kernel-ark/mm/oom_kill.c
Wang Nan 687cb0884a mm, oom_reaper: gather each vma to prevent leaking TLB entry
tlb_gather_mmu(&tlb, mm, 0, -1) means gathering the whole virtual memory
space.  In this case, tlb->fullmm is true.  Some archs like arm64
doesn't flush TLB when tlb->fullmm is true:

  commit 5a7862e830 ("arm64: tlbflush: avoid flushing when fullmm == 1").

Which causes leaking of tlb entries.

Will clarifies his patch:
 "Basically, we tag each address space with an ASID (PCID on x86) which
  is resident in the TLB. This means we can elide TLB invalidation when
  pulling down a full mm because we won't ever assign that ASID to
  another mm without doing TLB invalidation elsewhere (which actually
  just nukes the whole TLB).

  I think that means that we could potentially not fault on a kernel
  uaccess, because we could hit in the TLB"

There could be a window between complete_signal() sending IPI to other
cores and all threads sharing this mm are really kicked off from cores.
In this window, the oom reaper may calls tlb_flush_mmu_tlbonly() to
flush TLB then frees pages.  However, due to the above problem, the TLB
entries are not really flushed on arm64.  Other threads are possible to
access these pages through TLB entries.  Moreover, a copy_to_user() can
also write to these pages without generating page fault, causes
use-after-free bugs.

This patch gathers each vma instead of gathering full vm space.  In this
case tlb->fullmm is not true.  The behavior of oom reaper become similar
to munmapping before do_exit, which should be safe for all archs.

Link: http://lkml.kernel.org/r/20171107095453.179940-1-wangnan0@huawei.com
Fixes: aac4536355 ("mm, oom: introduce oom reaper")
Signed-off-by: Wang Nan <wangnan0@huawei.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Acked-by: David Rientjes <rientjes@google.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Bob Liu <liubo95@huawei.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Roman Gushchin <guro@fb.com>
Cc: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2017-11-29 18:40:42 -08:00

1111 lines
30 KiB
C

/*
* linux/mm/oom_kill.c
*
* Copyright (C) 1998,2000 Rik van Riel
* Thanks go out to Claus Fischer for some serious inspiration and
* for goading me into coding this file...
* Copyright (C) 2010 Google, Inc.
* Rewritten by David Rientjes
*
* The routines in this file are used to kill a process when
* we're seriously out of memory. This gets called from __alloc_pages()
* in mm/page_alloc.c when we really run out of memory.
*
* Since we won't call these routines often (on a well-configured
* machine) this file will double as a 'coding guide' and a signpost
* for newbie kernel hackers. It features several pointers to major
* kernel subsystems and hints as to where to find out what things do.
*/
#include <linux/oom.h>
#include <linux/mm.h>
#include <linux/err.h>
#include <linux/gfp.h>
#include <linux/sched.h>
#include <linux/sched/mm.h>
#include <linux/sched/coredump.h>
#include <linux/sched/task.h>
#include <linux/swap.h>
#include <linux/timex.h>
#include <linux/jiffies.h>
#include <linux/cpuset.h>
#include <linux/export.h>
#include <linux/notifier.h>
#include <linux/memcontrol.h>
#include <linux/mempolicy.h>
#include <linux/security.h>
#include <linux/ptrace.h>
#include <linux/freezer.h>
#include <linux/ftrace.h>
#include <linux/ratelimit.h>
#include <linux/kthread.h>
#include <linux/init.h>
#include <linux/mmu_notifier.h>
#include <asm/tlb.h>
#include "internal.h"
#include "slab.h"
#define CREATE_TRACE_POINTS
#include <trace/events/oom.h>
int sysctl_panic_on_oom;
int sysctl_oom_kill_allocating_task;
int sysctl_oom_dump_tasks = 1;
DEFINE_MUTEX(oom_lock);
#ifdef CONFIG_NUMA
/**
* has_intersects_mems_allowed() - check task eligiblity for kill
* @start: task struct of which task to consider
* @mask: nodemask passed to page allocator for mempolicy ooms
*
* Task eligibility is determined by whether or not a candidate task, @tsk,
* shares the same mempolicy nodes as current if it is bound by such a policy
* and whether or not it has the same set of allowed cpuset nodes.
*/
static bool has_intersects_mems_allowed(struct task_struct *start,
const nodemask_t *mask)
{
struct task_struct *tsk;
bool ret = false;
rcu_read_lock();
for_each_thread(start, tsk) {
if (mask) {
/*
* If this is a mempolicy constrained oom, tsk's
* cpuset is irrelevant. Only return true if its
* mempolicy intersects current, otherwise it may be
* needlessly killed.
