/* * Copyright (C) 2008, 2009 Intel Corporation * Authors: Andi Kleen, Fengguang Wu * * This software may be redistributed and/or modified under the terms of * the GNU General Public License ("GPL") version 2 only as published by the * Free Software Foundation. * * High level machine check handler. Handles pages reported by the * hardware as being corrupted usually due to a 2bit ECC memory or cache * failure. * * Handles page cache pages in various states. The tricky part * here is that we can access any page asynchronous to other VM * users, because memory failures could happen anytime and anywhere, * possibly violating some of their assumptions. This is why this code * has to be extremely careful. Generally it tries to use normal locking * rules, as in get the standard locks, even if that means the * error handling takes potentially a long time. * * The operation to map back from RMAP chains to processes has to walk * the complete process list and has non linear complexity with the number * mappings. In short it can be quite slow. But since memory corruptions * are rare we hope to get away with this. */ /* * Notebook: * - hugetlb needs more code * - kcore/oldmem/vmcore/mem/kmem check for hwpoison pages * - pass bad pages to kdump next kernel */ #define DEBUG 1 /* remove me in 2.6.34 */ #include <linux/kernel.h> #include <linux/mm.h> #include <linux/page-flags.h> #include <linux/kernel-page-flags.h> #include <linux/sched.h> #include <linux/ksm.h> #include <linux/rmap.h> #include <linux/pagemap.h> #include <linux/swap.h> #include <linux/backing-dev.h> #include <linux/migrate.h> #include <linux/page-isolation.h> #include <linux/suspend.h> #include "internal.h" int sysctl_memory_failure_early_kill __read_mostly = 0; int sysctl_memory_failure_recovery __read_mostly = 1; atomic_long_t mce_bad_pages __read_mostly = ATOMIC_LONG_INIT(0); #if defined(CONFIG_HWPOISON_INJECT) || defined(CONFIG_HWPOISON_INJECT_MODULE) u32 hwpoison_filter_enable = 0; u32 hwpoison_filter_dev_major = ~0U; u32 hwpoison_filter_dev_minor = ~0U; u64 hwpoison_filter_flags_mask; u64 hwpoison_filter_flags_value; EXPORT_SYMBOL_GPL(hwpoison_filter_enable); EXPORT_SYMBOL_GPL(hwpoison_filter_dev_major); EXPORT_SYMBOL_GPL(hwpoison_filter_dev_minor); EXPORT_SYMBOL_GPL(hwpoison_filter_flags_mask); EXPORT_SYMBOL_GPL(hwpoison_filter_flags_value); static int hwpoison_filter_dev(struct page *p) { struct address_space *mapping; dev_t dev; if (hwpoison_filter_dev_major == ~0U && hwpoison_filter_dev_minor == ~0U) return 0; /* * page_mapping() does not accept slab page */ if (PageSlab(p)) return -EINVAL; mapping = page_mapping(p); if (mapping == NULL || mapping->host == NULL) return -EINVAL; dev = mapping->host->i_sb->s_dev; if (hwpoison_filter_dev_major != ~0U && hwpoison_filter_dev_major != MAJOR(dev)) return -EINVAL; if (hwpoison_filter_dev_minor != ~0U && hwpoison_filter_dev_minor != MINOR(dev)) return -EINVAL; return 0; } static int hwpoison_filter_flags(struct page *p) { if (!hwpoison_filter_flags_mask) return 0; if ((stable_page_flags(p) & hwpoison_filter_flags_mask) == hwpoison_filter_flags_value) return 0; else return -EINVAL; } /* * This allows stress tests to limit test scope to a collection of tasks * by putting them under some memcg. This prevents killing unrelated/important * processes such as /sbin/init. Note that the target task may share clean * pages with init (eg. libc text), which is harmless. If the target task * share _dirty_ pages with another task B, the test scheme must make sure B * is also included in the memcg. At last, due to race conditions this filter * can only guarantee that the page either belongs to the memcg tasks, or is * a freed page. */ #ifdef CONFIG_CGROUP_MEM_RES_CTLR_SWAP u64 hwpoison_filter_memcg; EXPORT_SYMBOL_GPL(hwpoison_filter_memcg); static int hwpoison_filter_task(struct page *p) { struct mem_cgroup *mem; struct cgroup_subsys_state *css; unsigned long ino; if (!hwpoison_filter_memcg) return 0; mem = try_get_mem_cgroup_from_page(p); if (!mem) return -EINVAL; css = mem_cgroup_css(mem); /* root_mem_cgroup