4 * Copyright (C) 1998,2000 Rik van Riel
5 * Thanks go out to Claus Fischer for some serious inspiration and
6 * for goading me into coding this file...
7 * Copyright (C) 2010 Google, Inc.
8 * Rewritten by David Rientjes
10 * The routines in this file are used to kill a process when
11 * we're seriously out of memory. This gets called from __alloc_pages()
12 * in mm/page_alloc.c when we really run out of memory.
14 * Since we won't call these routines often (on a well-configured
15 * machine) this file will double as a 'coding guide' and a signpost
16 * for newbie kernel hackers. It features several pointers to major
17 * kernel subsystems and hints as to where to find out what things do.
20 #include <linux/oom.h>
22 #include <linux/err.h>
23 #include <linux/gfp.h>
24 #include <linux/sched.h>
25 #include <linux/swap.h>
26 #include <linux/timex.h>
27 #include <linux/jiffies.h>
28 #include <linux/cpuset.h>
29 #include <linux/export.h>
30 #include <linux/notifier.h>
31 #include <linux/memcontrol.h>
32 #include <linux/mempolicy.h>
33 #include <linux/security.h>
34 #include <linux/ptrace.h>
35 #include <linux/freezer.h>
36 #include <linux/ftrace.h>
37 #include <linux/ratelimit.h>
38 #include <linux/kthread.h>
39 #include <linux/init.h>
44 #define CREATE_TRACE_POINTS
45 #include <trace/events/oom.h>
47 int sysctl_panic_on_oom;
48 int sysctl_oom_kill_allocating_task;
49 int sysctl_oom_dump_tasks = 1;
51 DEFINE_MUTEX(oom_lock);
55 * has_intersects_mems_allowed() - check task eligiblity for kill
56 * @start: task struct of which task to consider
57 * @mask: nodemask passed to page allocator for mempolicy ooms
59 * Task eligibility is determined by whether or not a candidate task, @tsk,
60 * shares the same mempolicy nodes as current if it is bound by such a policy
61 * and whether or not it has the same set of allowed cpuset nodes.
63 static bool has_intersects_mems_allowed(struct task_struct *start,
64 const nodemask_t *mask)
66 struct task_struct *tsk;
70 for_each_thread(start, tsk) {
73 * If this is a mempolicy constrained oom, tsk's
74 * cpuset is irrelevant. Only return true if its
75 * mempolicy intersects current, otherwise it may be
78 ret = mempolicy_nodemask_intersects(tsk, mask);
81 * This is not a mempolicy constrained oom, so only
82 * check the mems of tsk's cpuset.
84 ret = cpuset_mems_allowed_intersects(current, tsk);
94 static bool has_intersects_mems_allowed(struct task_struct *tsk,
95 const nodemask_t *mask)
99 #endif /* CONFIG_NUMA */
102 * The process p may have detached its own ->mm while exiting or through
103 * use_mm(), but one or more of its subthreads may still have a valid
104 * pointer. Return p, or any of its subthreads with a valid ->mm, with
107 struct task_struct *find_lock_task_mm(struct task_struct *p)
109 struct task_struct *t;
113 for_each_thread(p, t) {
127 * order == -1 means the oom kill is required by sysrq, otherwise only
128 * for display purposes.
130 static inline bool is_sysrq_oom(struct oom_control *oc)
132 return oc->order == -1;
135 static inline bool is_memcg_oom(struct oom_control *oc)
137 return oc->memcg != NULL;
140 /* return true if the task is not adequate as candidate victim task. */
141 static bool oom_unkillable_task(struct task_struct *p,
142 struct mem_cgroup *memcg, const nodemask_t *nodemask)
144 if (is_global_init(p))
146 if (p->flags & PF_KTHREAD)
149 /* When mem_cgroup_out_of_memory() and p is not member of the group */
150 if (memcg && !task_in_mem_cgroup(p, memcg))
153 /* p may not have freeable memory in nodemask */
154 if (!has_intersects_mems_allowed(p, nodemask))
161 * oom_badness - heuristic function to determine which candidate task to kill
162 * @p: task struct of which task we should calculate
163 * @totalpages: total present RAM allowed for page allocation
165 * The heuristic for determining which task to kill is made to be as simple and
166 * predictable as possible. The goal is to return the highest value for the
167 * task consuming the most memory to avoid subsequent oom failures.
