_to_kill(struct task_struct *tsk, struct page *p,
280                        struct vm_area_struct *vma,
281                        struct list_head *to_kill,
282                        struct to_kill **tkc)
283 {
284         struct to_kill *tk;
285 
286         if (*tkc) {
287                 tk = *tkc;
288                 *tkc = NULL;
289         } else {
290                 tk = kmalloc(sizeof(struct to_kill), GFP_ATOMIC);
291                 if (!tk) {
292                         pr_err("Memory failure: Out of memory while machine check handling\n");
293                         return;
294                 }
295         }
296         tk->addr = page_address_in_vma(p, vma);
297         tk->addr_valid = 1;
298 
299         /*
300          * In theory we don't have to kill when the page was
301          * munmaped. But it could be also a mremap. Since that's
302          * likely very rare kill anyways just out of paranoia, but use
303          * a SIGKILL because the error is not contained anymore.
304          */
305         if (tk->addr == -EFAULT) {
306                 pr_info("Memory failure: Unable to find user space address %lx in %s\n",
307                         page_to_pfn(p), tsk->comm);
308                 tk->addr_valid = 0;
309         }
310         get_task_struct(tsk);
311         tk->tsk = tsk;
312         list_add_tail(&tk->nd, to_kill);
313 }
314 
315 /*
316  * Kill the processes that have been collected earlier.
317  *
318  * Only do anything when DOIT is set, otherwise just free the list
319  * (this is used for clean pages which do not need killing)
320  * Also when FAIL is set do a force kill because something went
321  * wrong earlier.
322  */
323 static void kill_procs(struct list_head *to_kill, int forcekill, int trapno,
324                           int fail, struct page *page, unsigned long pfn,
325                           int flags)
326 {
327         struct to_kill *tk, *next;
328 
329         list_for_each_entry_safe (tk, next, to_kill, nd) {
330                 if (forcekill) {
331                         /*
332                          * In case something went wrong with munmapping
333                          * make sure the process doesn't catch the
334                          * signal and then access the memory. Just kill it.
335                          */
336                         if (fail || tk->addr_valid == 0) {
337                                 pr_err("Memory failure: %#lx: forcibly killing %s:%d because of failure to unmap corrupted page\n",
338                                        pfn, tk->tsk->comm, tk->tsk->pid);
339                                 force_sig(SIGKILL, tk->tsk);
340                         }
341 
342                         /*
343                          * In theory the process could have mapped
344                          * something else on the address in-between. We could
345                          * check for that, but we need to tell the
346                          * process anyways.
347                          */
348                         else if (kill_proc(tk->tsk, tk->addr, trapno,
349                                               pfn, page, flags) < 0)
350                                 pr_err("Memory failure: %#lx: Cannot send advisory machine check signal to %s:%d\n",
351                                        pfn, tk->tsk->comm, tk->tsk->pid);
352                 }
353                 put_task_struct(tk->tsk);
354                 kfree(tk);
355         }
356 }
357 
358 /*
359  * Find a dedicated thread which is supposed to handle SIGBUS(BUS_MCEERR_AO)
360  * on behalf of the thread group. Return task_struct of the (first found)
361  * dedicated thread if found, and return NULL otherwise.
362  *
363  * We already hold read_lock(&tasklist_lock) in the caller, so we don't
364  * have to call rcu_read_lock/unlock() in this function.
365  */
366 static struct task_struct *find_early_kill_thread(struct task_struct *tsk)
367 {
368         struct task_struct *t;
369 
370         for_each_thread(tsk, t)
371                 if ((t->flags & PF_MCE_PROCESS) && (t->flags & PF_MCE_EARLY))
372                         return t;
373         return NULL;
374 }
375 
376 /*
377  * Determine whether a given process is "early kill" process which expects
378  * to be signaled when some page under the process is hwpoisoned.
379  * Return task_struct of the dedicated thread (main thread unless explicitly
380  * specified) if the process is "early kill," and otherwise returns NULL.
381  */
382 static struct task_struct *task_early_kill(struct task_struct *tsk,
383                                            int force_early)
384 {
385         struct task_struct *t;
386         if (!tsk->mm)
387                 return NULL;
388         if (force_early)
389                 return tsk;
390         t = find_early_kill_thread(tsk);
391         if (t)
392                 return t;
393         if (sysctl_memory_failure_early_kill)
394                 return tsk;
395         return NULL;
396 }
397 
398 /*
399  * Collect processes when the error hit an anonymous page.
400  */
401 static void collect_procs_anon(struct page *page, struct list_head *to_kill,
402                               struct to_kill **tkc, int force_early)
403 {
404         struct vm_area_struct *vma;
405         struct task_struct *tsk;
406         struct anon_vma *av;
407         pgoff_t pgoff;
408 
409         av = page_lock_anon_vma_read(page);
410         if (av == NULL) /* Not actually mapped anymore */
411                 return;
412 
413         pgoff = page_to_pgoff(page);
414         read_lock(&tasklist_lock);
415         for_each_process (tsk) {
416                 struct anon_vma_chain *vmac;
417                 struct task_struct *t = task_early_kill(tsk, force_early);
418 
419                 if (!t)
420                         continue;
421                 anon_vma_interval_tree_foreach(vmac, &av->rb_root,
422                                                pgoff, pgoff) {
423                         vma = vmac->vma;
424                         if (!page_mapped_in_vma(page, vma))
425                                 continue;
426                         if (vma->vm_mm == t->mm)
427                                 add_to_kill(t, page, vma, to_kill, tkc);
428                 }
429         }
430         read_unlock(&tasklist_lock);
431         page_unlock_anon_vma_read(av);
432 }
433 
434 /*
435  * Collect processes when the error hit a file mapped page.
436  */
437 static void collect_procs_file(struct page *page, struct list_head *to_kill,
438                               struct to_kill **tkc, int force_early)
439 {
440         struct vm_area_struct *vma;
441         struct task_struct *tsk;
442         struct address_space *mapping = page->mapping;
443 
444         i_mmap_lock_read(mapping);
445         read_lock(&tasklist_lock);
446         for_each_process(tsk) {
447                 pgoff_t pgoff = page_to_pgoff(page);
448                 struct task_struct *t = task_early_kill(tsk, force_early);
449 
450                 if (!t)
451                         continue;
452                 vma_interval_tree_foreach(vma, &mapping->i_mmap, pgoff,
453                                       pgoff) {
454                         /*
455                          * Send early kill signal to tasks where a vma covers
456                          * the page but the corrupted page is not necessarily
457                          * mapped it in its pte.
458                          * Assume applications who requested early kill want
459                          * to be informed of all such data corruptions.
460                          */
461                         if (vma->vm_mm == t->mm)
462                                 add_to_kill(t, page, vma, to_kill, tkc);
463                 }
464         }
465         read_unlock(&tasklist_lock);
466         i_mmap_unlock_read(mapping);
467 }
468 
469 /*
470  * Collect the processes who have the corrupted page mapped to kill.
471  * This is done in two steps for locking reasons.
472  * First preallocate one tokill structure outside the spin locks,
473  * so that we can kill at least one process reasonably reliable.
