memory-failure.c revision af901ca181d92aac3a7dc265144a9081a86d8f39
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 2bit ECC memory or cache 11 * failure. 12 * 13 * Handles page cache pages in various states. The tricky part 14 * here is that we can access any page asynchronous to other VM 15 * users, because memory failures could happen anytime and anywhere, 16 * possibly violating some of their assumptions. This is why this code 17 * has to be extremely careful. Generally it tries to use normal locking 18 * rules, as in get the standard locks, even if that means the 19 * error handling takes potentially a long time. 20 * 21 * The operation to map back from RMAP chains to processes has to walk 22 * the complete process list and has non linear complexity with the number 23 * mappings. In short it can be quite slow. But since memory corruptions 24 * are rare we hope to get away with this. 25 */ 26 27/* 28 * Notebook: 29 * - hugetlb needs more code 30 * - kcore/oldmem/vmcore/mem/kmem check for hwpoison pages 31 * - pass bad pages to kdump next kernel 32 */ 33#define DEBUG 1 /* remove me in 2.6.34 */ 34#include <linux/kernel.h> 35#include <linux/mm.h> 36#include <linux/page-flags.h> 37#include <linux/sched.h> 38#include <linux/ksm.h> 39#include <linux/rmap.h> 40#include <linux/pagemap.h> 41#include <linux/swap.h> 42#include <linux/backing-dev.h> 43#include "internal.h" 44 45int sysctl_memory_failure_early_kill __read_mostly = 0; 46 47int sysctl_memory_failure_recovery __read_mostly = 1; 48 49atomic_long_t mce_bad_pages __read_mostly = ATOMIC_LONG_INIT(0); 50 51/* 52 * Send all the processes who have the page mapped an ``action optional'' 53 * signal. 54 */ 55static int kill_proc_ao(struct task_struct *t, unsigned long addr, int trapno, 56 unsigned long pfn) 57{ 58 struct siginfo si; 59 int ret; 60 61 printk(KERN_ERR 62 "MCE %#lx: Killing %s:%d early due to hardware memory corruption\n", 63 pfn, t->comm, t->pid); 64 si.si_signo = SIGBUS; 65 si.si_errno = 0; 66 si.si_code = BUS_MCEERR_AO; 67 si.si_addr = (void *)addr; 68#ifdef __ARCH_SI_TRAPNO 69 si.si_trapno = trapno; 70#endif 71 si.si_addr_lsb = PAGE_SHIFT; 72 /* 73 * Don't use force here, it's convenient if the signal 74 * can be temporarily blocked. 75 * This could cause a loop when the user sets SIGBUS 76 * to SIG_IGN, but hopefully noone will do that? 77 */ 78 ret = send_sig_info(SIGBUS, &si, t); /* synchronous? */ 79 if (ret < 0) 80 printk(KERN_INFO "MCE: Error sending signal to %s:%d: %d\n", 81 t->comm, t->pid, ret); 82 return ret; 83} 84 85/* 86 * Kill all processes that have a poisoned page mapped and then isolate 87 * the page. 88 * 89 * General strategy: 90 * Find all processes having the page mapped and kill them. 91 * But we keep a page reference around so that the page is not 92 * actually freed yet. 93 * Then stash the page away 94 * 95 * There's no convenient way to get back to mapped processes 96 * from the VMAs. So do a brute-force search over all 97 * running processes. 98 * 99 * Remember that machine checks are not common (or rather 100 * if they are common you have other problems), so this shouldn't 101 * be a performance issue. 102 * 103 * Also there are some races possible while we get from the 104 * error detection to actually handle it. 105 */ 106 107struct to_kill { 108 struct list_head nd; 109 struct task_struct *tsk; 110 unsigned long addr; 111 unsigned addr_valid:1; 112}; 113 114/* 115 * Failure handling: if we can't find or can't kill a process there's 116 * not much we can do. We just print a message and ignore otherwise. 