*/
ret = mempolicy_nodemask_intersects(tsk, mask);
} else {
/*
* This is not a mempolicy constrained oom, so only
* check the mems of tsk's cpuset.
*/
ret = cpuset_mems_allowed_intersects(current, tsk);
}
if (ret)
break;
}
rcu_read_unlock();
return ret;
}
#else
static bool has_intersects_mems_allowed(struct task_struct *tsk,
const nodemask_t *mask)
{
return true;
}
#endif /* CONFIG_NUMA */
/*
* The process p may have detached its own ->mm while exiting or through
* use_mm(), but one or more of its subthreads may still have a valid
* pointer. Return p, or any of its subthreads with a valid ->mm, with
* task_lock() held.
*/
struct task_struct *find_lock_task_mm(struct task_struct *p)
{
struct task_struct *t;
rcu_read_lock();
for_each_thread(p, t) {
task_lock(t);
if (likely(t->mm))
goto found;
task_unlock(t);
}
t = NULL;
found:
rcu_read_unlock();
return t;
}
/*
* order == -1 means the oom kill is required by sysrq, otherwise only
* for display purposes.
*/
static inline bool is_sysrq_oom(struct oom_control *oc)
{
return oc->order == -1;
}
static inline bool is_memcg_oom(struct oom_control *oc)
{
return oc->memcg != NULL;
}
/* return true if the task is not adequate as candidate victim task. */
static bool oom_unkillable_task(struct task_struct *p,
struct mem_cgroup *memcg, const nodemask_t *nodemask)
{
if (is_global_init(p))
return true;
if (p->flags & PF_KTHREAD)
return true;
/* When mem_cgroup_out_of_memory() and p is not member of the group */
if (memcg && !task_in_mem_cgroup(p, memcg))
return true;
/* p may not have freeable memory in nodemask */
if (!has_intersects_mems_allowed(p, nodemask))
return true;
return false;
}
/*
* Print out unreclaimble slabs info when unreclaimable slabs amount is greater
* than all user memory (LRU pages)
*/
static bool is_dump_unreclaim_slabs(void)
{
unsigned long nr_lru;
nr_lru = global_node_page_state(NR_ACTIVE_ANON) +
global_node_page_state(NR_INACTIVE_ANON) +
global_node_page_state(NR_ACTIVE_FILE) +
global_node_page_state(NR_INACTIVE_FILE) +
global_node_page_state(NR_ISOLATED_ANON) +
global_node_page_state(NR_ISOLATED_FILE) +
global_node_page_state(NR_UNEVICTABLE);
return (global_node_page_state(NR_SLAB_UNRECLAIMABLE) > nr_lru);
}
/**
* oom_badness - heuristic function to determine which candidate task to kill
* @p: task struct of which task we should calculate
* @totalpages: total present RAM allowed for page allocation
*
* The heuristic for determining which task to kill is made to be as simple and
* predictable as possible. The goal is to return the highest value for the
* task consuming the most memory to avoid subsequent oom failures.
*/
unsigned long oom_badness(struct task_struct *p, struct mem_cgroup *memcg,
const nodemask_t *nodemask, unsigned long totalpages)
{
long points;
long adj;
if (oom_unkillable_task(p, memcg, nodemask))
return 0;
p = find_lock_task_mm(p);
if (!p)
return 0;
/*
* Do not even consider tasks which are explicitly marked oom
* unkillable or have been already oom reaped or the are in
* the middle of vfork
*/
adj = (long)p->signal->oom_score_adj;
if (adj == OOM_SCORE_ADJ_MIN ||
test_bit(MMF_OOM_SKIP, &p->mm->flags) ||
in_vfork(p)) {
task_unlock(p);
return 0;
}
/*
* The baseline for the badness score is the proportion of RAM that each
* task's rss, pagetable and swap space use.
*/
points = get_mm_rss(p->mm) + get_mm_counter(p->mm, MM_SWAPENTS) +
mm_pgtables_bytes(p->mm) / PAGE_SIZE;
task_unlock(p);
/*
* Root processes get 3% bonus, just like the __vm_enough_memory()
* implementation used by LSMs.
*/
if (has_capability_noaudit(p, CAP_SYS_ADMIN))
points -= (points * 3) / 100;
/* Normalize to oom_score_adj units */
adj *= totalpages / 1000;
points += adj;
/*
* Never return 0 for an eligible task regardless of the root bonus and
* oom_score_adj (oom_score_adj can't be OOM_SCORE_ADJ_MIN here).