169 unsigned long oom_badness(struct task_struct *p, struct mem_cgroup *memcg,
170 const nodemask_t *nodemask, unsigned long totalpages)
175 if (oom_unkillable_task(p, memcg, nodemask))
178 p = find_lock_task_mm(p);
183 * Do not even consider tasks which are explicitly marked oom
184 * unkillable or have been already oom reaped or the are in
185 * the middle of vfork
187 adj = (long)p->signal->oom_score_adj;
188 if (adj == OOM_SCORE_ADJ_MIN ||
189 test_bit(MMF_OOM_REAPED, &p->mm->flags) ||
196 * The baseline for the badness score is the proportion of RAM that each
197 * task's rss, pagetable and swap space use.
199 points = get_mm_rss(p->mm) + get_mm_counter(p->mm, MM_SWAPENTS) +
200 atomic_long_read(&p->mm->nr_ptes) + mm_nr_pmds(p->mm);
204 * Root processes get 3% bonus, just like the __vm_enough_memory()
205 * implementation used by LSMs.
207 if (has_capability_noaudit(p, CAP_SYS_ADMIN))
208 points -= (points * 3) / 100;
210 /* Normalize to oom_score_adj units */
211 adj *= totalpages / 1000;
215 * Never return 0 for an eligible task regardless of the root bonus and
216 * oom_score_adj (oom_score_adj can't be OOM_SCORE_ADJ_MIN here).
218 return points > 0 ? points : 1;
221 enum oom_constraint {
224 CONSTRAINT_MEMORY_POLICY,
229 * Determine the type of allocation constraint.
231 static enum oom_constraint constrained_alloc(struct oom_control *oc)
235 enum zone_type high_zoneidx = gfp_zone(oc->gfp_mask);
236 bool cpuset_limited = false;
239 if (is_memcg_oom(oc)) {
240 oc->totalpages = mem_cgroup_get_limit(oc->memcg) ?: 1;
241 return CONSTRAINT_MEMCG;
244 /* Default to all available memory */
245 oc->totalpages = totalram_pages + total_swap_pages;
247 if (!IS_ENABLED(CONFIG_NUMA))
248 return CONSTRAINT_NONE;
251 return CONSTRAINT_NONE;
253 * Reach here only when __GFP_NOFAIL is used. So, we should avoid
254 * to kill current.We have to random task kill in this case.
255 * Hopefully, CONSTRAINT_THISNODE...but no way to handle it, now.
257 if (oc->gfp_mask & __GFP_THISNODE)
258 return CONSTRAINT_NONE;
261 * This is not a __GFP_THISNODE allocation, so a truncated nodemask in
262 * the page allocator means a mempolicy is in effect. Cpuset policy
263 * is enforced in get_page_from_freelist().
266 !nodes_subset(node_states[N_MEMORY], *oc->nodemask)) {
267 oc->totalpages = total_swap_pages;
268 for_each_node_mask(nid, *oc->nodemask)
269 oc->totalpages += node_spanned_pages(nid);
270 return CONSTRAINT_MEMORY_POLICY;
273 /* Check this allocation failure is caused by cpuset's wall function */
274 for_each_zone_zonelist_nodemask(zone, z, oc->zonelist,
275 high_zoneidx, oc->nodemask)
276 if (!cpuset_zone_allowed(zone, oc->gfp_mask))
277 cpuset_limited = true;
279 if (cpuset_limited) {
280 oc->totalpages = total_swap_pages;
281 for_each_node_mask(nid, cpuset_current_mems_allowed)
282 oc->totalpages += node_spanned_pages(nid);
283 return CONSTRAINT_CPUSET;
285 return CONSTRAINT_NONE;
288 static int oom_evaluate_task(struct task_struct *task, void *arg)
290 struct oom_control *oc = arg;
291 unsigned long points;
293 if (oom_unkillable_task(task, NULL, oc->nodemask))
297 * This task already has access to memory reserves and is being killed.