474  */
475 static void collect_procs(struct page *page, struct list_head *tokill,
476                                 int force_early)
477 {
478         struct to_kill *tk;
479 
480         if (!page->mapping)
481                 return;
482 
483         tk = kmalloc(sizeof(struct to_kill), GFP_NOIO);
484         if (!tk)
485                 return;
486         if (PageAnon(page))
487                 collect_procs_anon(page, tokill, &tk, force_early);
488         else
489                 collect_procs_file(page, tokill, &tk, force_early);
490         kfree(tk);
491 }
492 
493 static const char *action_name[] = {
494         [MF_IGNORED] = "Ignored",
495         [MF_FAILED] = "Failed",
496         [MF_DELAYED] = "Delayed",
497         [MF_RECOVERED] = "Recovered",
498 };
499 
500 static const char * const action_page_types[] = {
501         [MF_MSG_KERNEL]                 = "reserved kernel page",
502         [MF_MSG_KERNEL_HIGH_ORDER]      = "high-order kernel page",
503         [MF_MSG_SLAB]                   = "kernel slab page",
504         [MF_MSG_DIFFERENT_COMPOUND]     = "different compound page after locking",
505         [MF_MSG_POISONED_HUGE]          = "huge page already hardware poisoned",
506         [MF_MSG_HUGE]                   = "huge page",
507         [MF_MSG_FREE_HUGE]              = "free huge page",
508         [MF_MSG_UNMAP_FAILED]           = "unmapping failed page",
509         [MF_MSG_DIRTY_SWAPCACHE]        = "dirty swapcache page",
510         [MF_MSG_CLEAN_SWAPCACHE]        = "clean swapcache page",
511         [MF_MSG_DIRTY_MLOCKED_LRU]      = "dirty mlocked LRU page",
512         [MF_MSG_CLEAN_MLOCKED_LRU]      = "clean mlocked LRU page",
513         [MF_MSG_DIRTY_UNEVICTABLE_LRU]  = "dirty unevictable LRU page",
514         [MF_MSG_CLEAN_UNEVICTABLE_LRU]  = "clean unevictable LRU page",
515         [MF_MSG_DIRTY_LRU]              = "dirty LRU page",
516         [MF_MSG_CLEAN_LRU]              = "clean LRU page",
517         [MF_MSG_TRUNCATED_LRU]          = "already truncated LRU page",
518         [MF_MSG_BUDDY]                  = "free buddy page",
519         [MF_MSG_BUDDY_2ND]              = "free buddy page (2nd try)",
520         [MF_MSG_UNKNOWN]                = "unknown page",
521 };
522 
523 /*
524  * XXX: It is possible that a page is isolated from LRU cache,
525  * and then kept in swap cache or failed to remove from page cache.
526  * The page count will stop it from being freed by unpoison.
527  * Stress tests should be aware of this memory leak problem.
528  */
529 static int delete_from_lru_cache(struct page *p)
530 {
531         if (!isolate_lru_page(p)) {
532                 /*
533                  * Clear sensible page flags, so that the buddy system won't
534                  * complain when the page is unpoison-and-freed.
535                  */
536                 ClearPageActive(p);
537                 ClearPageUnevictable(p);
538                 /*
539                  * drop the page count elevated by isolate_lru_page()
540                  */
541                 put_page(p);
542                 return 0;
543         }
544         return -EIO;
545 }
546 
547 /*
548  * Error hit kernel page.
549  * Do nothing, try to be lucky and not touch this instead. For a few cases we
550  * could be more sophisticated.
551  */
552 static int me_kernel(struct page *p, unsigned long pfn)
553 {
554         return MF_IGNORED;
555 }
556 
557 /*
558  * Page in unknown state. Do nothing.
559  */
560 static int me_unknown(struct page *p, unsigned long pfn)
561 {
562         pr_err("Memory failure: %#lx: Unknown page state\n", pfn);
563         return MF_FAILED;
564 }
565 
566 /*
567  * Clean (or cleaned) page cache page.
568  */
569 static int me_pagecache_clean(struct page *p, unsigned long pfn)
570 {
571         int err;
572         int ret = MF_FAILED;
573         struct address_space *mapping;
574 
575         delete_from_lru_cache(p);
576 
577         /*
578          * For anonymous pages we're done the only reference left
579          * should be the one m_f() holds.
580          */
581         if (PageAnon(p))
582                 return MF_RECOVERED;
583 
584         /*
585          * Now truncate the page in the page cache. This is really
586          * more like a "temporary hole punch"
587          * Don't do this for block devices when someone else
588          * has a reference, because it could be file system metadata
589          * and that's not safe to truncate.
590          */
591         mapping = page_mapping(p);
592         if (!mapping) {
593                 /*
594                  * Page has been teared down in the meanwhile
595                  */
596                 return MF_FAILED;
597         }
598 
599         /*
600          * Truncation is a bit tricky. Enable it per file system for now.
601          *
602          * Open: to take i_mutex or not for this? Right now we don't.
603          */
604         if (mapping->a_ops->error_remove_page) {
605                 err = mapping->a_ops->error_remove_page(mapping, p);
606                 if (err != 0) {
607                         pr_info("Memory failure: %#lx: Failed to punch page: %d\n",
608                                 pfn, err);
609                 } else if (page_has_private(p) &&
610                                 !try_to_release_page(p, GFP_NOIO)) {
611                         pr_info("Memory failure: %#lx: failed to release buffers\n",
612                                 pfn);
613                 } else {
614                         ret = MF_RECOVERED;
615                 }
616         } else {
617                 /*
618                  * If the file system doesn't support it just invalidate
619                  * This fails on dirty or anything with private pages
620                  */
621                 if (invalidate_inode_page(p))
622                         ret = MF_RECOVERED;
623                 else
624                         pr_info("Memory failure: %#lx: Failed to invalidate\n",
625                                 pfn);
626         }
627         return ret;
628 }
629 
630 /*
631  * Dirty pagecache page
632  * Issues: when the error hit a hole page the error is not properly
633  * propagated.
634  */
635 static int me_pagecache_dirty(struct page *p, unsigned long pfn)
636 {
637         struct address_space *mapping = page_mapping(p);
638 
639         SetPageError(p);
640         /* TBD: print more information about the file. */
641         if (mapping) {
642                 /*
643                  * IO error will be reported by write(), fsync(), etc.
644                  * who check the mapping.
645                  * This way the application knows that something went
646                  * wrong with its dirty file data.
647                  *
648                  * There's one open issue:
649                  *
650                  * The EIO will be only reported on the next IO
651                  * operation and then cleared through the IO map.
652                  * Normally Linux has two mechanisms to pass IO error
653                  * first through the AS_EIO flag in the address space
654                  * and then through the PageError flag in the page.
655                  * Since we drop pages on memory failure handling the
656                  * only mechanism open to use is through AS_AIO.
657                  *
658                  * This has the disadvantage that it gets cleared on
659                  * the first operation that returns an error, while
660                  * the PageError bit is more sticky and only cleared
661                  * when the page is reread or dropped.  If an
662                  * application assumes it will always get error on
663                  * fsync, but does other operations on the fd before
664                  * and the page is dropped between then the error
665                  * will not be properly reported.