117 */ 118 119/* 120 * Schedule a process for later kill. 121 * Uses GFP_ATOMIC allocations to avoid potential recursions in the VM. 122 * TBD would GFP_NOIO be enough? 123 */ 124static void add_to_kill(struct task_struct *tsk, struct page *p, 125 struct vm_area_struct *vma, 126 struct list_head *to_kill, 127 struct to_kill **tkc) 128{ 129 struct to_kill *tk; 130 131 if (*tkc) { 132 tk = *tkc; 133 *tkc = NULL; 134 } else { 135 tk = kmalloc(sizeof(struct to_kill), GFP_ATOMIC); 136 if (!tk) { 137 printk(KERN_ERR 138 "MCE: Out of memory while machine check handling\n"); 139 return; 140 } 141 } 142 tk->addr = page_address_in_vma(p, vma); 143 tk->addr_valid = 1; 144 145 /* 146 * In theory we don't have to kill when the page was 147 * munmaped. But it could be also a mremap. Since that's 148 * likely very rare kill anyways just out of paranoia, but use 149 * a SIGKILL because the error is not contained anymore. 150 */ 151 if (tk->addr == -EFAULT) { 152 pr_debug("MCE: Unable to find user space address %lx in %s\n", 153 page_to_pfn(p), tsk->comm); 154 tk->addr_valid = 0; 155 } 156 get_task_struct(tsk); 157 tk->tsk = tsk; 158 list_add_tail(&tk->nd, to_kill); 159} 160 161/* 162 * Kill the processes that have been collected earlier. 163 * 164 * Only do anything when DOIT is set, otherwise just free the list 165 * (this is used for clean pages which do not need killing) 166 * Also when FAIL is set do a force kill because something went 167 * wrong earlier. 168 */ 169static void kill_procs_ao(struct list_head *to_kill, int doit, int trapno, 170 int fail, unsigned long pfn) 171{ 172 struct to_kill *tk, *next; 173 174 list_for_each_entry_safe (tk, next, to_kill, nd) { 175 if (doit) { 176 /* 177 * In case something went wrong with munmapping 178 * make sure the process doesn't catch the 179 * signal and then access the memory. Just kill it. 180 * the signal handlers 181 */ 182 if (fail || tk->addr_valid == 0) { 183 printk(KERN_ERR 184 "MCE %#lx: forcibly killing %s:%d because of failure to unmap corrupted page\n", 185 pfn, tk->tsk->comm, tk->tsk->pid); 186 force_sig(SIGKILL, tk->tsk); 187 } 188 189 /* 190 * In theory the process could have mapped 191 * something else on the address in-between. We could 192 * check for that, but we need to tell the 193 * process anyways. 194 */ 195 else if (kill_proc_ao(tk->tsk, tk->addr, trapno, 196 pfn) < 0) 197 printk(KERN_ERR 198 "MCE %#lx: Cannot send advisory machine check signal to %s:%d\n", 199 pfn, tk->tsk->comm, tk->tsk->pid); 200 } 201 put_task_struct(tk->tsk); 202 kfree(tk); 203 } 204} 205 206static int task_early_kill(struct task_struct *tsk) 207{ 208 if (!tsk->mm) 209 return 0; 210 if (tsk->flags & PF_MCE_PROCESS) 211 return !!(tsk->flags & PF_MCE_EARLY); 212 return sysctl_memory_failure_early_kill; 213} 214 215/* 216 * Collect processes when the error hit an anonymous page. 217 */ 218static void collect_procs_anon(struct page *page, struct list_head *to_kill, 219 struct to_kill **tkc) 220{ 221 struct vm_area_struct *vma; 222 struct task_struct *tsk; 223 struct anon_vma *av; 224 225 read_lock(&tasklist_lock); 226 av = page_lock_anon_vma(page); 227 if (av == NULL) /* Not actually mapped anymore */ 228 goto out; 229 for_each_process (tsk) { 230 if (!task_early_kill(tsk)) 231 continue; 232 list_for_each_entry (vma, &av->head, anon_vma_node) { 233 if (!page_mapped_in_vma(page, vma)) 234 continue; 235 if (vma->vm_mm == tsk->mm) 236 add_to_kill(tsk, page, vma, to_kill, tkc); 237 } 238 } 239 page_unlock_anon_vma(av); 240out: 241 read_unlock(&tasklist_lock); 242} 243 244/* 245 * Collect processes when the error hit a file mapped page. 246 */ 247static void collect_procs_file(struct page *page, struct list_head *to_kill, 248 struct to_kill **tkc) 249{ 250 struct vm_area_struct *vma; 251 struct task_struct *tsk; 252 struct prio_tree_iter iter; 253 struct address_space *mapping = page->mapping; 254 255 /* 256 * A note on the locking order between the two locks. 