*/
return points > 0 ? points : 1;
}
enum oom_constraint {
CONSTRAINT_NONE,
CONSTRAINT_CPUSET,
CONSTRAINT_MEMORY_POLICY,
CONSTRAINT_MEMCG,
};
/*
* Determine the type of allocation constraint.
*/
static enum oom_constraint constrained_alloc(struct oom_control *oc)
{
struct zone *zone;
struct zoneref *z;
enum zone_type high_zoneidx = gfp_zone(oc->gfp_mask);
bool cpuset_limited = false;
int nid;
if (is_memcg_oom(oc)) {
oc->totalpages = mem_cgroup_get_limit(oc->memcg) ?: 1;
return CONSTRAINT_MEMCG;
}
/* Default to all available memory */
oc->totalpages = totalram_pages + total_swap_pages;
if (!IS_ENABLED(CONFIG_NUMA))
return CONSTRAINT_NONE;
if (!oc->zonelist)
return CONSTRAINT_NONE;
/*
* Reach here only when __GFP_NOFAIL is used. So, we should avoid
* to kill current.We have to random task kill in this case.
* Hopefully, CONSTRAINT_THISNODE...but no way to handle it, now.
*/
if (oc->gfp_mask & __GFP_THISNODE)
return CONSTRAINT_NONE;
/*
* This is not a __GFP_THISNODE allocation, so a truncated nodemask in
* the page allocator means a mempolicy is in effect. Cpuset policy
* is enforced in get_page_from_freelist().
*/
if (oc->nodemask &&
!nodes_subset(node_states[N_MEMORY], *oc->nodemask)) {
oc->totalpages = total_swap_pages;
for_each_node_mask(nid, *oc->nodemask)
oc->totalpages += node_spanned_pages(nid);
return CONSTRAINT_MEMORY_POLICY;
}
/* Check this allocation failure is caused by cpuset's wall function */
for_each_zone_zonelist_nodemask(zone, z, oc->zonelist,
high_zoneidx, oc->nodemask)
if (!cpuset_zone_allowed(zone, oc->gfp_mask))
cpuset_limited = true;
if (cpuset_limited) {
oc->totalpages = total_swap_pages;
for_each_node_mask(nid, cpuset_current_mems_allowed)
oc->totalpages += node_spanned_pages(nid);
return CONSTRAINT_CPUSET;
}
return CONSTRAINT_NONE;
}
static int oom_evaluate_task(struct task_struct *task, void *arg)
{
struct oom_control *oc = arg;
unsigned long points;
if (oom_unkillable_task(task, NULL, oc->nodemask))
goto next;
/*
* This task already has access to memory reserves and is being killed.
* Don't allow any other task to have access to the reserves unless
* the task has MMF_OOM_SKIP because chances that it would release
* any memory is quite low.
*/
if (!is_sysrq_oom(oc) && tsk_is_oom_victim(task)) {
if (test_bit(MMF_OOM_SKIP, &task->signal->oom_mm->flags))
goto next;
goto abort;
}
/*
* If task is allocating a lot of memory and has been marked to be
* killed first if it triggers an oom, then select it.
*/
if (oom_task_origin(task)) {
points = ULONG_MAX;
goto select;
}
points = oom_badness(task, NULL, oc->nodemask, oc->totalpages);
if (!points || points < oc->chosen_points)
goto next;
/* Prefer thread group leaders for display purposes */
if (points == oc->chosen_points && thread_group_leader(oc->chosen))
goto next;
select:
if (oc->chosen)
put_task_struct(oc->chosen);
get_task_struct(task);
oc->chosen = task;
oc->chosen_points = points;
next:
return 0;
abort:
if (oc->chosen)
put_task_struct(oc->chosen);
oc->chosen = (void *)-1UL;
return 1;
}
/*
* Simple selection loop. We choose the process with the highest number of
* 'points'. In case scan was aborted, oc->chosen is set to -1.
*/
static void select_bad_process(struct oom_control *oc)
{
if (is_memcg_oom(oc))
mem_cgroup_scan_tasks(oc->memcg, oom_evaluate_task, oc);
else {
struct task_struct *p;
rcu_read_lock();
for_each_process(p)
if (oom_evaluate_task(p, oc))
break;
rcu_read_unlock();
}
oc->chosen_points = oc->chosen_points * 1000 / oc->totalpages;
}
/**
* dump_tasks - dump current memory state of all system tasks
* @memcg: current's memory controller, if constrained
* @nodemask: nodemask passed to page allocator for mempolicy ooms
*
* Dumps the current memory state of all eligible tasks. Tasks not in the same
* memcg, not in the same cpuset, or bound to a disjoint set of mempolicy nodes
* are not shown.
