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1// SPDX-License-Identifier: GPL-2.0-only
2/*
3 * linux/mm/oom_kill.c
4 *
5 * Copyright (C) 1998,2000 Rik van Riel
6 * Thanks go out to Claus Fischer for some serious inspiration and
7 * for goading me into coding this file...
8 * Copyright (C) 2010 Google, Inc.
9 * Rewritten by David Rientjes
10 *
11 * The routines in this file are used to kill a process when
12 * we're seriously out of memory. This gets called from __alloc_pages()
13 * in mm/page_alloc.c when we really run out of memory.
14 *
15 * Since we won't call these routines often (on a well-configured
16 * machine) this file will double as a 'coding guide' and a signpost
17 * for newbie kernel hackers. It features several pointers to major
18 * kernel subsystems and hints as to where to find out what things do.
19 */
20
21#include <linux/oom.h>
22#include <linux/mm.h>
23#include <linux/err.h>
24#include <linux/gfp.h>
25#include <linux/sched.h>
26#include <linux/sched/mm.h>
27#include <linux/sched/coredump.h>
28#include <linux/sched/task.h>
29#include <linux/sched/debug.h>
30#include <linux/swap.h>
31#include <linux/syscalls.h>
32#include <linux/timex.h>
33#include <linux/jiffies.h>
34#include <linux/cpuset.h>
35#include <linux/export.h>
36#include <linux/notifier.h>
37#include <linux/memcontrol.h>
38#include <linux/mempolicy.h>
39#include <linux/security.h>
40#include <linux/ptrace.h>
41#include <linux/freezer.h>
42#include <linux/ftrace.h>
43#include <linux/ratelimit.h>
44#include <linux/kthread.h>
45#include <linux/init.h>
46#include <linux/mmu_notifier.h>
47
48#include <asm/tlb.h>
49#include "internal.h"
50#include "slab.h"
51
52#define CREATE_TRACE_POINTS
53#include <trace/events/oom.h>
54
55static int sysctl_panic_on_oom;
56static int sysctl_oom_kill_allocating_task;
57static int sysctl_oom_dump_tasks = 1;
58
59/*
60 * Serializes oom killer invocations (out_of_memory()) from all contexts to
61 * prevent from over eager oom killing (e.g. when the oom killer is invoked
62 * from different domains).
63 *
64 * oom_killer_disable() relies on this lock to stabilize oom_killer_disabled
65 * and mark_oom_victim
66 */
67DEFINE_MUTEX(oom_lock);
68/* Serializes oom_score_adj and oom_score_adj_min updates */
69DEFINE_MUTEX(oom_adj_mutex);
70
71static inline bool is_memcg_oom(struct oom_control *oc)
72{
73 return oc->memcg != NULL;
74}
75
76#ifdef CONFIG_NUMA
77/**
78 * oom_cpuset_eligible() - check task eligibility for kill
79 * @start: task struct of which task to consider
80 * @oc: pointer to struct oom_control
81 *
82 * Task eligibility is determined by whether or not a candidate task, @tsk,
83 * shares the same mempolicy nodes as current if it is bound by such a policy
84 * and whether or not it has the same set of allowed cpuset nodes.
85 *
86 * This function is assuming oom-killer context and 'current' has triggered
87 * the oom-killer.
88 */
89static bool oom_cpuset_eligible(struct task_struct *start,
90 struct oom_control *oc)
91{
92 struct task_struct *tsk;
93 bool ret = false;
94 const nodemask_t *mask = oc->nodemask;
95
96 rcu_read_lock();
97 for_each_thread(start, tsk) {
98 if (mask) {
99 /*
100 * If this is a mempolicy constrained oom, tsk's
101 * cpuset is irrelevant. Only return true if its
102 * mempolicy intersects current, otherwise it may be
103 * needlessly killed.
104 */
105 ret = mempolicy_in_oom_domain(tsk, mask);
106 } else {
107 /*
108 * This is not a mempolicy constrained oom, so only
109 * check the mems of tsk's cpuset.