has NULL dentries */ if (!css->cgroup->dentry) return -EINVAL; ino = css->cgroup->dentry->d_inode->i_ino; css_put(css); if (ino != hwpoison_filter_memcg) return -EINVAL; return 0; } #else static int hwpoison_filter_task(struct page *p) { return 0; } #endif int hwpoison_filter(struct page *p) { if (!hwpoison_filter_enable) return 0; if (hwpoison_filter_dev(p)) return -EINVAL; if (hwpoison_filter_flags(p)) return -EINVAL; if (hwpoison_filter_task(p)) return -EINVAL; return 0; } #else int hwpoison_filter(struct page *p) { return 0; } #endif EXPORT_SYMBOL_GPL(hwpoison_filter); /* * Send all the processes who have the page mapped an ``action optional'' * signal. */ static int kill_proc_ao(struct task_struct *t, unsigned long addr, int trapno, unsigned long pfn) { struct siginfo si; int ret; printk(KERN_ERR "MCE %#lx: Killing %s:%d early due to hardware memory corruption\n", pfn, t->comm, t->pid); si.si_signo = SIGBUS; si.si_errno = 0; si.si_code = BUS_MCEERR_AO; si.si_addr = (void *)addr; #ifdef __ARCH_SI_TRAPNO si.si_trapno = trapno; #endif si.si_addr_lsb = PAGE_SHIFT; /* * Don't use force here, it's convenient if the signal * can be temporarily blocked. * This could cause a loop when the user sets SIGBUS * to SIG_IGN, but hopefully noone will do that? */ ret = send_sig_info(SIGBUS, &si, t); /* synchronous? */ if (ret < 0) printk(KERN_INFO "MCE: Error sending signal to %s:%d: %d\n", t->comm, t->pid, ret); return ret; } /* * When a unknown page type is encountered drain as many buffers as possible * in the hope to turn the page into a LRU or free page, which we can handle. */ void shake_page(struct page *p, int access) { if (!PageSlab(p)) { lru_add_drain_all(); if (PageLRU(p)) return; drain_all_pages(); if (PageLRU(p) || is_free_buddy_page(p)) return; } /* * Only all shrink_slab here (which would also * shrink other caches) if access is not potentially fatal. */ if (access) { int nr; do { nr = shrink_slab(1000, GFP_KERNEL, 1000); if (page_count(p) == 0) break; } while (nr > 10); } } EXPORT_SYMBOL_GPL(shake_page); /* * Kill all processes that have a poisoned page mapped and then isolate * the page. * * General strategy: * Find all processes having the page mapped and kill them. * But we keep a page reference around so that the page is not * actually freed yet. * Then stash the page away * * There's no convenient way to get back to mapped processes * from the VMAs. So do a brute-force search over all * running processes. * * Remember that machine checks are not common (or rather * if they are common you have other problems), so this shouldn't * be a performance issue. * * Also there are some races possible while we get from the * error detection to actually handle it. */ struct to_kill { struct list_head nd; struct task_struct *tsk; unsigned long addr; unsigned addr_valid:1; }; /* * Failure handling: if we can't find or can't kill a process there's * not much we can do. We just print a message and ignore otherwise. */ /* * Schedule a process for later kill. * Uses GFP_ATOMIC allocations to avoid potential recursions in the VM. * TBD would GFP_NOIO be enough? */ static void add_to_kill(struct task_struct *tsk, struct page *p, struct vm_area_struct *vma, struct list_head *to_kill, struct to_kill **tkc) { struct to_kill *tk; if (*tkc) { tk = *tkc; *tkc = NULL; } else { tk = kmalloc(sizeof(struct to_kill), GFP_ATOMIC); if (!tk) { printk(KERN_ERR "MCE: Out of memory while machine check handling\n"); return; } } tk->addr = page_address_in_vma(p, vma); tk->addr_valid = 1; /* * In theory we don't have to kill when the page was * munmaped. But it could be also a mremap. Since that's * likely very rare kill anyways just out of paranoia, but use * a SIGKILL because the error is not contained anymore. */ if (tk->addr == -EFAULT) { pr_debug("MCE: Unable to find user space address %lx in %s\n", page_to_pfn(p), tsk->comm); tk->addr_valid = 0; } get_task_struct(tsk); tk->tsk = tsk; list_add_tail(&tk->nd, to_kill); } /* * Kill the processes that have been collected earlier. * * Only do anything when DOIT is