666                  *
667                  * This can already happen even without hwpoisoned
668                  * pages: first on metadata IO errors (which only
669                  * report through AS_EIO) or when the page is dropped
670                  * at the wrong time.
671                  *
672                  * So right now we assume that the application DTRT on
673                  * the first EIO, but we're not worse than other parts
674                  * of the kernel.
675                  */
676                 mapping_set_error(mapping, EIO);
677         }
678 
679         return me_pagecache_clean(p, pfn);
680 }
681 
682 /*
683  * Clean and dirty swap cache.
684  *
685  * Dirty swap cache page is tricky to handle. The page could live both in page
686  * cache and swap cache(ie. page is freshly swapped in). So it could be
687  * referenced concurrently by 2 types of PTEs:
688  * normal PTEs and swap PTEs. We try to handle them consistently by calling
689  * try_to_unmap(TTU_IGNORE_HWPOISON) to convert the normal PTEs to swap PTEs,
690  * and then
691  *      - clear dirty bit to prevent IO
692  *      - remove from LRU
693  *      - but keep in the swap cache, so that when we return to it on
694  *        a later page fault, we know the application is accessing
695  *        corrupted data and shall be killed (we installed simple
696  *        interception code in do_swap_page to catch it).
697  *
698  * Clean swap cache pages can be directly isolated. A later page fault will
699  * bring in the known good data from disk.
700  */
701 static int me_swapcache_dirty(struct page *p, unsigned long pfn)
702 {
703         ClearPageDirty(p);
704         /* Trigger EIO in shmem: */
705         ClearPageUptodate(p);
706 
707         if (!delete_from_lru_cache(p))
708                 return MF_DELAYED;
709         else
710                 return MF_FAILED;
711 }
712 
713 static int me_swapcache_clean(struct page *p, unsigned long pfn)
714 {
715         delete_from_swap_cache(p);
716 
717         if (!delete_from_lru_cache(p))
718                 return MF_RECOVERED;
719         else
720                 return MF_FAILED;
721 }
722 
723 /*
724  * Huge pages. Needs work.
725  * Issues:
726  * - Error on hugepage is contained in hugepage unit (not in raw page unit.)
727  *   To narrow down kill region to one page, we need to break up pmd.
728  */
729 static int me_huge_page(struct page *p, unsigned long pfn)
730 {
731         int res = 0;
732         struct page *hpage = compound_head(p);
733 
734         if (!PageHuge(hpage))
735                 return MF_DELAYED;
736 
737         /*
738          * We can safely recover from error on free or reserved (i.e.
739          * not in-use) hugepage by dequeuing it from freelist.
740          * To check whether a hugepage is in-use or not, we can't use
741          * page->lru because it can be used in other hugepage operations,
742          * such as __unmap_hugepage_range() and gather_surplus_pages().
743          * So instead we use page_mapping() and PageAnon().
744          */
745         if (!(page_mapping(hpage) || PageAnon(hpage))) {
746                 res = dequeue_hwpoisoned_huge_page(hpage);
747                 if (!res)
748                         return MF_RECOVERED;
749         }
750         return MF_DELAYED;
751 }
752 
753 /*
754  * Various page states we can handle.
755  *
756  * A page state is defined by its current page->flags bits.
757  * The table matches them in order and calls the right handler.
758  *
759  * This is quite tricky because we can access page at any time
760  * in its live cycle, so all accesses have to be extremely careful.
761  *
762  * This is not complete. More states could be added.
763  * For any missing state don't attempt recovery.
764  */
765 
766 #define dirty           (1UL << PG_dirty)
767 #define sc              ((1UL << PG_swapcache) | (1UL << PG_swapbacked))
768 #define unevict         (1UL << PG_unevictable)
769 #define mlock           (1UL << PG_mlocked)
770 #define writeback       (1UL << PG_writeback)
771 #define lru             (1UL << PG_lru)
772 #define head            (1UL << PG_head)
773 #define slab            (1UL << PG_slab)
774 #define reserved        (1UL << PG_reserved)
775 
776 static struct page_state {
777         unsigned long mask;
778         unsigned long res;
779         enum mf_action_page_type type;
780         int (*action)(struct page *p, unsigned long pfn);
781 } error_states[] = {
782         { reserved,     reserved,       MF_MSG_KERNEL,  me_kernel },
783         /*
784          * free pages are specially detected outside this table:
785          * PG_buddy pages only make a small fraction of all free pages.
786          */
787 
788         /*
789          * Could in theory check if slab page is free or if we can drop
790          * currently unused objects without touching them. But just
791          * treat it as standard kernel for now.
792          */
793         { slab,         slab,           MF_MSG_SLAB,    me_kernel },
794 
795         { head,         head,           MF_MSG_HUGE,            me_huge_page },
796 
797         { sc|dirty,     sc|dirty,       MF_MSG_DIRTY_SWAPCACHE, me_swapcache_dirty },
798         { sc|dirty,     sc,             MF_MSG_CLEAN_SWAPCACHE, me_swapcache_clean },
799 
800         { mlock|dirty,  mlock|dirty,    MF_MSG_DIRTY_MLOCKED_LRU,       me_pagecache_dirty },
801         { mlock|dirty,  mlock,          MF_MSG_CLEAN_MLOCKED_LRU,       me_pagecache_clean },
802 
803         { unevict|dirty, unevict|dirty, MF_MSG_DIRTY_UNEVICTABLE_LRU,   me_pagecache_dirty },
804         { unevict|dirty, unevict,       MF_MSG_CLEAN_UNEVICTABLE_LRU,   me_pagecache_clean },
805 
806         { lru|dirty,    lru|dirty,      MF_MSG_DIRTY_LRU,       me_pagecache_dirty },
807         { lru|dirty,    lru,            MF_MSG_CLEAN_LRU,       me_pagecache_clean },
808 
809         /*
810          * Catchall entry: must be at end.
811          */
812         { 0,            0,              MF_MSG_UNKNOWN, me_unknown },
813 };
814 
815 #undef dirty
816 #undef sc
817 #undef unevict
818 #undef mlock
819 #undef writeback
820 #undef lru
821 #undef head
822 #undef slab
823 #undef reserved
824 
825 /*
826  * "Dirty/Clean" indication is not 100% accurate due to the possibility of
827  * setting PG_dirty outside page lock. See also comment above set_page_dirty().
828  */
829 static void action_result(unsigned long pfn, enum mf_action_page_type type,
830                           enum mf_result result)
831 {
832         trace_memory_failure_event(pfn, type, result);
833 
834         pr_err("Memory failure: %#lx: recovery action for %s: %s\n",
835                 pfn, action_page_types[type], action_name[result]);
836 }
837 
838 static int page_action(struct page_state *ps, struct page *p,
839                         unsigned long pfn)
840 {
841         int result;
842         int count;
843 
844         result = ps->action(p, pfn);
845 
846         count = page_count(p) - 1;
847         if (ps->action == me_swapcache_dirty && result == MF_DELAYED)
848                 count--;
849         if (count != 0) {
850                 pr_err("Memory failure: %#lx: %s still referenced by %d users\n",
851                        pfn, action_page_types[ps->type], count);
852                 result = MF_FAILED;
853         }
854         action_result(pfn, ps->type, result);
855 
856         /* Could do more checks here if page looks ok */
857         /*
858          * Could adjust zone counters here to correct for the missing page.