* State information includes task's pid, uid, tgid, vm size, rss,
* pgtables_bytes, swapents, oom_score_adj value, and name.
*/
static void dump_tasks(struct mem_cgroup *memcg, const nodemask_t *nodemask)
{
struct task_struct *p;
struct task_struct *task;
pr_info("[ pid ] uid tgid total_vm rss pgtables_bytes swapents oom_score_adj name\n");
rcu_read_lock();
for_each_process(p) {
if (oom_unkillable_task(p, memcg, nodemask))
continue;
task = find_lock_task_mm(p);
if (!task) {
/*
* This is a kthread or all of p's threads have already
* detached their mm's. There's no need to report
* them; they can't be oom killed anyway.
*/
continue;
}
pr_info("[%5d] %5d %5d %8lu %8lu %8ld %8lu %5hd %s\n",
task->pid, from_kuid(&init_user_ns, task_uid(task)),
task->tgid, task->mm->total_vm, get_mm_rss(task->mm),
mm_pgtables_bytes(task->mm),
get_mm_counter(task->mm, MM_SWAPENTS),
task->signal->oom_score_adj, task->comm);
task_unlock(task);
}
rcu_read_unlock();
}
static void dump_header(struct oom_control *oc, struct task_struct *p)
{
pr_warn("%s invoked oom-killer: gfp_mask=%#x(%pGg), nodemask=%*pbl, order=%d, oom_score_adj=%hd\n",
current->comm, oc->gfp_mask, &oc->gfp_mask,
nodemask_pr_args(oc->nodemask), oc->order,
current->signal->oom_score_adj);
if (!IS_ENABLED(CONFIG_COMPACTION) && oc->order)
pr_warn("COMPACTION is disabled!!!\n");
cpuset_print_current_mems_allowed();
dump_stack();
if (is_memcg_oom(oc))
mem_cgroup_print_oom_info(oc->memcg, p);
else {
show_mem(SHOW_MEM_FILTER_NODES, oc->nodemask);
if (is_dump_unreclaim_slabs())
dump_unreclaimable_slab();
}
if (sysctl_oom_dump_tasks)
dump_tasks(oc->memcg, oc->nodemask);
}
/*
* Number of OOM victims in flight
*/
static atomic_t oom_victims = ATOMIC_INIT(0);
static DECLARE_WAIT_QUEUE_HEAD(oom_victims_wait);
static bool oom_killer_disabled __read_mostly;
#define K(x) ((x) << (PAGE_SHIFT-10))
/*
* task->mm can be NULL if the task is the exited group leader. So to
* determine whether the task is using a particular mm, we examine all the
* task's threads: if one of those is using this mm then this task was also
* using it.
*/
bool process_shares_mm(struct task_struct *p, struct mm_struct *mm)
{
struct task_struct *t;
for_each_thread(p, t) {
struct mm_struct *t_mm = READ_ONCE(t->mm);
if (t_mm)
return t_mm == mm;
}
return false;
}
#ifdef CONFIG_MMU
/*
* OOM Reaper kernel thread which tries to reap the memory used by the OOM
* victim (if that is possible) to help the OOM killer to move on.
*/
static struct task_struct *oom_reaper_th;
static DECLARE_WAIT_QUEUE_HEAD(oom_reaper_wait);
static struct task_struct *oom_reaper_list;
static DEFINE_SPINLOCK(oom_reaper_lock);
static bool __oom_reap_task_mm(struct task_struct *tsk, struct mm_struct *mm)
{
struct mmu_gather tlb;
struct vm_area_struct *vma;
bool ret = true;
/*
* We have to make sure to not race with the victim exit path
* and cause premature new oom victim selection:
* __oom_reap_task_mm exit_mm
* mmget_not_zero
* mmput
* atomic_dec_and_test
* exit_oom_victim
* [...]
* out_of_memory
* select_bad_process
* # no TIF_MEMDIE task selects new victim
* unmap_page_range # frees some memory
*/
mutex_lock(&oom_lock);
if (!down_read_trylock(&mm->mmap_sem)) {
ret = false;
trace_skip_task_reaping(tsk->pid);
goto unlock_oom;
}
/*
* If the mm has notifiers then we would need to invalidate them around
* unmap_page_range and that is risky because notifiers can sleep and
* what they do is basically undeterministic. So let's have a short
* sleep to give the oom victim some more time.