298 * Don't allow any other task to have access to the reserves unless
299 * the task has MMF_OOM_REAPED because chances that it would release
300 * any memory is quite low.
302 if (!is_sysrq_oom(oc) && atomic_read(&task->signal->oom_victims)) {
303 struct task_struct *p = find_lock_task_mm(task);
307 reaped = test_bit(MMF_OOM_REAPED, &p->mm->flags);
316 * If task is allocating a lot of memory and has been marked to be
317 * killed first if it triggers an oom, then select it.
319 if (oom_task_origin(task)) {
324 points = oom_badness(task, NULL, oc->nodemask, oc->totalpages);
325 if (!points || points < oc->chosen_points)
328 /* Prefer thread group leaders for display purposes */
329 if (points == oc->chosen_points && thread_group_leader(oc->chosen))
333 put_task_struct(oc->chosen);
334 get_task_struct(task);
336 oc->chosen_points = points;
341 put_task_struct(oc->chosen);
342 oc->chosen = (void *)-1UL;
347 * Simple selection loop. We choose the process with the highest number of
348 * 'points'. In case scan was aborted, oc->chosen is set to -1.
350 static void select_bad_process(struct oom_control *oc)
352 if (is_memcg_oom(oc))
353 mem_cgroup_scan_tasks(oc->memcg, oom_evaluate_task, oc);
355 struct task_struct *p;
359 if (oom_evaluate_task(p, oc))
364 oc->chosen_points = oc->chosen_points * 1000 / oc->totalpages;
368 * dump_tasks - dump current memory state of all system tasks
369 * @memcg: current's memory controller, if constrained
370 * @nodemask: nodemask passed to page allocator for mempolicy ooms
372 * Dumps the current memory state of all eligible tasks. Tasks not in the same
373 * memcg, not in the same cpuset, or bound to a disjoint set of mempolicy nodes
375 * State information includes task's pid, uid, tgid, vm size, rss, nr_ptes,
376 * swapents, oom_score_adj value, and name.
378 static void dump_tasks(struct mem_cgroup *memcg, const nodemask_t *nodemask)
380 struct task_struct *p;
381 struct task_struct *task;
383 pr_info("[ pid ] uid tgid total_vm rss nr_ptes nr_pmds swapents oom_score_adj name\n");
385 for_each_process(p) {
386 if (oom_unkillable_task(p, memcg, nodemask))
389 task = find_lock_task_mm(p);
392 * This is a kthread or all of p's threads have already
393 * detached their mm's. There's no need to report
394 * them; they can't be oom killed anyway.
399 pr_info("[%5d] %5d %5d %8lu %8lu %7ld %7ld %8lu %5hd %s\n",
400 task->pid, from_kuid(&init_user_ns, task_uid(task)),
401 task->tgid, task->mm->total_vm, get_mm_rss(task->mm),
402 atomic_long_read(&task->mm->nr_ptes),
403 mm_nr_pmds(task->mm),
404 get_mm_counter(task->mm, MM_SWAPENTS),
405 task->signal->oom_score_adj, task->comm);
411 static void dump_header(struct oom_control *oc, struct task_struct *p)
413 pr_warn("%s invoked oom-killer: gfp_mask=%#x(%pGg), order=%d, oom_score_adj=%hd\n",
414 current->comm, oc->gfp_mask, &oc->gfp_mask, oc->order,
415 current->signal->oom_score_adj);
417 cpuset_print_current_mems_allowed();
420 mem_cgroup_print_oom_info(oc->memcg, p);
422 show_mem(SHOW_MEM_FILTER_NODES);
423 if (sysctl_oom_dump_tasks)
424 dump_tasks(oc->memcg, oc->nodemask);
428 * Number of OOM victims in flight
430 static atomic_t oom_victims = ATOMIC_INIT(0);
431 static DECLARE_WAIT_QUEUE_HEAD(oom_victims_wait);
433 static bool oom_killer_disabled __read_mostly;
435 #define K(x) ((x) << (PAGE_SHIFT-10))
438 * task->mm can be NULL if the task is the exited group leader. So to
439 * determine whether the task is using a particular mm, we examine all the
440 * task's threads: if one of those is using this mm then this task was also
443 bool process_shares_mm(struct task_struct *p, struct mm_struct *mm)
445 struct task_struct *t;
447 for_each_thread(p, t) {
448 struct mm_struct *t_mm = READ_ONCE(t->mm);
458 * OOM Reaper kernel thread which tries to reap the memory used by the OOM
459 * victim (if that is possible) to help the OOM killer to move on.