859          */
860 
861         return (result == MF_RECOVERED || result == MF_DELAYED) ? 0 : -EBUSY;
862 }
863 
864 /**
865  * get_hwpoison_page() - Get refcount for memory error handling:
866  * @page:       raw error page (hit by memory error)
867  *
868  * Return: return 0 if failed to grab the refcount, otherwise true (some
869  * non-zero value.)
870  */
871 int get_hwpoison_page(struct page *page)
872 {
873         struct page *head = compound_head(page);
874 
875         if (!PageHuge(head) && PageTransHuge(head)) {
876                 /*
877                  * Non anonymous thp exists only in allocation/free time. We
878                  * can't handle such a case correctly, so let's give it up.
879                  * This should be better than triggering BUG_ON when kernel
880                  * tries to touch the "partially handled" page.
881                  */
882                 if (!PageAnon(head)) {
883                         pr_err("Memory failure: %#lx: non anonymous thp\n",
884                                 page_to_pfn(page));
885                         return 0;
886                 }
887         }
888 
889         if (get_page_unless_zero(head)) {
890                 if (head == compound_head(page))
891                         return 1;
892 
893                 pr_info("Memory failure: %#lx cannot catch tail\n",
894                         page_to_pfn(page));
895                 put_page(head);
896         }
897 
898         return 0;
899 }
900 EXPORT_SYMBOL_GPL(get_hwpoison_page);
901 
902 /*
903  * Do all that is necessary to remove user space mappings. Unmap
904  * the pages and send SIGBUS to the processes if the data was dirty.
905  */
906 static int hwpoison_user_mappings(struct page *p, unsigned long pfn,
907                                   int trapno, int flags, struct page **hpagep)
908 {
909         enum ttu_flags ttu = TTU_UNMAP | TTU_IGNORE_MLOCK | TTU_IGNORE_ACCESS;
910         struct address_space *mapping;
911         LIST_HEAD(tokill);
912         int ret;
913         int kill = 1, forcekill;
914         struct page *hpage = *hpagep;
915 
916         /*
917          * Here we are interested only in user-mapped pages, so skip any
918          * other types of pages.
919          */
920         if (PageReserved(p) || PageSlab(p))
921                 return SWAP_SUCCESS;
922         if (!(PageLRU(hpage) || PageHuge(p)))
923                 return SWAP_SUCCESS;
924 
925         /*
926          * This check implies we don't kill processes if their pages
927          * are in the swap cache early. Those are always late kills.
928          */
929         if (!page_mapped(hpage))
930                 return SWAP_SUCCESS;
931 
932         if (PageKsm(p)) {
933                 pr_err("Memory failure: %#lx: can't handle KSM pages.\n", pfn);
934                 return SWAP_FAIL;
935         }
936 
937         if (PageSwapCache(p)) {
938                 pr_err("Memory failure: %#lx: keeping poisoned page in swap cache\n",
939                         pfn);
940                 ttu |= TTU_IGNORE_HWPOISON;
941         }
942 
943         /*
944          * Propagate the dirty bit from PTEs to struct page first, because we
945          * need this to decide if we should kill or just drop the page.
946          * XXX: the dirty test could be racy: set_page_dirty() may not always
947          * be called inside page lock (it's recommended but not enforced).
948          */
949         mapping = page_mapping(hpage);
950         if (!(flags & MF_MUST_KILL) && !PageDirty(hpage) && mapping &&
951             mapping_cap_writeback_dirty(mapping)) {
952                 if (page_mkclean(hpage)) {
953                         SetPageDirty(hpage);
954                 } else {
955                         kill = 0;
956                         ttu |= TTU_IGNORE_HWPOISON;
957                         pr_info("Memory failure: %#lx: corrupted page was clean: dropped without side effects\n",
958                                 pfn);
959                 }
960         }
961 
962         /*
963          * First collect all the processes that have the page
964          * mapped in dirty form.  This has to be done before try_to_unmap,
965          * because ttu takes the rmap data structures down.
966          *
967          * Error handling: We ignore errors here because
968          * there's nothing that can be done.
969          */
970         if (kill)
971                 collect_procs(hpage, &tokill, flags & MF_ACTION_REQUIRED);
972 
973         ret = try_to_unmap(hpage, ttu);
974         if (ret != SWAP_SUCCESS)
975                 pr_err("Memory failure: %#lx: failed to unmap page (mapcount=%d)\n",
976                        pfn, page_mapcount(hpage));
977 
978         /*
979          * Now that the dirty bit has been propagated to the
980          * struct page and all unmaps done we can decide if
981          * killing is needed or not.  Only kill when the page
982          * was dirty or the process is not restartable,
983          * otherwise the tokill list is merely
984          * freed.  When there was a problem unmapping earlier
985          * use a more force-full uncatchable kill to prevent
986          * any accesses to the poisoned memory.
987          */
988         forcekill = PageDirty(hpage) || (flags & MF_MUST_KILL);
989         kill_procs(&tokill, forcekill, trapno,
990                       ret != SWAP_SUCCESS, p, pfn, flags);
991 
992         return ret;
993 }
994 
995 static void set_page_hwpoison_huge_page(struct page *hpage)
996 {
997         int i;
998         int nr_pages = 1 << compound_order(hpage);
999         for (i = 0; i < nr_pages; i++)
1000                 SetPageHWPoison(hpage + i);
1001 }
1002 
1003 static void clear_page_hwpoison_huge_page(struct page *hpage)
1004 {
1005         int i;
1006         int nr_pages = 1 << compound_order(hpage);
1007         for (i = 0; i < nr_pages; i++)
1008                 ClearPageHWPoison(hpage + i);
1009 }
1010 
1011 /**
1012  * memory_failure - Handle memory failure of a page.
1013  * @pfn: Page Number of the corrupted page
1014  * @trapno: Trap number reported in the signal to user space.
1015  * @flags: fine tune action taken
1016  *
1017  * This function is called by the low level machine check code
1018  * of an architecture when it detects hardware memory corruption
1019  * of a page. It tries its best to recover, which includes
1020  * dropping pages, killing processes etc.
1021  *
1022  * The function is primarily of use for corruptions that
1023  * happen outside the current execution context (e.g. when
1024  * detected by a background scrubber)
1025  *
1026  * Must run in process context (e.g. a work queue) with interrupts
1027  * enabled and no spinlocks hold.
1028  */
1029 int memory_failure(unsigned long pfn, int trapno, int flags)
1030 {
1031         struct page_state *ps;
1032         struct page *p;
1033         struct page *hpage;
1034         struct page *orig_head;
1035         int res;
1036         unsigned int nr_pages;
1037         unsigned long page_flags;
1038 
1039         if (!sysctl_memory_failure_recovery)
1040                 panic("Memory failure from trap %d on page %lx", trapno, pfn);
1041 
1042         if (!pfn_valid(pfn)) {
1043                 pr_err("Memory failure: %#lx: memory outside kernel control\n",
1044                         pfn);
1045                 return -ENXIO;
1046         }
1047 
1048         p = pfn_to_page(pfn);
1049         orig_head = hpage = compound_head(p);
1050         if (TestSetPageHWPoison(p)) {
1051                 pr_err("Memory failure: %#lx: already hardware poisoned\n",
1052                         pfn);
1053                 return 0;
1054         }
1055 
1056         /*
1057          * Currently errors on hugetlbfs pages are measured in hugepage units,
1058          * so nr_pages should be 1 << compound_order.  OTOH when errors are on
1059          * transparent hugepages, they are supposed to be split and error
1060          * measurement is done in normal page units.  So nr_pages should be one
1061          * in this case.