set, otherwise just free the list * (this is used for clean pages which do not need killing) * Also when FAIL is set do a force kill because something went * wrong earlier. */ static void kill_procs_ao(struct list_head *to_kill, int doit, int trapno, int fail, unsigned long pfn) { struct to_kill *tk, *next; list_for_each_entry_safe (tk, next, to_kill, nd) { if (doit) { /* * In case something went wrong with munmapping * make sure the process doesn't catch the * signal and then access the memory. Just kill it. */ if (fail || tk->addr_valid == 0) { printk(KERN_ERR "MCE %#lx: forcibly killing %s:%d because of failure to unmap corrupted page\n", pfn, tk->tsk->comm, tk->tsk->pid); force_sig(SIGKILL, tk->tsk); } /* * In theory the process could have mapped * something else on the address in-between. We could * check for that, but we need to tell the * process anyways. */ else if (kill_proc_ao(tk->tsk, tk->addr, trapno, pfn) < 0) printk(KERN_ERR "MCE %#lx: Cannot send advisory machine check signal to %s:%d\n", pfn, tk->tsk->comm, tk->tsk->pid); } put_task_struct(tk->tsk); kfree(tk); } } static int task_early_kill(struct task_struct *tsk) { if (!tsk->mm) return 0; if (tsk->flags & PF_MCE_PROCESS) return !!(tsk->flags & PF_MCE_EARLY); return sysctl_memory_failure_early_kill; } /* * Collect processes when the error hit an anonymous page. */ static void collect_procs_anon(struct page *page, struct list_head *to_kill, struct to_kill **tkc) { struct vm_area_struct *vma; struct task_struct *tsk; struct anon_vma *av; read_lock(&tasklist_lock); av = page_lock_anon_vma(page); if (av == NULL) /* Not actually mapped anymore */ goto out; for_each_process (tsk) { if (!task_early_kill(tsk)) continue; list_for_each_entry (vma, &av->head, anon_vma_node) { if (!page_mapped_in_vma(page, vma)) continue; if (vma->vm_mm == tsk->mm) add_to_kill(tsk, page, vma, to_kill, tkc); } } page_unlock_anon_vma(av); out: read_unlock(&tasklist_lock); } /* * Collect processes when the error hit a file mapped page. */ static void collect_procs_file(struct page *page, struct list_head *to_kill, struct to_kill **tkc) { struct vm_area_struct *vma; struct task_struct *tsk; struct prio_tree_iter iter; struct address_space *mapping = page->mapping; /* * A note on the locking order between the two locks. * We don't rely on this particular order. * If you have some other code that needs a different order * feel free to switch them around. Or add a reverse link * from mm_struct to task_struct, then this could be all * done without taking tasklist_lock and looping over all tasks. */ read_lock(&tasklist_lock); spin_lock(&mapping->i_mmap_lock); for_each_process(tsk) { pgoff_t pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT); if (!task_early_kill(tsk)) continue; vma_prio_tree_foreach(vma, &iter, &mapping->i_mmap, pgoff, pgoff) { /* * Send early kill signal to tasks where a vma covers * the page but the corrupted page is not necessarily * mapped it in its pte. * Assume applications who requested early kill want * to be informed of all such data corruptions. */ if (vma->vm_mm == tsk->mm) add_to_kill(tsk, page, vma, to_kill, tkc); } } spin_unlock(&mapping->i_mmap_lock); read_unlock(&tasklist_lock); } /* * Collect the processes who have the corrupted page mapped to kill. * This is done in two steps for locking reasons. * First preallocate one tokill structure outside the spin locks, * so that we can kill at least one process reasonably reliable. */ static void collect_procs(struct page *page, struct list_head *tokill) { struct to_kill *tk; if (!page->mapping) return; tk = kmalloc(sizeof(struct to_kill), GFP_NOIO); if (!tk) return; if (PageAnon(page)) collect_procs_anon(page, tokill, &tk); else collect_procs_file(page, tokill, &tk); kfree(tk); } /* * Error handlers for various types of pages. */ enum outcome { IGNORED, /* Error: cannot be handled */ FAILED, /* Error: handling failed */ DELAYED, /* Will be handled later */ RECOVERED, /* Successfully recovered */ }; static const char *action_name[] = { [IGNORED] = "Ignored", [FAILED] = "Failed", [DELAYED] = "Delayed", [RECOVERED] = "Recovered", }; /* * XXX: It is possible that a page is isolated from LRU cache, * and then kept in swap cache or failed to remove from page cache. * The page count will stop it from being freed by unpoison. * Stress tests should be aware of this memory leak problem. */ static int delete_from_lru_cache(struct page *p) { if (!isolate_lru_page(p)) { /* * Clear sensible page flags, so that the buddy system won't * complain when the page is unpoison-and-freed. */ ClearPageActive(p); ClearPageUnevictable(p); /* * drop the page count elevated by isolate_lru_page() */ page_cache_release(p); return 0; } return -EIO; } /* * Error hit kernel page. * Do nothing, try to be lucky and not touch this instead. For a few cases we * could be more sophisticated. */ static int me_kernel(struct page *p, unsigned long pfn) { return IGNORED; } /* * Page in unknown state. Do nothing. */ static int me_unknown(struct page *p, unsigned long pfn) { printk(KERN_ERR "MCE %#lx: Unknown page state\n", pfn); return FAILED; } /* * Clean (or cleaned) page cache page. */ static int me_pagecache_clean(struct page *p, unsigned long pfn) { int err; int ret = FAILED; struct address_space *mapping; delete_from_lru_cache(p); /* * For anonymous pages we're done the only reference left * should be the one m_f() holds. */ if (PageAnon(p)) return RECOVERED; /* * Now truncate the page in the page cache. This is really * more like a "temporary hole punch" * Don't do this for block devices when someone else * has a reference, because it could be file system metadata * and that's not safe to truncate. */ mapping = page_mapping(p); if (!mapping) { /* * Page has been teared down in the meanwhile */ return FAILED; } /* * Truncation is a bit tricky. Enable it per file system for now. * * Open: to take i_mutex or not for this? Right now we don't. */ if (mapping->a_ops->error_remove_page) { err = mapping->a_ops->error_remove_page(mapping, p); if (err != 0) { printk(KERN_INFO "MCE %#lx: Failed to punch page: %d\n", pfn, err); } else if (page_has_private(p) && !try_to_release_page(p, GFP_NOIO)) { pr_debug("MCE %#lx: failed to release buffers\n", pfn); } else { ret = RECOVERED; } } else { /* * If the file system doesn't support it just invalidate * This fails on dirty or anything with private pages */ if (invalidate_inode_page(p)) ret = RECOVERED; else printk(KERN_INFO "MCE %#lx: Failed to invalidate\n", pfn); } return ret; } /* * Dirty cache page page * Issues: when the error hit a hole page the error is not properly * propagated. */ static int me_pagecache_dirty(struct page *p, unsigned long pfn) { struct address_space *mapping = page_mapping(p); SetPageError(p); /* TBD: print more information about the file. */ if (mapping) { /* * IO error will be reported by write(), fsync(), etc. * who check the mapping. * This way the application knows that something went * wrong with its dirty file data. * * There's one open issue: * * The EIO will be only reported on the next IO * operation and then cleared through the IO map. * Normally Linux has two mechanisms to pass IO error * first through the AS_EIO flag in the address space * and then through the PageError flag in the page. * Since we drop pages on memory failure handling the * only mechanism open to use is through AS_AIO. * * This has the disadvantage that it gets cleared on * the first operation that returns an error, while * the PageError bit is more sticky and only cleared * when the page is reread or dropped. If an * application assumes it will always get error on * fsync, but does other operations on the fd before * and the page is dropped inbetween then the error * will not be properly reported. * * This can already happen even without hwpoisoned * pages: first on metadata IO errors (which only * report through AS_EIO) or when the page is dropped * at the wrong time. * * So right now we assume that the application DTRT on * the first EIO, but we're not worse than other parts * of the kernel. */ mapping_set_error(mapping, EIO); } return me_pagecache_clean(p, pfn); } /* * Clean