461 static struct task_struct *oom_reaper_th;
462 static DECLARE_WAIT_QUEUE_HEAD(oom_reaper_wait);
463 static struct task_struct *oom_reaper_list;
464 static DEFINE_SPINLOCK(oom_reaper_lock);
466 static bool __oom_reap_task(struct task_struct *tsk)
468 struct mmu_gather tlb;
469 struct vm_area_struct *vma;
470 struct mm_struct *mm = NULL;
471 struct task_struct *p;
472 struct zap_details details = {.check_swap_entries = true,
473 .ignore_dirty = true};
477 * We have to make sure to not race with the victim exit path
478 * and cause premature new oom victim selection:
479 * __oom_reap_task exit_mm
482 * atomic_dec_and_test
487 * # no TIF_MEMDIE task selects new victim
488 * unmap_page_range # frees some memory
490 mutex_lock(&oom_lock);
493 * Make sure we find the associated mm_struct even when the particular
494 * thread has already terminated and cleared its mm.
495 * We might have race with exit path so consider our work done if there
498 p = find_lock_task_mm(tsk);
502 atomic_inc(&mm->mm_count);
505 if (!down_read_trylock(&mm->mmap_sem)) {
511 * increase mm_users only after we know we will reap something so
512 * that the mmput_async is called only when we have reaped something
513 * and delayed __mmput doesn't matter that much
515 if (!mmget_not_zero(mm)) {
516 up_read(&mm->mmap_sem);
520 tlb_gather_mmu(&tlb, mm, 0, -1);
521 for (vma = mm->mmap ; vma; vma = vma->vm_next) {
522 if (is_vm_hugetlb_page(vma))
526 * mlocked VMAs require explicit munlocking before unmap.
527 * Let's keep it simple here and skip such VMAs.
529 if (vma->vm_flags & VM_LOCKED)
533 * Only anonymous pages have a good chance to be dropped
534 * without additional steps which we cannot afford as we
537 * We do not even care about fs backed pages because all
538 * which are reclaimable have already been reclaimed and
539 * we do not want to block exit_mmap by keeping mm ref
540 * count elevated without a good reason.
542 if (vma_is_anonymous(vma) || !(vma->vm_flags & VM_SHARED))
543 unmap_page_range(&tlb, vma, vma->vm_start, vma->vm_end,
546 tlb_finish_mmu(&tlb, 0, -1);
547 pr_info("oom_reaper: reaped process %d (%s), now anon-rss:%lukB, file-rss:%lukB, shmem-rss:%lukB\n",
548 task_pid_nr(tsk), tsk->comm,
549 K(get_mm_counter(mm, MM_ANONPAGES)),
550 K(get_mm_counter(mm, MM_FILEPAGES)),
551 K(get_mm_counter(mm, MM_SHMEMPAGES)));
552 up_read(&mm->mmap_sem);
555 * This task can be safely ignored because we cannot do much more
556 * to release its memory.