1062          */
1063         if (PageHuge(p))
1064                 nr_pages = 1 << compound_order(hpage);
1065         else /* normal page or thp */
1066                 nr_pages = 1;
1067         num_poisoned_pages_add(nr_pages);
1068 
1069         /*
1070          * We need/can do nothing about count=0 pages.
1071          * 1) it's a free page, and therefore in safe hand:
1072          *    prep_new_page() will be the gate keeper.
1073          * 2) it's a free hugepage, which is also safe:
1074          *    an affected hugepage will be dequeued from hugepage freelist,
1075          *    so there's no concern about reusing it ever after.
1076          * 3) it's part of a non-compound high order page.
1077          *    Implies some kernel user: cannot stop them from
1078          *    R/W the page; let's pray that the page has been
1079          *    used and will be freed some time later.
1080          * In fact it's dangerous to directly bump up page count from 0,
1081          * that may make page_freeze_refs()/page_unfreeze_refs() mismatch.
1082          */
1083         if (!(flags & MF_COUNT_INCREASED) && !get_hwpoison_page(p)) {
1084                 if (is_free_buddy_page(p)) {
1085                         action_result(pfn, MF_MSG_BUDDY, MF_DELAYED);
1086                         return 0;
1087                 } else if (PageHuge(hpage)) {
1088                         /*
1089                          * Check "filter hit" and "race with other subpage."
1090                          */
1091                         lock_page(hpage);
1092                         if (PageHWPoison(hpage)) {
1093                                 if ((hwpoison_filter(p) && TestClearPageHWPoison(p))
1094                                     || (p != hpage && TestSetPageHWPoison(hpage))) {
1095                                         num_poisoned_pages_sub(nr_pages);
1096                                         unlock_page(hpage);
1097                                         return 0;
1098                                 }
1099                         }
1100                         set_page_hwpoison_huge_page(hpage);
1101                         res = dequeue_hwpoisoned_huge_page(hpage);
1102                         action_result(pfn, MF_MSG_FREE_HUGE,
1103                                       res ? MF_IGNORED : MF_DELAYED);
1104                         unlock_page(hpage);
1105                         return res;
1106                 } else {
1107                         action_result(pfn, MF_MSG_KERNEL_HIGH_ORDER, MF_IGNORED);
1108                         return -EBUSY;
1109                 }
1110         }
1111 
1112         if (!PageHuge(p) && PageTransHuge(hpage)) {
1113                 lock_page(p);
1114                 if (!PageAnon(p) || unlikely(split_huge_page(p))) {
1115                         unlock_page(p);
1116                         if (!PageAnon(p))
1117                                 pr_err("Memory failure: %#lx: non anonymous thp\n",
1118                                         pfn);
1119                         else
1120                                 pr_err("Memory failure: %#lx: thp split failed\n",
1121                                         pfn);
1122                         if (TestClearPageHWPoison(p))
1123                                 num_poisoned_pages_sub(nr_pages);
1124                         put_hwpoison_page(p);
1125                         return -EBUSY;
1126                 }
1127                 unlock_page(p);
1128                 VM_BUG_ON_PAGE(!page_count(p), p);
1129                 hpage = compound_head(p);
1130         }
1131 
1132         /*
1133          * We ignore non-LRU pages for good reasons.
1134          * - PG_locked is only well defined for LRU pages and a few others
1135          * - to avoid races with __SetPageLocked()
1136          * - to avoid races with __SetPageSlab*() (and more non-atomic ops)
1137          * The check (unnecessarily) ignores LRU pages being isolated and
1138          * walked by the page reclaim code, however that's not a big loss.
1139          */
1140         if (!PageHuge(p)) {
1141                 if (!PageLRU(p))
1142                         shake_page(p, 0);
1143                 if (!PageLRU(p)) {
1144                         /*
1145                          * shake_page could have turned it free.
1146                          */
1147                         if (is_free_buddy_page(p)) {
1148                                 if (flags & MF_COUNT_INCREASED)
1149                                         action_result(pfn, MF_MSG_BUDDY, MF_DELAYED);
1150                                 else
1151                                         action_result(pfn, MF_MSG_BUDDY_2ND,
1152                                                       MF_DELAYED);
1153                                 return 0;
1154                         }
1155                 }
1156         }
1157 
1158         lock_page(hpage);
1159 
1160         /*
1161          * The page could have changed compound pages during the locking.
1162          * If this happens just bail out.
1163          */
1164         if (PageCompound(p) && compound_head(p) != orig_head) {
1165                 action_result(pfn, MF_MSG_DIFFERENT_COMPOUND, MF_IGNORED);
1166                 res = -EBUSY;
1167                 goto out;
1168         }
1169 
1170         /*
1171          * We use page flags to determine what action should be taken, but
1172          * the flags can be modified by the error containment action.  One
1173          * example is an mlocked page, where PG_mlocked is cleared by
1174          * page_remove_rmap() in try_to_unmap_one(). So to determine page status
1175          * correctly, we save a copy of the page flags at this time.
1176          */
1177         page_flags = p->flags;
1178 
1179         /*
1180          * unpoison always clear PG_hwpoison inside page lock
1181          */
1182         if (!PageHWPoison(p)) {
1183                 pr_err("Memory failure: %#lx: just unpoisoned\n", pfn);
1184                 num_poisoned_pages_sub(nr_pages);
1185                 unlock_page(hpage);
1186                 put_hwpoison_page(hpage);
1187                 return 0;
1188         }
1189         if (hwpoison_filter(p)) {
1190                 if (TestClearPageHWPoison(p))
1191                         num_poisoned_pages_sub(nr_pages);
1192                 unlock_page(hpage);
1193                 put_hwpoison_page(hpage);
1194                 return 0;
1195         }
1196 
1197         if (!PageHuge(p) && !PageTransTail(p) && !PageLRU(p))
1198                 goto identify_page_state;
1199 
1200         /*
1201          * For error on the tail page, we should set PG_hwpoison
1202          * on the head page to show that the hugepage is hwpoisoned
1203          */
1204         if (PageHuge(p) && PageTail(p) && TestSetPageHWPoison(hpage)) {
1205                 action_result(pfn, MF_MSG_POISONED_HUGE, MF_IGNORED);
1206                 unlock_page(hpage);
1207                 put_hwpoison_page(hpage);
1208                 return 0;
1209         }
1210         /*
1211          * Set PG_hwpoison on all pages in an error hugepage,
1212          * because containment is done in hugepage unit for now.
1213          * Since we have done TestSetPageHWPoison() for the head page with
1214          * page lock held, we can safely set PG_hwpoison bits on tail pages.