257 * We don't rely on this particular order. 258 * If you have some other code that needs a different order 259 * feel free to switch them around. Or add a reverse link 260 * from mm_struct to task_struct, then this could be all 261 * done without taking tasklist_lock and looping over all tasks. 262 */ 263 264 read_lock(&tasklist_lock); 265 spin_lock(&mapping->i_mmap_lock); 266 for_each_process(tsk) { 267 pgoff_t pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT); 268 269 if (!task_early_kill(tsk)) 270 continue; 271 272 vma_prio_tree_foreach(vma, &iter, &mapping->i_mmap, pgoff, 273 pgoff) { 274 /* 275 * Send early kill signal to tasks where a vma covers 276 * the page but the corrupted page is not necessarily 277 * mapped it in its pte. 278 * Assume applications who requested early kill want 279 * to be informed of all such data corruptions. 280 */ 281 if (vma->vm_mm == tsk->mm) 282 add_to_kill(tsk, page, vma, to_kill, tkc); 283 } 284 } 285 spin_unlock(&mapping->i_mmap_lock); 286 read_unlock(&tasklist_lock); 287} 288 289/* 290 * Collect the processes who have the corrupted page mapped to kill. 291 * This is done in two steps for locking reasons. 292 * First preallocate one tokill structure outside the spin locks, 293 * so that we can kill at least one process reasonably reliable. 294 */ 295static void collect_procs(struct page *page, struct list_head *tokill) 296{ 297 struct to_kill *tk; 298 299 if (!page->mapping) 300 return; 301 302 tk = kmalloc(sizeof(struct to_kill), GFP_NOIO); 303 if (!tk) 304 return; 305 if (PageAnon(page)) 306 collect_procs_anon(page, tokill, &tk); 307 else 308 collect_procs_file(page, tokill, &tk); 309 kfree(tk); 310} 311 312/* 313 * Error handlers for various types of pages. 314 */ 315 316enum outcome { 317 FAILED, /* Error handling failed */ 318 DELAYED, /* Will be handled later */ 319 IGNORED, /* Error safely ignored */ 320 RECOVERED, /* Successfully recovered */ 321}; 322 323static const char *action_name[] = { 324 [FAILED] = "Failed", 325 [DELAYED] = "Delayed", 326 [IGNORED] = "Ignored", 327 [RECOVERED] = "Recovered", 328}; 329 330/* 331 * Error hit kernel page. 332 * Do nothing, try to be lucky and not touch this instead. For a few cases we 333 * could be more sophisticated. 334 */ 335static int me_kernel(struct page *p, unsigned long pfn) 336{ 337 return DELAYED; 338} 339 340/* 341 * Already poisoned page. 342 */ 343static int me_ignore(struct page *p, unsigned long pfn) 344{ 345 return IGNORED; 346} 347 348/* 349 * Page in unknown state. Do nothing. 350 */ 351static int me_unknown(struct page *p, unsigned long pfn) 352{ 353 printk(KERN_ERR "MCE %#lx: Unknown page state\n", pfn); 354 return FAILED; 355} 356 357/* 358 * Free memory 359 */ 360static int me_free(struct page *p, unsigned long pfn) 361{ 362 return DELAYED; 363} 364 365/* 366 * Clean (or cleaned) page cache page. 367 */ 368static int me_pagecache_clean(struct page *p, unsigned long pfn) 369{ 370 int err; 371 int ret = FAILED; 372 struct address_space *mapping; 373 374 /* 375 * For anonymous pages we're done the only reference left 376 * should be the one m_f() holds. 