/*
* 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/sched.h>
#include <linux/rmap.h>
#include <linux/pagemap.h>
#include <linux/swap.h>
#include <linux/backing-dev.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);
/*
* 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;
}
/*
* 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 munmaping
* make sure the process doesn't catch the
* signal and then access the memory. Just kill it.
* the signal handlers
*/
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 {
FAILED, /* Error handling failed */
DELAYED, /* Will be handled later */
IGNORED, /* Error safely ignored */
RECOVERED, /* Successfully recovered */
};
static const char *action_name[] = {
[FAILED] = "Failed",
[DELAYED] = "Delayed",
[IGNORED] = "Ignored",
[RECOVERED] = "Recovered",
};
/*
* 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 DELAYED;
}
/*
* Already poisoned page.
*/
static int me_ignore(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;
}
/*
* Free memory
*/
static int me_free(struct page *p, unsigned long pfn)
{
return DELAYED;
}
/*
* 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;
/*
* 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);
return DELAYED;
}
static int me_swapcache_clean(struct page *p, unsigned long pfn)
{
delete_from_swap_cache(p);
return RECOVERED;
}
/*
* 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 buddy (1UL << PG_buddy)
#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_ignore },
{ buddy, buddy, "free kernel", me_free },
/*
* 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},
#ifdef CONFIG_HAVE_MLOCKED_PAGE_BIT
{ mlock|dirty, mlock|dirty, "mlocked LRU", me_pagecache_dirty },
{ mlock, mlock, "mlocked LRU", me_pagecache_clean },
#endif
{ lru|dirty, lru|dirty, "LRU", me_pagecache_dirty },
{ lru|dirty, lru, "clean LRU", me_pagecache_clean },
{ swapbacked, swapbacked, "anonymous", me_pagecache_clean },
/*
* Catchall entry: must be at end.
*/
{ 0, 0, "unknown page state", me_unknown },
};
static void action_result(unsigned long pfn, char *msg, int result)
{
struct page *page = NULL;
if (pfn_valid(pfn))
page = pfn_to_page(pfn);
printk(KERN_ERR "MCE %#lx: %s%s page recovery: %s\n",
pfn,
page && PageDirty(page) ? "dirty " : "",
msg, action_name[result]);
}
static int page_action(struct page_state *ps, struct page *p,
unsigned long pfn, int ref)
{
int result;
result = ps->action(p, pfn);
action_result(pfn, ps->msg, result);
if (page_count(p) != 1 + ref)
printk(KERN_ERR
"MCE %#lx: %s page still referenced by %d users\n",
pfn, ps->msg, page_count(p) - 1);
/* Could do more checks here if page looks ok */
/*
* Could adjust zone counters here to correct for the missing page.
*/
return result == RECOVERED ? 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 void 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) || PageCompound(p) || PageSlab(p))
return;
/*
* 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;
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.
*/
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);
}
int __memory_failure(unsigned long pfn, int trapno, int ref)
{
unsigned long lru_flag;
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)) {
action_result(pfn, "memory outside kernel control", IGNORED);
return -EIO;
}
p = pfn_to_page(pfn);
if (TestSetPageHWPoison(p)) {
action_result(pfn, "already hardware poisoned", IGNORED);
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 (!get_page_unless_zero(compound_head(p))) {
action_result(pfn, "free or high order kernel", IGNORED);
return PageBuddy(compound_head(p)) ? 0 : -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))
lru_add_drain_all();
lru_flag = p->flags & lru;
if (isolate_lru_page(p)) {
action_result(pfn, "non LRU", IGNORED);
put_page(p);
return -EBUSY;
}
page_cache_release(p);
/*
* 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);
wait_on_page_writeback(p);
/*
* Now take care of user space mappings.
*/
hwpoison_user_mappings(p, pfn, trapno);
/*
* Torn down by someone else?
*/
if ((lru_flag & lru) && !PageSwapCache(p) && p->mapping == NULL) {
action_result(pfn, "already truncated LRU", IGNORED);
res = 0;
goto out;
}
res = -EBUSY;
for (ps = error_states;; ps++) {
if (((p->flags | lru_flag)& ps->mask) == ps->res) {
res = page_action(ps, p, pfn, ref);
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);
}