1215          */
1216         if (PageHuge(p))
1217                 set_page_hwpoison_huge_page(hpage);
1218 
1219         /*
1220          * It's very difficult to mess with pages currently under IO
1221          * and in many cases impossible, so we just avoid it here.
1222          */
1223         wait_on_page_writeback(p);
1224 
1225         /*
1226          * Now take care of user space mappings.
1227          * Abort on fail: __delete_from_page_cache() assumes unmapped page.
1228          *
1229          * When the raw error page is thp tail page, hpage points to the raw
1230          * page after thp split.
1231          */
1232         if (hwpoison_user_mappings(p, pfn, trapno, flags, &hpage)
1233             != SWAP_SUCCESS) {
1234                 action_result(pfn, MF_MSG_UNMAP_FAILED, MF_IGNORED);
1235                 res = -EBUSY;
1236                 goto out;
1237         }
1238 
1239         /*
1240          * Torn down by someone else?
1241          */
1242         if (PageLRU(p) && !PageSwapCache(p) && p->mapping == NULL) {
1243                 action_result(pfn, MF_MSG_TRUNCATED_LRU, MF_IGNORED);
1244                 res = -EBUSY;
1245                 goto out;
1246         }
1247 
1248 identify_page_state:
1249         res = -EBUSY;
1250         /*
1251          * The first check uses the current page flags which may not have any
1252          * relevant information. The second check with the saved page flagss is
1253          * carried out only if the first check can't determine the page status.
1254          */
1255         for (ps = error_states;; ps++)
1256                 if ((p->flags & ps->mask) == ps->res)
1257                         break;
1258 
1259         page_flags |= (p->flags & (1UL << PG_dirty));
1260 
1261         if (!ps->mask)
1262                 for (ps = error_states;; ps++)
1263                         if ((page_flags & ps->mask) == ps->res)
1264                                 break;
1265         res = page_action(ps, p, pfn);
1266 out:
1267         unlock_page(hpage);
1268         return res;
1269 }
1270 EXPORT_SYMBOL_GPL(memory_failure);
1271 
1272 #define MEMORY_FAILURE_FIFO_ORDER       4
1273 #define MEMORY_FAILURE_FIFO_SIZE        (1 << MEMORY_FAILURE_FIFO_ORDER)
1274 
1275 struct memory_failure_entry {
1276         unsigned long pfn;
1277         int trapno;
1278         int flags;
1279 };
1280 
1281 struct memory_failure_cpu {
1282         DECLARE_KFIFO(fifo, struct memory_failure_entry,
1283                       MEMORY_FAILURE_FIFO_SIZE);
1284         spinlock_t lock;
1285         struct work_struct work;
1286 };
1287 
1288 static DEFINE_PER_CPU(struct memory_failure_cpu, memory_failure_cpu);
1289 
1290 /**
1291  * memory_failure_queue - Schedule handling memory failure of a page.
1292  * @pfn: Page Number of the corrupted page
1293  * @trapno: Trap number reported in the signal to user space.
1294  * @flags: Flags for memory failure handling
1295  *
1296  * This function is called by the low level hardware error handler
1297  * when it detects hardware memory corruption of a page. It schedules
1298  * the recovering of error page, including dropping pages, killing
1299  * processes etc.
1300  *
1301  * The function is primarily of use for corruptions that
1302  * happen outside the current execution context (e.g. when
1303  * detected by a background scrubber)
1304  *
1305  * Can run in IRQ context.
1306  */
1307 void memory_failure_queue(unsigned long pfn, int trapno, int flags)
1308 {
1309         struct memory_failure_cpu *mf_cpu;
1310         unsigned long proc_flags;
1311         struct memory_failure_entry entry = {
1312                 .pfn =          pfn,
1313                 .trapno =       trapno,
1314                 .flags =        flags,
1315         };
1316 
1317         mf_cpu = &get_cpu_var(memory_failure_cpu);
1318         spin_lock_irqsave(&mf_cpu->lock, proc_flags);
1319         if (kfifo_put(&mf_cpu->fifo, entry))
1320                 schedule_work_on(smp_processor_id(), &mf_cpu->work);
1321         else
1322                 pr_err("Memory failure: buffer overflow when queuing memory failure at %#lx\n",
1323                        pfn);
1324         spin_unlock_irqrestore(&mf_cpu->lock, proc_flags);
1325         put_cpu_var(memory_failure_cpu);
1326 }
1327 EXPORT_SYMBOL_GPL(memory_failure_queue);
1328 
1329 static void memory_failure_work_func(struct work_struct *work)
1330 {
1331         struct memory_failure_cpu *mf_cpu;
1332         struct memory_failure_entry entry = { 0, };
1333         unsigned long proc_flags;
1334         int gotten;
1335 
1336         mf_cpu = this_cpu_ptr(&memory_failure_cpu);
1337         for (;;) {
1338                 spin_lock_irqsave(&mf_cpu->lock, proc_flags);
1339                 gotten = kfifo_get(&mf_cpu->fifo, &entry);
1340                 spin_unlock_irqrestore(&mf_cpu->lock, proc_flags);
1341                 if (!gotten)
1342                         break;
1343                 if (entry.flags & MF_SOFT_OFFLINE)
1344                         soft_offline_page(pfn_to_page(entry.pfn), entry.flags);
1345                 else
1346                         memory_failure(entry.pfn, entry.trapno, entry.flags);
1347         }
1348 }
1349 
1350 static int __init memory_failure_init(void)
1351 {
1352         struct memory_failure_cpu *mf_cpu;
1353         int cpu;
1354 
1355         for_each_possible_cpu(cpu) {
1356                 mf_cpu = &per_cpu(memory_failure_cpu, cpu);
1357                 spin_lock_init(&mf_cpu->lock);
1358                 INIT_KFIFO(mf_cpu->fifo);
1359                 INIT_WORK(&mf_cpu->work, memory_failure_work_func);
1360         }
1361 
1362         return 0;
1363 }
1364 core_initcall(memory_failure_init);
1365 
1366 #define unpoison_pr_info(fmt, pfn, rs)                  \
1367 ({                                                      \
1368         if (__ratelimit(rs))                            \
1369                 pr_info(fmt, pfn);                      \
1370 })
1371 
1372 /**
1373  * unpoison_memory - Unpoison a previously poisoned page
1374  * @pfn: Page number of the to be unpoisoned page
1375  *
1376  * Software-unpoison a page that has been poisoned by
1377  * memory_failure() earlier.
1378  *
1379  * This is only done on the software-level, so it only works
1380  * for linux injected failures, not real hardware failures
1381  *
1382  * Returns 0 for success, otherwise -errno.