377 */ 378 if (PageAnon(p)) 379 return RECOVERED; 380 381 /* 382 * Now truncate the page in the page cache. This is really 383 * more like a "temporary hole punch" 384 * Don't do this for block devices when someone else 385 * has a reference, because it could be file system metadata 386 * and that's not safe to truncate. 387 */ 388 mapping = page_mapping(p); 389 if (!mapping) { 390 /* 391 * Page has been teared down in the meanwhile 392 */ 393 return FAILED; 394 } 395 396 /* 397 * Truncation is a bit tricky. Enable it per file system for now. 398 * 399 * Open: to take i_mutex or not for this? Right now we don't. 400 */ 401 if (mapping->a_ops->error_remove_page) { 402 err = mapping->a_ops->error_remove_page(mapping, p); 403 if (err != 0) { 404 printk(KERN_INFO "MCE %#lx: Failed to punch page: %d\n", 405 pfn, err); 406 } else if (page_has_private(p) && 407 !try_to_release_page(p, GFP_NOIO)) { 408 pr_debug("MCE %#lx: failed to release buffers\n", pfn); 409 } else { 410 ret = RECOVERED; 411 } 412 } else { 413 /* 414 * If the file system doesn't support it just invalidate 415 * This fails on dirty or anything with private pages 416 */ 417 if (invalidate_inode_page(p)) 418 ret = RECOVERED; 419 else 420 printk(KERN_INFO "MCE %#lx: Failed to invalidate\n", 421 pfn); 422 } 423 return ret; 424} 425 426/* 427 * Dirty cache page page 428 * Issues: when the error hit a hole page the error is not properly 429 * propagated. 430 */ 431static int me_pagecache_dirty(struct page *p, unsigned long pfn) 432{ 433 struct address_space *mapping = page_mapping(p); 434 435 SetPageError(p); 436 /* TBD: print more information about the file. */ 437 if (mapping) { 438 /* 439 * IO error will be reported by write(), fsync(), etc. 440 * who check the mapping. 441 * This way the application knows that something went 442 * wrong with its dirty file data. 443 * 444 * There's one open issue: 445 * 446 * The EIO will be only reported on the next IO 447 * operation and then cleared through the IO map. 448 * Normally Linux has two mechanisms to pass IO error 449 * first through the AS_EIO flag in the address space 450 * and then through the PageError flag in the page. 451 * Since we drop pages on memory failure handling the 452 * only mechanism open to use is through AS_AIO. 453 * 454 * This has the disadvantage that it gets cleared on 455 * the first operation that returns an error, while 456 * the PageError bit is more sticky and only cleared 457 * when the page is reread or dropped. If an 458 * application assumes it will always get error on 459 * fsync, but does other operations on the fd before 460 * and the page is dropped inbetween then the error 461 * will not be properly reported. 462 * 463 * This can already happen even without hwpoisoned 464 * pages: first on metadata IO errors (which only 465 * report through AS_EIO) or when the page is dropped 466 * at the wrong time. 467 * 468 * So right now we assume that the application DTRT on 469 * the first EIO, but we're not worse than other parts 470 * of the kernel. 471 */ 472 mapping_set_error(mapping, EIO); 473 } 474 475 return me_pagecache_clean(p, pfn); 476} 477 478/* 479 * Clean and dirty swap cache. 480 * 481 * Dirty swap cache page is tricky to handle. The page could live both in page 482 * cache and swap cache(ie. page is freshly swapped in). So it could be 483 * referenced concurrently by 2 types of PTEs: 484 * normal PTEs and swap PTEs. We try to handle them consistently by calling 485 * try_to_unmap(TTU_IGNORE_HWPOISON) to convert the normal PTEs to swap PTEs, 486 * and then 487 * - clear dirty bit to prevent IO 488 * - remove from LRU 489 * - but keep in the swap cache, so that when we return to it on 490 * a later page fault, we know the application is accessing 491 * corrupted data and shall be killed (we installed simple 492 * interception code in do_swap_page to catch it). 