and dirty swap cache. * * Dirty swap cache page is tricky to handle. The page could live both in page * cache and swap cache(ie. page is freshly swapped in). So it could be * referenced concurrently by 2 types of PTEs: * normal PTEs and swap PTEs. We try to handle them consistently by calling * try_to_unmap(TTU_IGNORE_HWPOISON) to convert the normal PTEs to swap PTEs, * and then * - clear dirty bit to prevent IO * - remove from LRU * - but keep in the swap cache, so that when we return to it on * a later page fault, we know the application is accessing * corrupted data and shall be killed (we installed simple * interception code in do_swap_page to catch it). * * Clean swap cache pages can be directly isolated. A later page fault will * bring in the known good data from disk. */ static int me_swapcache_dirty(struct page *p, unsigned long pfn) { ClearPageDirty(p); /* Trigger EIO in shmem: */ ClearPageUptodate(p); if (!delete_from_lru_cache(p)) return DELAYED; else return FAILED; } static int me_swapcache_clean(struct page *p, unsigned long pfn) { delete_from_swap_cache(p); if (!delete_from_lru_cache(p)) return RECOVERED; else return FAILED; } /* * Huge pages. Needs work. * Issues: * No rmap support so we cannot find the original mapper. In theory could walk * all MMs and look for the mappings, but that would be non atomic and racy. * Need rmap for hugepages for this. Alternatively we could employ a heuristic, * like just walking the current process and hoping it has it mapped (that * should be usually true for the common "shared database cache" case) * Should handle free huge pages and dequeue them too, but this needs to * handle huge page accounting correctly. */ static int me_huge_page(struct page *p, unsigned long pfn) { return FAILED; } /* * Various page states we can handle. * * A page state is defined by its current page->flags bits. * The table matches them in order and calls the right handler. * * This is quite tricky because we can access page at any time * in its live cycle, so all accesses have to be extremly careful. * * This is not complete. More states could be added. * For any missing state don't attempt recovery. */ #define dirty (1UL << PG_dirty) #define sc (1UL << PG_swapcache) #define unevict (1UL << PG_unevictable) #define mlock (1UL << PG_mlocked) #define writeback (1UL << PG_writeback) #define lru (1UL << PG_lru) #define swapbacked (1UL << PG_swapbacked) #define head (1UL << PG_head) #define tail (1UL << PG_tail) #define compound (1UL << PG_compound) #define slab (1UL << PG_slab) #define reserved (1UL << PG_reserved) static struct page_state { unsigned long mask; unsigned long res; char *msg; int (*action)(struct page *p, unsigned long pfn); } error_states[] = { { reserved, reserved, "reserved kernel", me_kernel }, /* * free pages are specially detected outside this table: * PG_buddy pages only make a small fraction of all free pages. */ /* * Could in theory check if slab page is free or if we can drop * currently unused objects without touching them. But just * treat it as standard kernel for now. */ { slab, slab, "kernel slab", me_kernel }, #ifdef CONFIG_PAGEFLAGS_EXTENDED { head, head, "huge", me_huge_page }, { tail, tail, "huge", me_huge_page }, #else { compound, compound, "huge", me_huge_page }, #endif { sc|dirty, sc|dirty, "swapcache", me_swapcache_dirty }, { sc|dirty, sc, "swapcache", me_swapcache_clean }, { unevict|dirty, unevict|dirty, "unevictable LRU", me_pagecache_dirty}, { unevict, unevict, "unevictable LRU", me_pagecache_clean}, { mlock|dirty, mlock|dirty, "mlocked LRU", me_pagecache_dirty }, { mlock, mlock, "mlocked LRU", me_pagecache_clean }, { lru|dirty, lru|dirty, "LRU", me_pagecache_dirty }, { lru|dirty, lru, "clean LRU", me_pagecache_clean }, /* * Catchall entry: must be at end. */ { 0, 0, "unknown page state", me_unknown }, }; #undef dirty #undef sc #undef unevict #undef mlock #undef writeback #undef lru #undef swapbacked #undef head #undef tail #undef compound #undef slab #undef reserved static void action_result(unsigned long pfn, char *msg, int result) { struct page *page = pfn_to_page(pfn); printk(KERN_ERR "MCE %#lx: %s%s page recovery: %s\n", pfn, PageDirty(page) ? "dirty " : "", msg, action_name[result]); } static int page_action(struct page_state *ps, struct page *p, unsigned long pfn) { int result; int count; result = ps->action(p, pfn); action_result(pfn, ps->msg, result); count = page_count(p) - 1; if (ps->action == me_swapcache_dirty && result == DELAYED) count--; if (count != 0) { printk(KERN_ERR "MCE %#lx: %s page still referenced by %d users\n", pfn, ps->msg, count); result = FAILED; } /* Could do more checks here if page looks ok */ /* * Could adjust zone counters here to correct for the missing page. */ return (result == RECOVERED || result == DELAYED) ? 0 : -EBUSY; } #define N_UNMAP_TRIES 5 /* * Do all that is necessary to remove user space mappings. Unmap * the pages and send SIGBUS to the processes if the data was dirty. */ static int hwpoison_user_mappings(struct page *p, unsigned long pfn, int trapno) { enum ttu_flags ttu = TTU_UNMAP | TTU_IGNORE_MLOCK | TTU_IGNORE_ACCESS; struct address_space *mapping; LIST_HEAD(tokill); int ret; int i; int kill = 1; if (PageReserved(p) || PageSlab(p)) return SWAP_SUCCESS; /* * This check implies we don't kill processes if their pages * are in the swap cache early. Those are always late kills. */ if (!page_mapped(p)) return SWAP_SUCCESS; if (PageCompound(p) || PageKsm(p)) return SWAP_FAIL; if (PageSwapCache(p)) { printk(KERN_ERR "MCE %#lx: keeping poisoned page in swap cache\n", pfn); ttu |= TTU_IGNORE_HWPOISON; } /* * Propagate the dirty bit from PTEs to struct page first, because we * need this to decide if we should kill or just drop the page. * XXX: the dirty test could be racy: set_page_dirty() may not always * be called inside page lock (it's recommended but not enforced). */ mapping = page_mapping(p); if (!PageDirty(p) && mapping && mapping_cap_writeback_dirty(mapping)) { if (page_mkclean(p)) { SetPageDirty(p); } else { kill = 0; ttu |= TTU_IGNORE_HWPOISON; printk(KERN_INFO "MCE %#lx: corrupted page was clean: dropped without side effects\n", pfn); } } /* * First collect all the processes that have the page * mapped in dirty form. This has to be done before try_to_unmap, * because ttu takes the rmap data structures down. * * Error handling: We ignore errors here because * there's nothing that can be done. */ if (kill) collect_procs(p, &tokill); /* * try_to_unmap can fail temporarily due to races. * Try a few times (RED-PEN better strategy?) */ for (i = 0; i < N_UNMAP_TRIES; i++) { ret = try_to_unmap(p, ttu); if (ret == SWAP_SUCCESS) break; pr_debug("MCE %#lx: try_to_unmap retry needed %d\n", pfn, ret); } if (ret != SWAP_SUCCESS) printk(KERN_ERR "MCE %#lx: failed to unmap page (mapcount=%d)\n", pfn, page_mapcount(p)); /* * Now that the dirty bit has been propagated to the * struct page and all unmaps done we can decide if * killing is needed or not. Only kill when the page * was dirty, otherwise the tokill list is merely * freed. When there was a problem unmapping earlier * use a more force-full uncatchable kill to prevent * any accesses to the poisoned memory. */ kill_procs_ao(&tokill, !!PageDirty(p), trapno, ret != SWAP_SUCCESS, pfn); return ret; } int __memory_failure(unsigned long pfn, int trapno, int flags) { struct page_state *ps; struct page *p; int res; if (!sysctl_memory_failure_recovery) panic("Memory failure from trap %d on page %lx", trapno, pfn); if (!pfn_valid(pfn)) { printk(KERN_ERR "MCE %#lx: memory outside kernel control\n", pfn); return -ENXIO; } p = pfn_to_page(pfn); if (TestSetPageHWPoison(p)) { printk(KERN_ERR "MCE %#lx: already hardware poisoned\n", pfn); return 0; } atomic_long_add(1, &mce_bad_pages); /* * We need/can do nothing about count=0 pages. * 1) it's a free page, and therefore in safe hand: * prep_new_page() will be the gate keeper. * 2) it's part of a non-compound high order page. * Implies some kernel user: cannot stop them from * R/W the page; let's pray that the page has been * used and will be freed some time later. * In fact it's dangerous to directly bump up page count from 0, * that may make page_freeze_refs()/page_unfreeze_refs() mismatch. */ if (!