558 set_bit(MMF_OOM_REAPED, &mm->flags);
560 * Drop our reference but make sure the mmput slow path is called from a
561 * different context because we shouldn't risk we get stuck there and
562 * put the oom_reaper out of the way.
568 mutex_unlock(&oom_lock);
572 #define MAX_OOM_REAP_RETRIES 10
573 static void oom_reap_task(struct task_struct *tsk)
577 /* Retry the down_read_trylock(mmap_sem) a few times */
578 while (attempts++ < MAX_OOM_REAP_RETRIES && !__oom_reap_task(tsk))
579 schedule_timeout_idle(HZ/10);
581 if (attempts > MAX_OOM_REAP_RETRIES) {
582 struct task_struct *p;
584 pr_info("oom_reaper: unable to reap pid:%d (%s)\n",
585 task_pid_nr(tsk), tsk->comm);
588 * If we've already tried to reap this task in the past and
589 * failed it probably doesn't make much sense to try yet again
590 * so hide the mm from the oom killer so that it can move on
591 * to another task with a different mm struct.
593 p = find_lock_task_mm(tsk);
595 if (test_and_set_bit(MMF_OOM_NOT_REAPABLE, &p->mm->flags)) {
596 pr_info("oom_reaper: giving up pid:%d (%s)\n",
597 task_pid_nr(tsk), tsk->comm);
598 set_bit(MMF_OOM_REAPED, &p->mm->flags);
603 debug_show_all_locks();
607 * Clear TIF_MEMDIE because the task shouldn't be sitting on a
608 * reasonably reclaimable memory anymore or it is not a good candidate
609 * for the oom victim right now because it cannot release its memory
610 * itself nor by the oom reaper.
612 tsk->oom_reaper_list = NULL;
613 exit_oom_victim(tsk);
615 /* Drop a reference taken by wake_oom_reaper */
616 put_task_struct(tsk);
619 static int oom_reaper(void *unused)
624 struct task_struct *tsk = NULL;
626 wait_event_freezable(oom_reaper_wait, oom_reaper_list != NULL);
627 spin_lock(&oom_reaper_lock);
628 if (oom_reaper_list != NULL) {
629 tsk = oom_reaper_list;
630 oom_reaper_list = tsk->oom_reaper_list;
632 spin_unlock(&oom_reaper_lock);
641 static void wake_oom_reaper(struct task_struct *tsk)
646 /* tsk is already queued? */
647 if (tsk == oom_reaper_list || tsk->oom_reaper_list)
650 get_task_struct(tsk);
652 spin_lock(&oom_reaper_lock);
653 tsk->oom_reaper_list = oom_reaper_list;
654 oom_reaper_list = tsk;
655 spin_unlock(&oom_reaper_lock);
656 wake_up(&oom_reaper_wait);
659 static int __init oom_init(void)
661 oom_reaper_th = kthread_run(oom_reaper, NULL, "oom_reaper");
662 if (IS_ERR(oom_reaper_th)) {
663 pr_err("Unable to start OOM reaper %ld. Continuing regardless\n",
664 PTR_ERR(oom_reaper_th));
665 oom_reaper_th = NULL;
669 subsys_initcall(oom_init)
671 static inline void wake_oom_reaper(struct task_struct *tsk)
674 #endif /* CONFIG_MMU */
677 * mark_oom_victim - mark the given task as OOM victim
680 * Has to be called with oom_lock held and never after
681 * oom has been disabled already.
683 static void mark_oom_victim(struct task_struct *tsk)
685 WARN_ON(oom_killer_disabled);
686 /* OOM killer might race with memcg OOM */
687 if (test_and_set_tsk_thread_flag(tsk, TIF_MEMDIE))
689 atomic_inc(&tsk->signal->oom_victims);
691 * Make sure that the task is woken up from uninterruptible sleep
692 * if it is frozen because OOM killer wouldn't be able to free
693 * any memory and livelock. freezing_slow_path will tell the freezer
694 * that TIF_MEMDIE tasks should be ignored.