493 * 494 * Clean swap cache pages can be directly isolated. A later page fault will 495 * bring in the known good data from disk. 496 */ 497static int me_swapcache_dirty(struct page *p, unsigned long pfn) 498{ 499 ClearPageDirty(p); 500 /* Trigger EIO in shmem: */ 501 ClearPageUptodate(p); 502 503 return DELAYED; 504} 505 506static int me_swapcache_clean(struct page *p, unsigned long pfn) 507{ 508 delete_from_swap_cache(p); 509 510 return RECOVERED; 511} 512 513/* 514 * Huge pages. Needs work. 515 * Issues: 516 * No rmap support so we cannot find the original mapper. In theory could walk 517 * all MMs and look for the mappings, but that would be non atomic and racy. 518 * Need rmap for hugepages for this. Alternatively we could employ a heuristic, 519 * like just walking the current process and hoping it has it mapped (that 520 * should be usually true for the common "shared database cache" case) 521 * Should handle free huge pages and dequeue them too, but this needs to 522 * handle huge page accounting correctly. 523 */ 524static int me_huge_page(struct page *p, unsigned long pfn) 525{ 526 return FAILED; 527} 528 529/* 530 * Various page states we can handle. 531 * 532 * A page state is defined by its current page->flags bits. 533 * The table matches them in order and calls the right handler. 534 * 535 * This is quite tricky because we can access page at any time 536 * in its live cycle, so all accesses have to be extremly careful. 537 * 538 * This is not complete. More states could be added. 539 * For any missing state don't attempt recovery. 540 */ 541 542#define dirty (1UL << PG_dirty) 543#define sc (1UL << PG_swapcache) 544#define unevict (1UL << PG_unevictable) 545#define mlock (1UL << PG_mlocked) 546#define writeback (1UL << PG_writeback) 547#define lru (1UL << PG_lru) 548#define swapbacked (1UL << PG_swapbacked) 549#define head (1UL << PG_head) 550#define tail (1UL << PG_tail) 551#define compound (1UL << PG_compound) 552#define slab (1UL << PG_slab) 553#define buddy (1UL << PG_buddy) 554#define reserved (1UL << PG_reserved) 555 556static struct page_state { 557 unsigned long mask; 558 unsigned long res; 559 char *msg; 560 int (*action)(struct page *p, unsigned long pfn); 561} error_states[] = { 562 { reserved, reserved, "reserved kernel", me_ignore }, 563 { buddy, buddy, "free kernel", me_free }, 564 565 /* 566 * Could in theory check if slab page is free or if we can drop 567 * currently unused objects without touching them. But just 568 * treat it as standard kernel for now. 569 */ 570 { slab, slab, "kernel slab", me_kernel }, 571 572#ifdef CONFIG_PAGEFLAGS_EXTENDED 573 { head, head, "huge", me_huge_page }, 574 { tail, tail, "huge", me_huge_page }, 575#else 576 { compound, compound, "huge", me_huge_page }, 577#endif 578 579 { sc|dirty, sc|dirty, "swapcache", me_swapcache_dirty }, 580 { sc|dirty, sc, "swapcache", me_swapcache_clean }, 581 582 { unevict|dirty, unevict|dirty, "unevictable LRU", me_pagecache_dirty}, 583 { unevict, unevict, "unevictable LRU", me_pagecache_clean}, 584 585#ifdef CONFIG_HAVE_MLOCKED_PAGE_BIT 586 { mlock|dirty, mlock|dirty, "mlocked LRU", me_pagecache_dirty }, 587 { mlock, mlock, "mlocked LRU", me_pagecache_clean }, 588#endif 589 590 { lru|dirty, lru|dirty, "LRU", me_pagecache_dirty }, 591 { lru|dirty, lru, "clean LRU", me_pagecache_clean }, 592 { swapbacked, swapbacked, "anonymous", me_pagecache_clean }, 593 