110 */
111 ret = cpuset_mems_allowed_intersects(current, tsk);
112 }
113 if (ret)
114 break;
115 }
116 rcu_read_unlock();
117
118 return ret;
119}
120#else
121static bool oom_cpuset_eligible(struct task_struct *tsk, struct oom_control *oc)
122{
123 return true;
124}
125#endif /* CONFIG_NUMA */
126
127/*
128 * The process p may have detached its own ->mm while exiting or through
129 * kthread_use_mm(), but one or more of its subthreads may still have a valid
130 * pointer. Return p, or any of its subthreads with a valid ->mm, with
131 * task_lock() held.
132 */
133struct task_struct *find_lock_task_mm(struct task_struct *p)
134{
135 struct task_struct *t;
136
137 rcu_read_lock();
138
139 for_each_thread(p, t) {
140 task_lock(t);
141 if (likely(t->mm))
142 goto found;
143 task_unlock(t);
144 }
145 t = NULL;
146found:
147 rcu_read_unlock();
148
149 return t;
150}
151
152/*
153 * order == -1 means the oom kill is required by sysrq, otherwise only
154 * for display purposes.
155 */
156static inline bool is_sysrq_oom(struct oom_control *oc)
157{
158 return oc->order == -1;
159}
160
161/* return true if the task is not adequate as candidate victim task. */
162static bool oom_unkillable_task(struct task_struct *p)
163{
164 if (is_global_init(p))
165 return true;
166 if (p->flags & PF_KTHREAD)
167 return true;
168 return false;
169}
170
171/*
172 * Check whether unreclaimable slab amount is greater than
173 * all user memory(LRU pages).
174 * dump_unreclaimable_slab() could help in the case that
175 * oom due to too much unreclaimable slab used by kernel.
176*/
177static bool should_dump_unreclaim_slab(void)
178{
179 unsigned long nr_lru;
180
181 nr_lru = global_node_page_state(NR_ACTIVE_ANON) +
182 global_node_page_state(NR_INACTIVE_ANON) +
183 global_node_page_state(NR_ACTIVE_FILE) +
184 global_node_page_state(NR_INACTIVE_FILE) +
185 global_node_page_state(NR_ISOLATED_ANON) +
186 global_node_page_state(NR_ISOLATED_FILE) +
187 global_node_page_state(NR_UNEVICTABLE);
188
189 return (global_node_page_state_pages(NR_SLAB_UNRECLAIMABLE_B) > nr_lru);
190}
191
192/**
193 * oom_badness - heuristic function to determine which candidate task to kill
194 * @p: task struct of which task we should calculate
195 * @totalpages: total present RAM allowed for page allocation
196 *
197 * The heuristic for determining which task to kill is made to be as simple and
198 * predictable as possible. The goal is to return the highest value for the
199 * task consuming the most memory to avoid subsequent oom failures.
200 */
201long oom_badness(struct task_struct *p, unsigned long totalpages)
202{
203 long points;
204 long adj;
205
206 if (oom_unkillable_task(p))
207 return LONG_MIN;
208
209 p = find_lock_task_mm(p);
210 if (!p)
211 return LONG_MIN;
212
213 /*
214 * Do not even consider tasks which are explicitly marked oom
215 * unkillable or have been already oom reaped or the are in
216 * the middle of vfork
217 */
218 adj = (long)p->signal->oom_score_adj;
219 if (adj == OOM_SCORE_ADJ_MIN ||
220 test_bit(MMF_OOM_SKIP, &p->mm->flags) ||
221 in_vfork(p)) {
222 task_unlock(p);
223 return LONG_MIN;
224 }
225
226 /*
227 * The baseline for the badness score is the proportion of RAM that each
228 * task's rss, pagetable and swap space use.