(flags & MF_COUNT_INCREASED) && !get_page_unless_zero(compound_head(p))) { if (is_free_buddy_page(p)) { action_result(pfn, "free buddy", DELAYED); return 0; } else { action_result(pfn, "high order kernel", IGNORED); return -EBUSY; } } /* * We ignore non-LRU pages for good reasons. * - PG_locked is only well defined for LRU pages and a few others * - to avoid races with __set_page_locked() * - to avoid races with __SetPageSlab*() (and more non-atomic ops) * The check (unnecessarily) ignores LRU pages being isolated and * walked by the page reclaim code, however that's not a big loss. */ if (!PageLRU(p)) shake_page(p, 0); if (!PageLRU(p)) { /* * shake_page could have turned it free. */ if (is_free_buddy_page(p)) { action_result(pfn, "free buddy, 2nd try", DELAYED); return 0; } action_result(pfn, "non LRU", IGNORED); put_page(p); return -EBUSY; } /* * Lock the page and wait for writeback to finish. * It's very difficult to mess with pages currently under IO * and in many cases impossible, so we just avoid it here. */ lock_page_nosync(p); /* * unpoison always clear PG_hwpoison inside page lock */ if (!PageHWPoison(p)) { printk(KERN_ERR "MCE %#lx: just unpoisoned\n", pfn); res = 0; goto out; } if (hwpoison_filter(p)) { if (TestClearPageHWPoison(p)) atomic_long_dec(&mce_bad_pages); unlock_page(p); put_page(p); return 0; } wait_on_page_writeback(p); /* * Now take care of user space mappings. * Abort on fail: __remove_from_page_cache() assumes unmapped page. */ if (hwpoison_user_mappings(p, pfn, trapno) != SWAP_SUCCESS) { printk(KERN_ERR "MCE %#lx: cannot unmap page, give up\n", pfn); res = -EBUSY; goto out; } /* * Torn down by someone else? */ if (PageLRU(p) && !PageSwapCache(p) && p->mapping == NULL) { action_result(pfn, "already truncated LRU", IGNORED); res = -EBUSY; goto out; } res = -EBUSY; for (ps = error_states;; ps++) { if ((p->flags & ps->mask) == ps->res) { res = page_action(ps, p, pfn); break; } } out: unlock_page(p); return res; } EXPORT_SYMBOL_GPL(__memory_failure); /** * memory_failure - Handle memory failure of a page. * @pfn: Page Number of the corrupted page * @trapno: Trap number reported in the signal to user space. * * This function is called by the low level machine check code * of an architecture when it detects hardware memory corruption * of a page. It tries its best to recover, which includes * dropping pages, killing processes etc. * * The function is primarily of use for corruptions that * happen outside the current execution context (e.g. when * detected by a background scrubber) * * Must run in process context (e.g. a work queue) with interrupts * enabled and no spinlocks hold. */ void memory_failure(unsigned long pfn, int trapno) { __memory_failure(pfn, trapno, 0); } /** * unpoison_memory - Unpoison a previously poisoned page * @pfn: Page number of the to be unpoisoned page * * Software-unpoison a page that has been poisoned by * memory_failure() earlier. * * This is only done on the software-level, so it only works * for linux injected failures, not real hardware failures * * Returns 0 for success, otherwise -errno. */ int unpoison_memory(unsigned long pfn) { struct page *page; struct page *p; int freeit = 0; if (!pfn_valid(pfn)) return -ENXIO; p = pfn_to_page(pfn); page = compound_head(p); if (!PageHWPoison(p)) { pr_debug("MCE: Page was already unpoisoned %#lx\n", pfn); return 0; } if (!get_page_unless_zero(page)) { if (TestClearPageHWPoison(p)) atomic_long_dec(&mce_bad_pages); pr_debug("MCE: Software-unpoisoned free page %#lx\n", pfn); return 0; } lock_page_nosync(page); /* * This test is racy because PG_hwpoison is set outside of page lock. * That's acceptable because that won't trigger kernel panic. Instead, * the PG_hwpoison page will be caught and isolated on the entrance to * the free buddy page pool. */ if (TestClearPageHWPoison(p)) { pr_debug("MCE: Software-unpoisoned page %#lx\n", pfn); atomic_long_dec(&mce_bad_pages); freeit = 