594 /* 595 * Catchall entry: must be at end. 596 */ 597 { 0, 0, "unknown page state", me_unknown }, 598}; 599 600static void action_result(unsigned long pfn, char *msg, int result) 601{ 602 struct page *page = NULL; 603 if (pfn_valid(pfn)) 604 page = pfn_to_page(pfn); 605 606 printk(KERN_ERR "MCE %#lx: %s%s page recovery: %s\n", 607 pfn, 608 page && PageDirty(page) ? "dirty " : "", 609 msg, action_name[result]); 610} 611 612static int page_action(struct page_state *ps, struct page *p, 613 unsigned long pfn, int ref) 614{ 615 int result; 616 int count; 617 618 result = ps->action(p, pfn); 619 action_result(pfn, ps->msg, result); 620 621 count = page_count(p) - 1 - ref; 622 if (count != 0) 623 printk(KERN_ERR 624 "MCE %#lx: %s page still referenced by %d users\n", 625 pfn, ps->msg, count); 626 627 /* Could do more checks here if page looks ok */ 628 /* 629 * Could adjust zone counters here to correct for the missing page. 630 */ 631 632 return result == RECOVERED ? 0 : -EBUSY; 633} 634 635#define N_UNMAP_TRIES 5 636 637/* 638 * Do all that is necessary to remove user space mappings. Unmap 639 * the pages and send SIGBUS to the processes if the data was dirty. 640 */ 641static void hwpoison_user_mappings(struct page *p, unsigned long pfn, 642 int trapno) 643{ 644 enum ttu_flags ttu = TTU_UNMAP | TTU_IGNORE_MLOCK | TTU_IGNORE_ACCESS; 645 struct address_space *mapping; 646 LIST_HEAD(tokill); 647 int ret; 648 int i; 649 int kill = 1; 650 651 if (PageReserved(p) || PageCompound(p) || PageSlab(p) || PageKsm(p)) 652 return; 653 654 /* 655 * This check implies we don't kill processes if their pages 656 * are in the swap cache early. Those are always late kills. 657 */ 658 if (!page_mapped(p)) 659 return; 660 661 if (PageSwapCache(p)) { 662 printk(KERN_ERR 663 "MCE %#lx: keeping poisoned page in swap cache\n", pfn); 664 ttu |= TTU_IGNORE_HWPOISON; 665 } 666 667 /* 668 * Propagate the dirty bit from PTEs to struct page first, because we 669 * need this to decide if we should kill or just drop the page. 670 */ 671 mapping = page_mapping(p); 672 if (!PageDirty(p) && mapping && mapping_cap_writeback_dirty(mapping)) { 673 if (page_mkclean(p)) { 674 SetPageDirty(p); 675 } else { 676 kill = 0; 677 ttu |= TTU_IGNORE_HWPOISON; 678 printk(KERN_INFO 679 "MCE %#lx: corrupted page was clean: dropped without side effects\n", 680 pfn); 681 } 682 } 683 684 /* 685 * First collect all the processes that have the page 686 * mapped in dirty form. This has to be done before try_to_unmap, 687 * because ttu takes the rmap data structures down. 688 * 689 * Error handling: We ignore errors here because 690 * there's nothing that can be done. 691 */ 692 if (kill) 693 collect_procs(p, &tokill); 694 695 /* 696 * try_to_unmap can fail temporarily due to races. 697 * Try a few times (RED-PEN better strategy?) 698 */ 699 for (i = 0; i < N_UNMAP_TRIES; i++) { 700 ret = try_to_unmap(p, ttu); 701 if (ret == SWAP_SUCCESS) 702 break; 703 pr_debug("MCE %#lx: try_to_unmap retry needed %d\n", pfn, ret); 704 } 705 706 if (ret != SWAP_SUCCESS) 707 printk(KERN_ERR "MCE %#lx: failed to unmap page (mapcount=%d)\n", 708 pfn, page_mapcount(p)); 709 710 /* 711 * Now that the dirty bit has been propagated to the 712 * struct page and all unmaps done we can decide if 713 * killing is needed or not. Only kill when the page 714 * was dirty, otherwise the tokill list is merely 715 * freed. When there was a problem unmapping earlier 716 * use a more force-full uncatchable kill to prevent 717 * any accesses to the poisoned memory. 