* TODO: we really want to get rid of this ugly hack and make sure that
* notifiers cannot block for unbounded amount of time and add
* mmu_notifier_invalidate_range_{start,end} around unmap_page_range
*/
if (mm_has_notifiers(mm)) {
up_read(&mm->mmap_sem);
schedule_timeout_idle(HZ);
goto unlock_oom;
}
/*
* MMF_OOM_SKIP is set by exit_mmap when the OOM reaper can't
* work on the mm anymore. The check for MMF_OOM_SKIP must run
* under mmap_sem for reading because it serializes against the
* down_write();up_write() cycle in exit_mmap().
*/
if (test_bit(MMF_OOM_SKIP, &mm->flags)) {
up_read(&mm->mmap_sem);
trace_skip_task_reaping(tsk->pid);
goto unlock_oom;
}
trace_start_task_reaping(tsk->pid);
/*
* Tell all users of get_user/copy_from_user etc... that the content
* is no longer stable. No barriers really needed because unmapping
* should imply barriers already and the reader would hit a page fault
* if it stumbled over a reaped memory.
*/
set_bit(MMF_UNSTABLE, &mm->flags);
for (vma = mm->mmap ; vma; vma = vma->vm_next) {
if (!can_madv_dontneed_vma(vma))
continue;
/*
* Only anonymous pages have a good chance to be dropped
* without additional steps which we cannot afford as we
* are OOM already.
*
* We do not even care about fs backed pages because all
* which are reclaimable have already been reclaimed and
* we do not want to block exit_mmap by keeping mm ref
* count elevated without a good reason.
*/
if (vma_is_anonymous(vma) || !(vma->vm_flags & VM_SHARED)) {
tlb_gather_mmu(&tlb, mm, vma->vm_start, vma->vm_end);
unmap_page_range(&tlb, vma, vma->vm_start, vma->vm_end,
NULL);
tlb_finish_mmu(&tlb, vma->vm_start, vma->vm_end);
}
}
pr_info("oom_reaper: reaped process %d (%s), now anon-rss:%lukB, file-rss:%lukB, shmem-rss:%lukB\n",
task_pid_nr(tsk), tsk->comm,
K(get_mm_counter(mm, MM_ANONPAGES)),
K(get_mm_counter(mm, MM_FILEPAGES)),
K(get_mm_counter(mm, MM_SHMEMPAGES)));
up_read(&mm->mmap_sem);
trace_finish_task_reaping(tsk->pid);
unlock_oom:
mutex_unlock(&oom_lock);
return ret;
}
#define MAX_OOM_REAP_RETRIES 10
static void oom_reap_task(struct task_struct *tsk)
{
int attempts = 0;
struct mm_struct *mm = tsk->signal->oom_mm;
/* Retry the down_read_trylock(mmap_sem) a few times */
while (attempts++ < MAX_OOM_REAP_RETRIES && !__oom_reap_task_mm(tsk, mm))
schedule_timeout_idle(HZ/10);
if (attempts <= MAX_OOM_REAP_RETRIES)
goto done;
pr_info("oom_reaper: unable to reap pid:%d (%s)\n",
task_pid_nr(tsk), tsk->comm);
debug_show_all_locks();
done:
tsk->oom_reaper_list = NULL;
/*
* Hide this mm from OOM killer because it has been either reaped or
* somebody can't call up_write(mmap_sem).
*/
set_bit(MMF_OOM_SKIP, &mm->flags);
/* Drop a reference taken by wake_oom_reaper */
put_task_struct(tsk);
}
static int oom_reaper(void *unused)
{
while (true) {
struct task_struct *tsk = NULL;
wait_event_freezable(oom_reaper_wait, oom_reaper_list != NULL);
spin_lock(&oom_reaper_lock);
if (oom_reaper_list != NULL) {
tsk = oom_reaper_list;
oom_reaper_list = tsk->oom_reaper_list;
}
spin_unlock(&oom_reaper_lock);
if (tsk)
oom_reap_task(tsk);
}
return 0;
}
static void wake_oom_reaper(struct task_struct *tsk)
{
/* tsk is already queued? */
if (tsk == oom_reaper_list || tsk->oom_reaper_list)
return;
get_task_struct(tsk);
spin_lock(&oom_reaper_lock);
tsk->oom_reaper_list = oom_reaper_list;
oom_reaper_list = tsk;
spin_unlock(&oom_reaper_lock);
trace_wake_reaper(tsk->pid);
wake_up(&oom_reaper_wait);
}
static int __init oom_init(void)
{
oom_reaper_th = kthread_run(oom_reaper, NULL, "oom_reaper");
return 0;
}
subsys_initcall(oom_init)
#else
static inline void wake_oom_reaper(struct task_struct *tsk)
{
}
#endif /* CONFIG_MMU */
/**
* mark_oom_victim - mark the given task as OOM victim
* @tsk: task to mark
*
* Has to be called with oom_lock held and never after
* oom has been disabled already.