697 atomic_inc(&oom_victims);
701 * exit_oom_victim - note the exit of an OOM victim
703 void exit_oom_victim(struct task_struct *tsk)
705 if (!test_and_clear_tsk_thread_flag(tsk, TIF_MEMDIE))
707 atomic_dec(&tsk->signal->oom_victims);
709 if (!atomic_dec_return(&oom_victims))
710 wake_up_all(&oom_victims_wait);
714 * oom_killer_disable - disable OOM killer
716 * Forces all page allocations to fail rather than trigger OOM killer.
717 * Will block and wait until all OOM victims are killed.
719 * The function cannot be called when there are runnable user tasks because
720 * the userspace would see unexpected allocation failures as a result. Any
721 * new usage of this function should be consulted with MM people.
723 * Returns true if successful and false if the OOM killer cannot be
726 bool oom_killer_disable(void)
729 * Make sure to not race with an ongoing OOM killer. Check that the
730 * current is not killed (possibly due to sharing the victim's memory).
732 if (mutex_lock_killable(&oom_lock))
734 oom_killer_disabled = true;
735 mutex_unlock(&oom_lock);
737 wait_event(oom_victims_wait, !atomic_read(&oom_victims));
743 * oom_killer_enable - enable OOM killer
745 void oom_killer_enable(void)
747 oom_killer_disabled = false;
750 static inline bool __task_will_free_mem(struct task_struct *task)
752 struct signal_struct *sig = task->signal;
755 * A coredumping process may sleep for an extended period in exit_mm(),
756 * so the oom killer cannot assume that the process will promptly exit
757 * and release memory.
759 if (sig->flags & SIGNAL_GROUP_COREDUMP)
762 if (sig->flags & SIGNAL_GROUP_EXIT)
765 if (thread_group_empty(task) && (task->flags & PF_EXITING))
772 * Checks whether the given task is dying or exiting and likely to
773 * release its address space. This means that all threads and processes
774 * sharing the same mm have to be killed or exiting.
775 * Caller has to make sure that task->mm is stable (hold task_lock or
776 * it operates on the current).
778 static bool task_will_free_mem(struct task_struct *task)
780 struct mm_struct *mm = task->mm;
781 struct task_struct *p;
785 * Skip tasks without mm because it might have passed its exit_mm and
786 * exit_oom_victim. oom_reaper could have rescued that but do not rely
787 * on that for now. We can consider find_lock_task_mm in future.
792 if (!__task_will_free_mem(task))
796 * This task has already been drained by the oom reaper so there are
797 * only small chances it will free some more
799 if (test_bit(MMF_OOM_REAPED, &mm->flags))
802 if (atomic_read(&mm->mm_users) <= 1)
806 * Make sure that all tasks which share the mm with the given tasks
807 * are dying as well to make sure that a) nobody pins its mm and
808 * b) the task is also reapable by the oom reaper.
811 for_each_process(p) {
812 if (!process_shares_mm(p, mm))
814 if (same_thread_group(task, p))
816 ret = __task_will_free_mem(p);
825 static void oom_kill_process(struct oom_control *oc, const char *message)
827 struct task_struct *p = oc->chosen;
828 unsigned int points = oc->chosen_points;
829 struct task_struct *victim = p;
830 struct task_struct *child;
831 struct task_struct *t;
832 struct mm_struct *mm;
833 unsigned int victim_points = 0;
834 static DEFINE_RATELIMIT_STATE(oom_rs, DEFAULT_RATELIMIT_INTERVAL,
835 DEFAULT_RATELIMIT_BURST);
836 bool can_oom_reap = true;
839 * If the task is already exiting, don't alarm the sysadmin or kill
840 * its children or threads, just set TIF_MEMDIE so it can die quickly
843 if (task_will_free_mem(p)) {
852 if (__ratelimit(&oom_rs))
855 pr_err("%s: Kill process %d (%s) score %u or sacrifice child\n",
856 message, task_pid_nr(p), p->comm, points);
859 * If any of p's children has a different mm and is eligible for kill,
860 * the one with the highest oom_badness() score is sacrificed for its
861 * parent. This attempts to lose the minimal amount of work done while
862 * still freeing memory.