229 */
230 points = get_mm_rss(p->mm) + get_mm_counter(p->mm, MM_SWAPENTS) +
231 mm_pgtables_bytes(p->mm) / PAGE_SIZE;
232 task_unlock(p);
233
234 /* Normalize to oom_score_adj units */
235 adj *= totalpages / 1000;
236 points += adj;
237
238 return points;
239}
240
241static const char * const oom_constraint_text[] = {
242 [CONSTRAINT_NONE] = "CONSTRAINT_NONE",
243 [CONSTRAINT_CPUSET] = "CONSTRAINT_CPUSET",
244 [CONSTRAINT_MEMORY_POLICY] = "CONSTRAINT_MEMORY_POLICY",
245 [CONSTRAINT_MEMCG] = "CONSTRAINT_MEMCG",
246};
247
248/*
249 * Determine the type of allocation constraint.
250 */
251static enum oom_constraint constrained_alloc(struct oom_control *oc)
252{
253 struct zone *zone;
254 struct zoneref *z;
255 enum zone_type highest_zoneidx = gfp_zone(oc->gfp_mask);
256 bool cpuset_limited = false;
257 int nid;
258
259 if (is_memcg_oom(oc)) {
260 oc->totalpages = mem_cgroup_get_max(oc->memcg) ?: 1;
261 return CONSTRAINT_MEMCG;
262 }
263
264 /* Default to all available memory */
265 oc->totalpages = totalram_pages() + total_swap_pages;
266
267 if (!IS_ENABLED(CONFIG_NUMA))
268 return CONSTRAINT_NONE;
269
270 if (!oc->zonelist)
271 return CONSTRAINT_NONE;
272 /*
273 * Reach here only when __GFP_NOFAIL is used. So, we should avoid
274 * to kill current.We have to random task kill in this case.
275 * Hopefully, CONSTRAINT_THISNODE...but no way to handle it, now.
276 */
277 if (oc->gfp_mask & __GFP_THISNODE)
278 return CONSTRAINT_NONE;
279
280 /*
281 * This is not a __GFP_THISNODE allocation, so a truncated nodemask in
282 * the page allocator means a mempolicy is in effect. Cpuset policy
283 * is enforced in get_page_from_freelist().
284 */
285 if (oc->nodemask &&
286 !nodes_subset(node_states[N_MEMORY], *oc->nodemask)) {
287 oc->totalpages = total_swap_pages;
288 for_each_node_mask(nid, *oc->nodemask)
289 oc->totalpages += node_present_pages(nid);
290 return CONSTRAINT_MEMORY_POLICY;
291 }
292
293 /* Check this allocation failure is caused by cpuset's wall function */
294 for_each_zone_zonelist_nodemask(zone, z, oc->zonelist,
295 highest_zoneidx, oc->nodemask)
296 if (!cpuset_zone_allowed(zone, oc->gfp_mask))
297 cpuset_limited = true;
298
299 if (cpuset_limited) {
300 oc->totalpages = total_swap_pages;
301 for_each_node_mask(nid, cpuset_current_mems_allowed)
302 oc->totalpages += node_present_pages(nid);
303 return CONSTRAINT_CPUSET;
304 }
305 return CONSTRAINT_NONE;
306}
307
308static int oom_evaluate_task(struct task_struct *task, void *arg)
309{
310 struct oom_control *oc = arg;
311 long points;
312
313 if (oom_unkillable_task(task))
314 goto next;
315
316 /* p may not have freeable memory in nodemask */
317 if (!is_memcg_oom(oc) && !oom_cpuset_eligible(task, oc))
318 goto next;
319
320 /*
321 * This task already has access to memory reserves and is being killed.
322 * Don't allow any other task to have access to the reserves unless
323 * the task has MMF_OOM_SKIP because chances that it would release
324 * any memory is quite low.
325 */
326 if (!is_sysrq_oom(oc) && tsk_is_oom_victim(task)) {
327 if (test_bit(MMF_OOM_SKIP, &task->signal->oom_mm->flags))
328 goto next;
329 goto abort;
330 }
331
332 /*
333 * If task is allocating a lot of memory and has been marked to be
334 * killed first if it triggers an oom, then select it.