*
* tsk->mm has to be non NULL and caller has to guarantee it is stable (either
* under task_lock or operate on the current).
*/
static void mark_oom_victim(struct task_struct *tsk)
{
struct mm_struct *mm = tsk->mm;
WARN_ON(oom_killer_disabled);
/* OOM killer might race with memcg OOM */
if (test_and_set_tsk_thread_flag(tsk, TIF_MEMDIE))
return;
/* oom_mm is bound to the signal struct life time. */
if (!cmpxchg(&tsk->signal->oom_mm, NULL, mm))
mmgrab(tsk->signal->oom_mm);
/*
* Make sure that the task is woken up from uninterruptible sleep
* if it is frozen because OOM killer wouldn't be able to free
* any memory and livelock. freezing_slow_path will tell the freezer
* that TIF_MEMDIE tasks should be ignored.
*/
__thaw_task(tsk);
atomic_inc(&oom_victims);
trace_mark_victim(tsk->pid);
}
/**
* exit_oom_victim - note the exit of an OOM victim
*/
void exit_oom_victim(void)
{
clear_thread_flag(TIF_MEMDIE);
if (!atomic_dec_return(&oom_victims))
wake_up_all(&oom_victims_wait);
}
/**
* oom_killer_enable - enable OOM killer
*/
void oom_killer_enable(void)
{
oom_killer_disabled = false;
pr_info("OOM killer enabled.\n");
}
/**
* oom_killer_disable - disable OOM killer
* @timeout: maximum timeout to wait for oom victims in jiffies
*
* Forces all page allocations to fail rather than trigger OOM killer.
* Will block and wait until all OOM victims are killed or the given
* timeout expires.
*
* The function cannot be called when there are runnable user tasks because
* the userspace would see unexpected allocation failures as a result. Any
* new usage of this function should be consulted with MM people.
*
* Returns true if successful and false if the OOM killer cannot be
* disabled.
*/
bool oom_killer_disable(signed long timeout)
{
signed long ret;
/*
* Make sure to not race with an ongoing OOM killer. Check that the
* current is not killed (possibly due to sharing the victim's memory).
*/
if (mutex_lock_killable(&oom_lock))
return false;
oom_killer_disabled = true;
mutex_unlock(&oom_lock);
ret = wait_event_interruptible_timeout(oom_victims_wait,
!atomic_read(&oom_victims), timeout);
if (ret <= 0) {
oom_killer_enable();
return false;
}
pr_info("OOM killer disabled.\n");
return true;
}
static inline bool __task_will_free_mem(struct task_struct *task)
{
struct signal_struct *sig = task->signal;
/*
* A coredumping process may sleep for an extended period in exit_mm(),
* so the oom killer cannot assume that the process will promptly exit
* and release memory.
*/
if (sig->flags & SIGNAL_GROUP_COREDUMP)
return false;
if (sig->flags & SIGNAL_GROUP_EXIT)
return true;
if (thread_group_empty(task) && (task->flags & PF_EXITING))
return true;
return false;
}
/*
* Checks whether the given task is dying or exiting and likely to
* release its address space. This means that all threads and processes
* sharing the same mm have to be killed or exiting.
* Caller has to make sure that task->mm is stable (hold task_lock or
* it operates on the current).
*/
static bool task_will_free_mem(struct task_struct *task)
{
struct mm_struct *mm = task->mm;
struct task_struct *p;
bool ret = true;
/*
* Skip tasks without mm because it might have passed its exit_mm and
* exit_oom_victim. oom_reaper could have rescued that but do not rely
* on that for now. We can consider find_lock_task_mm in future.
*/
if (!mm)
return false;
if (!__task_will_free_mem(task))
return false;
/*
* This task has already been drained by the oom reaper so there are
* only small chances it will free some more
*/
if (test_bit(MMF_OOM_SKIP, &mm->flags))
return false;
if (atomic_read(&mm->mm_users) <= 1)
return true;
/*
* Make sure that all tasks which share the mm with the given tasks
* are dying as well to make sure that a) nobody pins its mm and
* b) the task is also reapable by the oom reaper.