864 read_lock(&tasklist_lock);
865 for_each_thread(p, t) {
866 list_for_each_entry(child, &t->children, sibling) {
867 unsigned int child_points;
869 if (process_shares_mm(child, p->mm))
872 * oom_badness() returns 0 if the thread is unkillable
874 child_points = oom_badness(child,
875 oc->memcg, oc->nodemask, oc->totalpages);
876 if (child_points > victim_points) {
877 put_task_struct(victim);
879 victim_points = child_points;
880 get_task_struct(victim);
884 read_unlock(&tasklist_lock);
886 p = find_lock_task_mm(victim);
888 put_task_struct(victim);
890 } else if (victim != p) {
892 put_task_struct(victim);
896 /* Get a reference to safely compare mm after task_unlock(victim) */
898 atomic_inc(&mm->mm_count);
900 * We should send SIGKILL before setting TIF_MEMDIE in order to prevent
901 * the OOM victim from depleting the memory reserves from the user
902 * space under its control.
904 do_send_sig_info(SIGKILL, SEND_SIG_FORCED, victim, true);
905 mark_oom_victim(victim);
906 pr_err("Killed process %d (%s) total-vm:%lukB, anon-rss:%lukB, file-rss:%lukB, shmem-rss:%lukB\n",
907 task_pid_nr(victim), victim->comm, K(victim->mm->total_vm),
908 K(get_mm_counter(victim->mm, MM_ANONPAGES)),
909 K(get_mm_counter(victim->mm, MM_FILEPAGES)),
910 K(get_mm_counter(victim->mm, MM_SHMEMPAGES)));
914 * Kill all user processes sharing victim->mm in other thread groups, if
915 * any. They don't get access to memory reserves, though, to avoid
916 * depletion of all memory. This prevents mm->mmap_sem livelock when an
917 * oom killed thread cannot exit because it requires the semaphore and
918 * its contended by another thread trying to allocate memory itself.
919 * That thread will now get access to memory reserves since it has a
920 * pending fatal signal.
923 for_each_process(p) {
924 if (!process_shares_mm(p, mm))
926 if (same_thread_group(p, victim))
928 if (unlikely(p->flags & PF_KTHREAD) || is_global_init(p)) {
930 * We cannot use oom_reaper for the mm shared by this
931 * process because it wouldn't get killed and so the
932 * memory might be still used. Hide the mm from the oom
933 * killer to guarantee OOM forward progress.
935 can_oom_reap = false;
936 set_bit(MMF_OOM_REAPED, &mm->flags);
937 pr_info("oom killer %d (%s) has mm pinned by %d (%s)\n",
938 task_pid_nr(victim), victim->comm,
939 task_pid_nr(p), p->comm);
942 do_send_sig_info(SIGKILL, SEND_SIG_FORCED, p, true);
947 wake_oom_reaper(victim);
950 put_task_struct(victim);
955 * Determines whether the kernel must panic because of the panic_on_oom sysctl.
957 static void check_panic_on_oom(struct oom_control *oc,
958 enum oom_constraint constraint)
960 if (likely(!sysctl_panic_on_oom))
962 if (sysctl_panic_on_oom != 2) {
964 * panic_on_oom == 1 only affects CONSTRAINT_NONE, the kernel
965 * does not panic for cpuset, mempolicy, or memcg allocation
968 if (constraint != CONSTRAINT_NONE)
971 /* Do not panic for oom kills triggered by sysrq */
972 if (is_sysrq_oom(oc))
974 dump_header(oc, NULL);
975 panic("Out of memory: %s panic_on_oom is enabled\n",
976 sysctl_panic_on_oom == 2 ? "compulsory" : "system-wide");
979 static BLOCKING_NOTIFIER_HEAD(oom_notify_list);
981 int register_oom_notifier(struct notifier_block *nb)
983 return blocking_notifier_chain_register(&oom_notify_list, nb);
985 EXPORT_SYMBOL_GPL(register_oom_notifier);
987 int unregister_oom_notifier(struct notifier_block *nb)
989 return blocking_notifier_chain_unregister(&oom_notify_list, nb);
991 EXPORT_SYMBOL_GPL(unregister_oom_notifier);
994 * out_of_memory - kill the "best" process when we run out of memory
995 * @oc: pointer to struct oom_control
997 * If we run out of memory, we have the choice between either
998 * killing a random task (bad), letting the system crash (worse)
999 * OR try to be smart about which process to kill. Note that we
1000 * don't have to be perfect here, we just have to be good.