1; } unlock_page(page); put_page(page); if (freeit) put_page(page); return 0; } EXPORT_SYMBOL(unpoison_memory); static struct page *new_page(struct page *p, unsigned long private, int **x) { int nid = page_to_nid(p); return alloc_pages_exact_node(nid, GFP_HIGHUSER_MOVABLE, 0); } /* * Safely get reference count of an arbitrary page. * Returns 0 for a free page, -EIO for a zero refcount page * that is not free, and 1 for any other page type. * For 1 the page is returned with increased page count, otherwise not. */ static int get_any_page(struct page *p, unsigned long pfn, int flags) { int ret; if (flags & MF_COUNT_INCREASED) return 1; /* * The lock_system_sleep prevents a race with memory hotplug, * because the isolation assumes there's only a single user. * This is a big hammer, a better would be nicer. */ lock_system_sleep(); /* * Isolate the page, so that it doesn't get reallocated if it * was free. */ set_migratetype_isolate(p); if (!get_page_unless_zero(compound_head(p))) { if (is_free_buddy_page(p)) { pr_debug("get_any_page: %#lx free buddy page\n", pfn); /* Set hwpoison bit while page is still isolated */ SetPageHWPoison(p); ret = 0; } else { pr_debug("get_any_page: %#lx: unknown zero refcount page type %lx\n", pfn, p->flags); ret = -EIO; } } else { /* Not a free page */ ret = 1; } unset_migratetype_isolate(p); unlock_system_sleep(); return ret; } /** * soft_offline_page - Soft offline a page. * @page: page to offline * @flags: flags. Same as memory_failure(). * * Returns 0 on success, otherwise negated errno. * * Soft offline a page, by migration or invalidation, * without killing anything. This is for the case when * a page is not corrupted yet (so it's still valid to access), * but has had a number of corrected errors and is better taken * out. * * The actual policy on when to do that is maintained by * user space. * * This should never impact any application or cause data loss, * however it might take some time. * * This is not a 100% solution for all memory, but tries to be * ``good enough'' for the majority of memory. */ int soft_offline_page(struct page *page, int flags) { int ret; unsigned long pfn = page_to_pfn(page); ret = get_any_page(page, pfn, flags); if (ret < 0) return ret; if (ret == 0) goto done; /* * Page cache page we can handle? */ if (!PageLRU(page)) { /* * Try to free it. */ put_page(page); shake_page(page, 1); /* * Did it turn free? */ ret = get_any_page(page, pfn, 0); if (ret < 0) return ret; if (ret == 0) goto done; } if (!PageLRU(page)) { pr_debug("soft_offline: %#lx: unknown non LRU page type %lx\n", pfn, page->flags); return -EIO; } lock_page(page); wait_on_page_writeback(page); /* * Synchronized using the page lock with memory_failure() */ if (PageHWPoison(page)) { unlock_page(page); put_page(page); pr_debug("soft offline: %#lx page already poisoned\n", pfn); return -EBUSY; } /* * Try to invalidate first. This should work for * non dirty unmapped page cache pages. */ ret = invalidate_inode_page(page); unlock_page(page); /* * Drop count because page migration doesn't like raised * counts. The page could get re-allocated, but if it becomes * LRU the isolation will just fail. * RED-PEN would be better to keep it isolated here, but we * would need to fix isolation locking first. */ put_page(page); if (ret == 1) { ret = 0; pr_debug("soft_offline: %#lx: invalidated\n", pfn); goto done; } /* * Simple invalidation didn't work. * Try to migrate to a new page instead. migrate.c * handles a large number of cases for us. */ ret = isolate_lru_page(page); if (!ret) { LIST_HEAD(pagelist); list_add(&page->lru, &pagelist); ret = migrate_pages(&pagelist, new_page, MPOL_MF_MOVE_ALL, 0); if (ret) { pr_debug("soft offline: %#lx: migration failed %d, type %lx\n", pfn, ret, page->flags); if (ret > 0) ret = -EIO; } } else { pr_debug("soft offline: %#lx: isolation failed: %d, page count %d, type %lx\n", pfn, ret, page_count(page), page->flags); } if (ret) return ret; done: atomic_long_add(1, &mce_bad_pages); SetPageHWPoison(page); /* keep elevated page count for bad page */ return ret; }