*/
rcu_read_lock();
for_each_process(p) {
if (!process_shares_mm(p, mm))
continue;
if (same_thread_group(task, p))
continue;
ret = __task_will_free_mem(p);
if (!ret)
break;
}
rcu_read_unlock();
return ret;
}
static void oom_kill_process(struct oom_control *oc, const char *message)
{
struct task_struct *p = oc->chosen;
unsigned int points = oc->chosen_points;
struct task_struct *victim = p;
struct task_struct *child;
struct task_struct *t;
struct mm_struct *mm;
unsigned int victim_points = 0;
static DEFINE_RATELIMIT_STATE(oom_rs, DEFAULT_RATELIMIT_INTERVAL,
DEFAULT_RATELIMIT_BURST);
bool can_oom_reap = true;
/*
* If the task is already exiting, don't alarm the sysadmin or kill
* its children or threads, just give it access to memory reserves
* so it can die quickly
*/
task_lock(p);
if (task_will_free_mem(p)) {
mark_oom_victim(p);
wake_oom_reaper(p);
task_unlock(p);
put_task_struct(p);
return;
}
task_unlock(p);
if (__ratelimit(&oom_rs))
dump_header(oc, p);
pr_err("%s: Kill process %d (%s) score %u or sacrifice child\n",
message, task_pid_nr(p), p->comm, points);
/*
* If any of p's children has a different mm and is eligible for kill,
* the one with the highest oom_badness() score is sacrificed for its
* parent. This attempts to lose the minimal amount of work done while
* still freeing memory.
*/
read_lock(&tasklist_lock);
for_each_thread(p, t) {
list_for_each_entry(child, &t->children, sibling) {
unsigned int child_points;
if (process_shares_mm(child, p->mm))
continue;
/*
* oom_badness() returns 0 if the thread is unkillable
*/
child_points = oom_badness(child,
oc->memcg, oc->nodemask, oc->totalpages);
if (child_points > victim_points) {
put_task_struct(victim);
victim = child;
victim_points = child_points;
get_task_struct(victim);
}
}
}
read_unlock(&tasklist_lock);
p = find_lock_task_mm(victim);
if (!p) {
put_task_struct(victim);
return;
} else if (victim != p) {
get_task_struct(p);
put_task_struct(victim);
victim = p;
}
/* Get a reference to safely compare mm after task_unlock(victim) */
mm = victim->mm;
mmgrab(mm);
/* Raise event before sending signal: task reaper must see this */
count_vm_event(OOM_KILL);
count_memcg_event_mm(mm, OOM_KILL);
/*
* We should send SIGKILL before granting access to memory reserves
* in order to prevent the OOM victim from depleting the memory
* reserves from the user space under its control.
*/
do_send_sig_info(SIGKILL, SEND_SIG_FORCED, victim, true);
mark_oom_victim(victim);
pr_err("Killed process %d (%s) total-vm:%lukB, anon-rss:%lukB, file-rss:%lukB, shmem-rss:%lukB\n",
task_pid_nr(victim), victim->comm, K(victim->mm->total_vm),
K(get_mm_counter(victim->mm, MM_ANONPAGES)),
K(get_mm_counter(victim->mm, MM_FILEPAGES)),
K(get_mm_counter(victim->mm, MM_SHMEMPAGES)));
task_unlock(victim);
/*
* Kill all user processes sharing victim->mm in other thread groups, if
* any. They don't get access to memory reserves, though, to avoid
* depletion of all memory. This prevents mm->mmap_sem livelock when an
* oom killed thread cannot exit because it requires the semaphore and
* its contended by another thread trying to allocate memory itself.
* That thread will now get access to memory reserves since it has a
* pending fatal signal.
*/
rcu_read_lock();
for_each_process(p) {
if (!process_shares_mm(p, mm))
continue;
if (same_thread_group(p, victim))
continue;
if (is_global_init(p)) {
can_oom_reap = false;
set_bit(MMF_OOM_SKIP, &mm->flags);
pr_info("oom killer %d (%s) has mm pinned by %d (%s)\n",
task_pid_nr(victim), victim->comm,
task_pid_nr(p), p->comm);
continue;
}
/*
* No use_mm() user needs to read from the userspace so we are
* ok to reap it.
*/
if (unlikely(p->flags & PF_KTHREAD))
continue;
do_send_sig_info(SIGKILL, SEND_SIG_FORCED, p, true);
}
rcu_read_unlock();
if (can_oom_reap)
wake_oom_reaper(victim);
mmdrop(mm);
put_task_struct(victim);
}
#undef K
/*
* Determines whether the kernel must panic because of the panic_on_oom sysctl.