335 */
336 if (oom_task_origin(task)) {
337 points = LONG_MAX;
338 goto select;
339 }
340
341 points = oom_badness(task, oc->totalpages);
342 if (points == LONG_MIN || points < oc->chosen_points)
343 goto next;
344
345select:
346 if (oc->chosen)
347 put_task_struct(oc->chosen);
348 get_task_struct(task);
349 oc->chosen = task;
350 oc->chosen_points = points;
351next:
352 return 0;
353abort:
354 if (oc->chosen)
355 put_task_struct(oc->chosen);
356 oc->chosen = (void *)-1UL;
357 return 1;
358}
359
360/*
361 * Simple selection loop. We choose the process with the highest number of
362 * 'points'. In case scan was aborted, oc->chosen is set to -1.
363 */
364static void select_bad_process(struct oom_control *oc)
365{
366 oc->chosen_points = LONG_MIN;
367
368 if (is_memcg_oom(oc))
369 mem_cgroup_scan_tasks(oc->memcg, oom_evaluate_task, oc);
370 else {
371 struct task_struct *p;
372
373 rcu_read_lock();
374 for_each_process(p)
375 if (oom_evaluate_task(p, oc))
376 break;
377 rcu_read_unlock();
378 }
379}
380
381static int dump_task(struct task_struct *p, void *arg)
382{
383 struct oom_control *oc = arg;
384 struct task_struct *task;
385
386 if (oom_unkillable_task(p))
387 return 0;
388
389 /* p may not have freeable memory in nodemask */
390 if (!is_memcg_oom(oc) && !oom_cpuset_eligible(p, oc))
391 return 0;
392
393 task = find_lock_task_mm(p);
394 if (!task) {
395 /*
396 * All of p's threads have already detached their mm's. There's
397 * no need to report them; they can't be oom killed anyway.
398 */
399 return 0;
400 }
401
402 pr_info("[%7d] %5d %5d %8lu %8lu %8ld %8lu %5hd %s\n",
403 task->pid, from_kuid(&init_user_ns, task_uid(task)),
404 task->tgid, task->mm->total_vm, get_mm_rss(task->mm),
405 mm_pgtables_bytes(task->mm),
406 get_mm_counter(task->mm, MM_SWAPENTS),
407 task->signal->oom_score_adj, task->comm);
408 task_unlock(task);
409
410 return 0;
411}
412
413/**
414 * dump_tasks - dump current memory state of all system tasks
415 * @oc: pointer to struct oom_control
416 *
417 * Dumps the current memory state of all eligible tasks. Tasks not in the same
418 * memcg, not in the same cpuset, or bound to a disjoint set of mempolicy nodes
419 * are not shown.
420 * State information includes task's pid, uid, tgid, vm size, rss,
421 * pgtables_bytes, swapents, oom_score_adj value, and name.