1383  */
1384 int unpoison_memory(unsigned long pfn)
1385 {
1386         struct page *page;
1387         struct page *p;
1388         int freeit = 0;
1389         unsigned int nr_pages;
1390         static DEFINE_RATELIMIT_STATE(unpoison_rs, DEFAULT_RATELIMIT_INTERVAL,
1391                                         DEFAULT_RATELIMIT_BURST);
1392 
1393         if (!pfn_valid(pfn))
1394                 return -ENXIO;
1395 
1396         p = pfn_to_page(pfn);
1397         page = compound_head(p);
1398 
1399         if (!PageHWPoison(p)) {
1400                 unpoison_pr_info("Unpoison: Page was already unpoisoned %#lx\n",
1401                                  pfn, &unpoison_rs);
1402                 return 0;
1403         }
1404 
1405         if (page_count(page) > 1) {
1406                 unpoison_pr_info("Unpoison: Someone grabs the hwpoison page %#lx\n",
1407                                  pfn, &unpoison_rs);
1408                 return 0;
1409         }
1410 
1411         if (page_mapped(page)) {
1412                 unpoison_pr_info("Unpoison: Someone maps the hwpoison page %#lx\n",
1413                                  pfn, &unpoison_rs);
1414                 return 0;
1415         }
1416 
1417         if (page_mapping(page)) {
1418                 unpoison_pr_info("Unpoison: the hwpoison page has non-NULL mapping %#lx\n",
1419                                  pfn, &unpoison_rs);
1420                 return 0;
1421         }
1422 
1423         /*
1424          * unpoison_memory() can encounter thp only when the thp is being
1425          * worked by memory_failure() and the page lock is not held yet.
1426          * In such case, we yield to memory_failure() and make unpoison fail.
1427          */
1428         if (!PageHuge(page) && PageTransHuge(page)) {
1429                 unpoison_pr_info("Unpoison: Memory failure is now running on %#lx\n",
1430                                  pfn, &unpoison_rs);
1431                 return 0;
1432         }
1433 
1434         nr_pages = 1 << compound_order(page);
1435 
1436         if (!get_hwpoison_page(p)) {
1437                 /*
1438                  * Since HWPoisoned hugepage should have non-zero refcount,
1439                  * race between memory failure and unpoison seems to happen.
1440                  * In such case unpoison fails and memory failure runs
1441                  * to the end.
1442                  */
1443                 if (PageHuge(page)) {
1444                         unpoison_pr_info("Unpoison: Memory failure is now running on free hugepage %#lx\n",
1445                                          pfn, &unpoison_rs);
1446                         return 0;
1447                 }
1448                 if (TestClearPageHWPoison(p))
1449                         num_poisoned_pages_dec();
1450                 unpoison_pr_info("Unpoison: Software-unpoisoned free page %#lx\n",
1451                                  pfn, &unpoison_rs);
1452                 return 0;
1453         }
1454 
1455         lock_page(page);
1456         /*
1457          * This test is racy because PG_hwpoison is set outside of page lock.
1458          * That's acceptable because that won't trigger kernel panic. Instead,
1459          * the PG_hwpoison page will be caught and isolated on the entrance to
1460          * the free buddy page pool.
1461          */
1462         if (TestClearPageHWPoison(page)) {
1463                 unpoison_pr_info("Unpoison: Software-unpoisoned page %#lx\n",
1464                                  pfn, &unpoison_rs);
1465                 num_poisoned_pages_sub(nr_pages);
1466                 freeit = 1;
1467                 if (PageHuge(page))
1468                         clear_page_hwpoison_huge_page(page);
1469         }
1470         unlock_page(page);
1471 
1472         put_hwpoison_page(page);
1473         if (freeit && !(pfn == my_zero_pfn(0) && page_count(p) == 1))
1474                 put_hwpoison_page(page);
1475 
1476         return 0;
1477 }
1478 EXPORT_SYMBOL(unpoison_memory);
1479 
1480 static struct page *new_page(struct page *p, unsigned long private, int **x)
1481 {
1482         int nid = page_to_nid(p);
1483         if (PageHuge(p))
1484                 return alloc_huge_page_node(page_hstate(compound_head(p)),
1485                                                    nid);
1486         else
1487                 return __alloc_pages_node(nid, GFP_HIGHUSER_MOVABLE, 0);
1488 }
1489 
1490 /*
1491  * Safely get reference count of an arbitrary page.
1492  * Returns 0 for a free page, -EIO for a zero refcount page
1493  * that is not free, and 1 for any other page type.
1494  * For 1 the page is returned with increased page count, otherwise not.
1495  */
1496 static int __get_any_page(struct page *p, unsigned long pfn, int flags)
1497 {
1498         int ret;
1499 
1500         if (flags & MF_COUNT_INCREASED)
1501                 return 1;
1502 
1503         /*
1504          * When the target page is a free hugepage, just remove it
1505          * from free hugepage list.
1506          */
1507         if (!get_hwpoison_page(p)) {
1508                 if (PageHuge(p)) {
1509                         pr_info("%s: %#lx free huge page\n", __func__, pfn);
1510                         ret = 0;
1511                 } else if (is_free_buddy_page(p)) {
1512                         pr_info("%s: %#lx free buddy page\n", __func__, pfn);
1513                         ret = 0;
1514                 } else {
1515                         pr_info("%s: %#lx: unknown zero refcount page type %lx\n",
1516                                 __func__, pfn, p->flags);
1517                         ret = -EIO;
1518                 }
1519         } else {
1520                 /* Not a free page */
1521                 ret = 1;
1522         }
1523         return ret;
1524 }
1525 
1526 static int get_any_page(struct page *page, unsigned long pfn, int flags)
1527 {
1528         int ret = __get_any_page(page, pfn, flags);
1529 
1530         if (ret == 1 && !PageHuge(page) && !PageLRU(page)) {
1531                 /*
1532                  * Try to free it.
1533                  */
1534                 put_hwpoison_page(page);
1535                 shake_page(page, 1);
1536 
1537                 /*
1538                  * Did it turn free?
1539                  */
1540                 ret = __get_any_page(page, pfn, 0);
1541                 if (ret == 1 && !PageLRU(page)) {
1542                         /* Drop page reference which is from __get_any_page() */
1543                         put_hwpoison_page(page);
1544                         pr_info("soft_offline: %#lx: unknown non LRU page type %lx\n",
1545                                 pfn, page->flags);
1546                         return -EIO;
1547                 }
1548         }
1549         return ret;
1550 }
1551 
1552 static int soft_offline_huge_page(struct page *page, int flags)
1553 {
1554         int ret;
1555         unsigned long pfn = page_to_pfn(page);
1556         struct page *hpage = compound_head(page);
1557         LIST_HEAD(pagelist);
1558 
1559         /*
1560          * This double-check of PageHWPoison is to avoid the race with
1561          * memory_failure(). See also comment in __soft_offline_page().
1562          */
1563         lock_page(hpage);
1564         if (PageHWPoison(hpage)) {
1565                 unlock_page(hpage);
1566                 put_hwpoison_page(hpage);
1567                 pr_info("soft offline: %#lx hugepage already poisoned\n", pfn);
1568                 return -EBUSY;
1569         }
1570         unlock_page(hpage);
1571 
1572         ret = isolate_huge_page(hpage, &pagelist);
1573         /*
1574          * get_any_page() and isolate_huge_page() takes a refcount each,
1575          * so need to drop one here.