*/
static void check_panic_on_oom(struct oom_control *oc,
enum oom_constraint constraint)
{
if (likely(!sysctl_panic_on_oom))
return;
if (sysctl_panic_on_oom != 2) {
/*
* panic_on_oom == 1 only affects CONSTRAINT_NONE, the kernel
* does not panic for cpuset, mempolicy, or memcg allocation
* failures.
*/
if (constraint != CONSTRAINT_NONE)
return;
}
/* Do not panic for oom kills triggered by sysrq */
if (is_sysrq_oom(oc))
return;
dump_header(oc, NULL);
panic("Out of memory: %s panic_on_oom is enabled\n",
sysctl_panic_on_oom == 2 ? "compulsory" : "system-wide");
}
static BLOCKING_NOTIFIER_HEAD(oom_notify_list);
int register_oom_notifier(struct notifier_block *nb)
{
return blocking_notifier_chain_register(&oom_notify_list, nb);
}
EXPORT_SYMBOL_GPL(register_oom_notifier);
int unregister_oom_notifier(struct notifier_block *nb)
{
return blocking_notifier_chain_unregister(&oom_notify_list, nb);
}
EXPORT_SYMBOL_GPL(unregister_oom_notifier);
/**
* out_of_memory - kill the "best" process when we run out of memory
* @oc: pointer to struct oom_control
*
* If we run out of memory, we have the choice between either
* killing a random task (bad), letting the system crash (worse)
* OR try to be smart about which process to kill. Note that we
* don't have to be perfect here, we just have to be good.
*/
bool out_of_memory(struct oom_control *oc)
{
unsigned long freed = 0;
enum oom_constraint constraint = CONSTRAINT_NONE;
if (oom_killer_disabled)
return false;
if (!is_memcg_oom(oc)) {
blocking_notifier_call_chain(&oom_notify_list, 0, &freed);
if (freed > 0)
/* Got some memory back in the last second. */
return true;
}
/*
* If current has a pending SIGKILL or is exiting, then automatically
* select it. The goal is to allow it to allocate so that it may
* quickly exit and free its memory.
*/
if (task_will_free_mem(current)) {
mark_oom_victim(current);
wake_oom_reaper(current);
return true;
}
/*
* The OOM killer does not compensate for IO-less reclaim.
* pagefault_out_of_memory lost its gfp context so we have to
* make sure exclude 0 mask - all other users should have at least
* ___GFP_DIRECT_RECLAIM to get here.
*/
if (oc->gfp_mask && !(oc->gfp_mask & __GFP_FS))
return true;
/*
* Check if there were limitations on the allocation (only relevant for
* NUMA and memcg) that may require different handling.
*/
constraint = constrained_alloc(oc);
if (constraint != CONSTRAINT_MEMORY_POLICY)
oc->nodemask = NULL;
check_panic_on_oom(oc, constraint);
if (!is_memcg_oom(oc) && sysctl_oom_kill_allocating_task &&
current->mm && !oom_unkillable_task(current, NULL, oc->nodemask) &&
current->signal->oom_score_adj != OOM_SCORE_ADJ_MIN) {
get_task_struct(current);
oc->chosen = current;
oom_kill_process(oc, "Out of memory (oom_kill_allocating_task)");
return true;
}
select_bad_process(oc);
/* Found nothing?!?! Either we hang forever, or we panic. */
if (!oc->chosen && !is_sysrq_oom(oc) && !is_memcg_oom(oc)) {
dump_header(oc, NULL);
panic("Out of memory and no killable processes...\n");
}
if (oc->chosen && oc->chosen != (void *)-1UL) {
oom_kill_process(oc, !is_memcg_oom(oc) ? "Out of memory" :
"Memory cgroup out of memory");
/*
* Give the killed process a good chance to exit before trying
* to allocate memory again.
*/
schedule_timeout_killable(1);
}
return !!oc->chosen;
}
/*
* The pagefault handler calls here because it is out of memory, so kill a
* memory-hogging task. If oom_lock is held by somebody else, a parallel oom
* killing is already in progress so do nothing.
*/
void pagefault_out_of_memory(void)
{
struct oom_control oc = {
.zonelist = NULL,
.nodemask = NULL,
.memcg = NULL,
.gfp_mask = 0,
.order = 0,
};
if (mem_cgroup_oom_synchronize(true))
return;
if (!mutex_trylock(&oom_lock))
return;
out_of_memory(&oc);
mutex_unlock(&oom_lock);
}