718 */ 719 kill_procs_ao(&tokill, !!PageDirty(p), trapno, 720 ret != SWAP_SUCCESS, pfn); 721} 722 723int __memory_failure(unsigned long pfn, int trapno, int ref) 724{ 725 unsigned long lru_flag; 726 struct page_state *ps; 727 struct page *p; 728 int res; 729 730 if (!sysctl_memory_failure_recovery) 731 panic("Memory failure from trap %d on page %lx", trapno, pfn); 732 733 if (!pfn_valid(pfn)) { 734 action_result(pfn, "memory outside kernel control", IGNORED); 735 return -EIO; 736 } 737 738 p = pfn_to_page(pfn); 739 if (TestSetPageHWPoison(p)) { 740 action_result(pfn, "already hardware poisoned", IGNORED); 741 return 0; 742 } 743 744 atomic_long_add(1, &mce_bad_pages); 745 746 /* 747 * We need/can do nothing about count=0 pages. 748 * 1) it's a free page, and therefore in safe hand: 749 * prep_new_page() will be the gate keeper. 750 * 2) it's part of a non-compound high order page. 751 * Implies some kernel user: cannot stop them from 752 * R/W the page; let's pray that the page has been 753 * used and will be freed some time later. 754 * In fact it's dangerous to directly bump up page count from 0, 755 * that may make page_freeze_refs()/page_unfreeze_refs() mismatch. 756 */ 757 if (!get_page_unless_zero(compound_head(p))) { 758 action_result(pfn, "free or high order kernel", IGNORED); 759 return PageBuddy(compound_head(p)) ? 0 : -EBUSY; 760 } 761 762 /* 763 * We ignore non-LRU pages for good reasons. 764 * - PG_locked is only well defined for LRU pages and a few others 765 * - to avoid races with __set_page_locked() 766 * - to avoid races with __SetPageSlab*() (and more non-atomic ops) 767 * The check (unnecessarily) ignores LRU pages being isolated and 768 * walked by the page reclaim code, however that's not a big loss. 769 */ 770 if (!PageLRU(p)) 771 lru_add_drain_all(); 772 lru_flag = p->flags & lru; 773 if (isolate_lru_page(p)) { 774 action_result(pfn, "non LRU", IGNORED); 775 put_page(p); 776 return -EBUSY; 777 } 778 page_cache_release(p); 779 780 /* 781 * Lock the page and wait for writeback to finish. 782 * It's very difficult to mess with pages currently under IO 783 * and in many cases impossible, so we just avoid it here. 784 */ 785 lock_page_nosync(p); 786 wait_on_page_writeback(p); 787 788 /* 789 * Now take care of user space mappings. 790 */ 791 hwpoison_user_mappings(p, pfn, trapno); 792 793 /* 794 * Torn down by someone else? 795 */ 796 if ((lru_flag & lru) && !PageSwapCache(p) && p->mapping == NULL) { 797 action_result(pfn, "already truncated LRU", IGNORED); 798 res = 0; 799 goto out; 800 } 801 802 res = -EBUSY; 803 for (ps = error_states;; ps++) { 804 if (((p->flags | lru_flag)& ps->mask) == ps->res) { 805 res = page_action(ps, p, pfn, ref); 806 break; 807 } 808 } 809out: 810 unlock_page(p); 811 return res; 812} 813EXPORT_SYMBOL_GPL(__memory_failure); 814 815/** 816 * memory_failure - Handle memory failure of a page. 817 * @pfn: Page Number of the corrupted page 818 * @trapno: Trap number reported in the signal to user space. 819 * 820 * This function is called by the low level machine check code 821 * of an architecture when it detects hardware memory corruption 822 * of a page. It tries its best to recover, which includes 823 * dropping pages, killing processes etc. 824 * 825 * The function is primarily of use for corruptions that 826 * happen outside the current execution context (e.g. when 827 * detected by a background scrubber) 828 * 829 * Must run in process context (e.g. a work queue) with interrupts 830 * enabled and no spinlocks hold. 831 */ 832void memory_failure(unsigned long pfn, int trapno) 833{ 834 __memory_failure(pfn, trapno, 0); 835} 836