1576          */
1577         put_hwpoison_page(hpage);
1578         if (!ret) {
1579                 pr_info("soft offline: %#lx hugepage failed to isolate\n", pfn);
1580                 return -EBUSY;
1581         }
1582 
1583         ret = migrate_pages(&pagelist, new_page, NULL, MPOL_MF_MOVE_ALL,
1584                                 MIGRATE_SYNC, MR_MEMORY_FAILURE);
1585         if (ret) {
1586                 pr_info("soft offline: %#lx: migration failed %d, type %lx\n",
1587                         pfn, ret, page->flags);
1588                 /*
1589                  * We know that soft_offline_huge_page() tries to migrate
1590                  * only one hugepage pointed to by hpage, so we need not
1591                  * run through the pagelist here.
1592                  */
1593                 putback_active_hugepage(hpage);
1594                 if (ret > 0)
1595                         ret = -EIO;
1596         } else {
1597                 /* overcommit hugetlb page will be freed to buddy */
1598                 if (PageHuge(page)) {
1599                         set_page_hwpoison_huge_page(hpage);
1600                         dequeue_hwpoisoned_huge_page(hpage);
1601                         num_poisoned_pages_add(1 << compound_order(hpage));
1602                 } else {
1603                         SetPageHWPoison(page);
1604                         num_poisoned_pages_inc();
1605                 }
1606         }
1607         return ret;
1608 }
1609 
1610 static int __soft_offline_page(struct page *page, int flags)
1611 {
1612         int ret;
1613         unsigned long pfn = page_to_pfn(page);
1614 
1615         /*
1616          * Check PageHWPoison again inside page lock because PageHWPoison
1617          * is set by memory_failure() outside page lock. Note that
1618          * memory_failure() also double-checks PageHWPoison inside page lock,
1619          * so there's no race between soft_offline_page() and memory_failure().
1620          */
1621         lock_page(page);
1622         wait_on_page_writeback(page);
1623         if (PageHWPoison(page)) {
1624                 unlock_page(page);
1625                 put_hwpoison_page(page);
1626                 pr_info("soft offline: %#lx page already poisoned\n", pfn);
1627                 return -EBUSY;
1628         }
1629         /*
1630          * Try to invalidate first. This should work for
1631          * non dirty unmapped page cache pages.
1632          */
1633         ret = invalidate_inode_page(page);
1634         unlock_page(page);
1635         /*
1636          * RED-PEN would be better to keep it isolated here, but we
1637          * would need to fix isolation locking first.
1638          */
1639         if (ret == 1) {
1640                 put_hwpoison_page(page);
1641                 pr_info("soft_offline: %#lx: invalidated\n", pfn);
1642                 SetPageHWPoison(page);
1643                 num_poisoned_pages_inc();
1644                 return 0;
1645         }
1646 
1647         /*
1648          * Simple invalidation didn't work.
1649          * Try to migrate to a new page instead. migrate.c
1650          * handles a large number of cases for us.
1651          */
1652         ret = isolate_lru_page(page);
1653         /*
1654          * Drop page reference which is came from get_any_page()
1655          * successful isolate_lru_page() already took another one.
1656          */
1657         put_hwpoison_page(page);
1658         if (!ret) {
1659                 LIST_HEAD(pagelist);
1660                 inc_node_page_state(page, NR_ISOLATED_ANON +
1661                                         page_is_file_cache(page));
1662                 list_add(&page->lru, &pagelist);
1663                 ret = migrate_pages(&pagelist, new_page, NULL, MPOL_MF_MOVE_ALL,
1664                                         MIGRATE_SYNC, MR_MEMORY_FAILURE);
1665                 if (ret) {
1666                         if (!list_empty(&pagelist)) {
1667                                 list_del(&page->lru);
1668                                 dec_node_page_state(page, NR_ISOLATED_ANON +
1669                                                 page_is_file_cache(page));
1670                                 putback_lru_page(page);
1671                         }
1672 
1673                         pr_info("soft offline: %#lx: migration failed %d, type %lx\n",
1674                                 pfn, ret, page->flags);
1675                         if (ret > 0)
1676                                 ret = -EIO;
1677                 }
1678         } else {
1679                 pr_info("soft offline: %#lx: isolation failed: %d, page count %d, type %lx\n",
1680                         pfn, ret, page_count(page), page->flags);
1681         }
1682         return ret;
1683 }
1684 
1685 static int soft_offline_in_use_page(struct page *page, int flags)
1686 {
1687         int ret;
1688         struct page *hpage = compound_head(page);
1689 
1690         if (!PageHuge(page) && PageTransHuge(hpage)) {
1691                 lock_page(hpage);
1692                 if (!PageAnon(hpage) || unlikely(split_huge_page(hpage))) {
1693                         unlock_page(hpage);
1694                         if (!PageAnon(hpage))
1695                                 pr_info("soft offline: %#lx: non anonymous thp\n", page_to_pfn(page));
1696                         else
1697                                 pr_info("soft offline: %#lx: thp split failed\n", page_to_pfn(page));
1698                         put_hwpoison_page(hpage);
1699                         return -EBUSY;
1700                 }
1701                 unlock_page(hpage);
1702                 get_hwpoison_page(page);
1703                 put_hwpoison_page(hpage);
1704         }
1705 
1706         if (PageHuge(page))
1707                 ret = soft_offline_huge_page(page, flags);
1708         else
1709                 ret = __soft_offline_page(page, flags);
1710 
1711         return ret;
1712 }
1713 
1714 static void soft_offline_free_page(struct page *page)
1715 {
1716         if (PageHuge(page)) {
1717                 struct page *hpage = compound_head(page);
1718 
1719                 set_page_hwpoison_huge_page(hpage);
1720                 if (!dequeue_hwpoisoned_huge_page(hpage))
1721                         num_poisoned_pages_add(1 << compound_order(hpage));
1722         } else {
1723                 if (!TestSetPageHWPoison(page))
1724                         num_poisoned_pages_inc();
1725         }
1726 }
1727 
1728 /**
1729  * soft_offline_page - Soft offline a page.
1730  * @page: page to offline
1731  * @flags: flags. Same as memory_failure().
1732  *
1733  * Returns 0 on success, otherwise negated errno.
1734  *
1735  * Soft offline a page, by migration or invalidation,
1736  * without killing anything. This is for the case when
1737  * a page is not corrupted yet (so it's still valid to access),
1738  * but has had a number of corrected errors and is better taken
1739  * out.
1740  *
1741  * The actual policy on when to do that is maintained by
1742  * user space.
1743  *
1744  * This should never impact any application or cause data loss,
1745  * however it might take some time.
1746  *
1747  * This is not a 100% solution for all memory, but tries to be
1748  * ``good enough'' for the majority of memory.
1749  */
1750 int soft_offline_page(struct page *page, int flags)
1751 {
1752         int ret;
1753         unsigned long pfn = page_to_pfn(page);
1754 
1755         if (PageHWPoison(page)) {
1756                 pr_info("soft offline: %#lx page already poisoned\n", pfn);
1757                 if (flags & MF_COUNT_INCREASED)
1758                         put_hwpoison_page(page);
1759                 return -EBUSY;
1760         }
1761 
1762         get_online_mems();
1763         ret = get_any_page(page, pfn, flags);
1764         put_online_mems();
1765 
1766         if (ret > 0)
1767                 ret = soft_offline_in_use_page(page, flags);
1768         else if (ret == 0)
1769                 soft_offline_free_page(page);
1770 
1771         return ret;
1772 }
1773 

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