1002 bool out_of_memory(struct oom_control *oc)
1004 unsigned long freed = 0;
1005 enum oom_constraint constraint = CONSTRAINT_NONE;
1007 if (oom_killer_disabled)
1010 if (!is_memcg_oom(oc)) {
1011 blocking_notifier_call_chain(&oom_notify_list, 0, &freed);
1013 /* Got some memory back in the last second. */
1018 * If current has a pending SIGKILL or is exiting, then automatically
1019 * select it. The goal is to allow it to allocate so that it may
1020 * quickly exit and free its memory.
1022 if (task_will_free_mem(current)) {
1023 mark_oom_victim(current);
1024 wake_oom_reaper(current);
1029 * The OOM killer does not compensate for IO-less reclaim.
1030 * pagefault_out_of_memory lost its gfp context so we have to
1031 * make sure exclude 0 mask - all other users should have at least
1032 * ___GFP_DIRECT_RECLAIM to get here.
1034 if (oc->gfp_mask && !(oc->gfp_mask & (__GFP_FS|__GFP_NOFAIL)))
1038 * Check if there were limitations on the allocation (only relevant for
1039 * NUMA and memcg) that may require different handling.
1041 constraint = constrained_alloc(oc);
1042 if (constraint != CONSTRAINT_MEMORY_POLICY)
1043 oc->nodemask = NULL;
1044 check_panic_on_oom(oc, constraint);
1046 if (!is_memcg_oom(oc) && sysctl_oom_kill_allocating_task &&
1047 current->mm && !oom_unkillable_task(current, NULL, oc->nodemask) &&
1048 current->signal->oom_score_adj != OOM_SCORE_ADJ_MIN) {
1049 get_task_struct(current);
1050 oc->chosen = current;
1051 oom_kill_process(oc, "Out of memory (oom_kill_allocating_task)");
1055 select_bad_process(oc);
1056 /* Found nothing?!?! Either we hang forever, or we panic. */
1057 if (!oc->chosen && !is_sysrq_oom(oc) && !is_memcg_oom(oc)) {
1058 dump_header(oc, NULL);
1059 panic("Out of memory and no killable processes...\n");
1061 if (oc->chosen && oc->chosen != (void *)-1UL) {
1062 oom_kill_process(oc, !is_memcg_oom(oc) ? "Out of memory" :
1063 "Memory cgroup out of memory");
1065 * Give the killed process a good chance to exit before trying
1066 * to allocate memory again.
1068 schedule_timeout_killable(1);
1070 return !!oc->chosen;
1074 * The pagefault handler calls here because it is out of memory, so kill a
1075 * memory-hogging task. If oom_lock is held by somebody else, a parallel oom
1076 * killing is already in progress so do nothing.
1078 void pagefault_out_of_memory(void)
1080 struct oom_control oc = {
1088 if (mem_cgroup_oom_synchronize(true))
1091 if (!mutex_trylock(&oom_lock))
1094 if (!out_of_memory(&oc)) {
1096 * There shouldn't be any user tasks runnable while the
1097 * OOM killer is disabled, so the current task has to
1098 * be a racing OOM victim for which oom_killer_disable()
1101 WARN_ON(test_thread_flag(TIF_MEMDIE));
1104 mutex_unlock(&oom_lock);