422 */
423static void dump_tasks(struct oom_control *oc)
424{
425 pr_info("Tasks state (memory values in pages):\n");
426 pr_info("[ pid ] uid tgid total_vm rss pgtables_bytes swapents oom_score_adj name\n");
427
428 if (is_memcg_oom(oc))
429 mem_cgroup_scan_tasks(oc->memcg, dump_task, oc);
430 else {
431 struct task_struct *p;
432
433 rcu_read_lock();
434 for_each_process(p)
435 dump_task(p, oc);
436 rcu_read_unlock();
437 }
438}
439
440static void dump_oom_summary(struct oom_control *oc, struct task_struct *victim)
441{
442 /* one line summary of the oom killer context. */
443 pr_info("oom-kill:constraint=%s,nodemask=%*pbl",
444 oom_constraint_text[oc->constraint],
445 nodemask_pr_args(oc->nodemask));
446 cpuset_print_current_mems_allowed();
447 mem_cgroup_print_oom_context(oc->memcg, victim);
448 pr_cont(",task=%s,pid=%d,uid=%d\n", victim->comm, victim->pid,
449 from_kuid(&init_user_ns, task_uid(victim)));
450}
451
452static void dump_header(struct oom_control *oc, struct task_struct *p)
453{
454 pr_warn("%s invoked oom-killer: gfp_mask=%#x(%pGg), order=%d, oom_score_adj=%hd\n",
455 current->comm, oc->gfp_mask, &oc->gfp_mask, oc->order,
456 current->signal->oom_score_adj);
457 if (!IS_ENABLED(CONFIG_COMPACTION) && oc->order)
458 pr_warn("COMPACTION is disabled!!!\n");
459
460 dump_stack();
461 if (is_memcg_oom(oc))
462 mem_cgroup_print_oom_meminfo(oc->memcg);
463 else {
464 __show_mem(SHOW_MEM_FILTER_NODES, oc->nodemask, gfp_zone(oc->gfp_mask));
465 if (should_dump_unreclaim_slab())
466 dump_unreclaimable_slab();
467 }
468 if (sysctl_oom_dump_tasks)
469 dump_tasks(oc);
470 if (p)
471 dump_oom_summary(oc, p);
472}
473
474/*
475 * Number of OOM victims in flight
476 */
477static atomic_t oom_victims = ATOMIC_INIT(0);
478static DECLARE_WAIT_QUEUE_HEAD(oom_victims_wait);
479
480static bool oom_killer_disabled __read_mostly;
481
482#define K(x) ((x) << (PAGE_SHIFT-10))
483
484/*
485 * task->mm can be NULL if the task is the exited group leader. So to
486 * determine whether the task is using a particular mm, we examine all the
487 * task's threads: if one of those is using this mm then this task was also
488 * using it.
489 */
490bool process_shares_mm(struct task_struct *p, struct mm_struct *mm)
491{
492 struct task_struct *t;
493
494 for_each_thread(p, t) {
495 struct mm_struct *t_mm = READ_ONCE(t->mm);
496 if (t_mm)
497 return t_mm == mm;
498 }
499 return false;
500}
501
502#ifdef CONFIG_MMU
503/*
504 * OOM Reaper kernel thread which tries to reap the memory used by the OOM
505 * victim (if that is possible) to help the OOM killer to move on.
506 */
507static struct task_struct *oom_reaper_th;
508static DECLARE_WAIT_QUEUE_HEAD(oom_reaper_wait);
509static struct task_struct *oom_reaper_list;
510static DEFINE_SPINLOCK(oom_reaper_lock);
511
512static bool __oom_reap_task_mm(struct mm_struct *mm)
513{
514 struct vm_area_struct *vma;
515 bool ret = true;
516 VMA_ITERATOR(vmi, mm, 0);
517
518 /*
519 * Tell all users of get_user/copy_from_user etc... that the content
520 * is no longer stable. No barriers really needed because unmapping
521 * should imply barriers already and the reader would hit a page fault
522 * if it stumbled over a reaped memory.
523 */
524 set_bit(MMF_UNSTABLE, &mm->flags);
525
526 for_each_vma(vmi, vma) {
527 if (vma->vm_flags & (VM_HUGETLB|VM_PFNMAP))
528 continue;
529
530 /*
531 * Only anonymous pages have a good chance to be dropped
532 * without additional steps which we cannot afford as we
533 * are OOM already.
534 *
535 * We do not even care about fs backed pages because all
536 * which are reclaimable have already been reclaimed and
537 * we do not want to block exit_mmap by keeping mm ref
538 * count elevated without a good reason.
539 */
540 if (vma_is_anonymous(vma) || !(vma->vm_flags & VM_SHARED)) {
541 struct mmu_notifier_range range;
542 struct mmu_gather tlb;
543
544 mmu_notifier_range_init(&range, MMU_NOTIFY_UNMAP, 0,
545 vma, mm, vma->vm_start,
546 vma->vm_end);
547 tlb_gather_mmu(&tlb, mm);
548 if (mmu_notifier_invalidate_range_start_nonblock(&range)) {
549 tlb_finish_mmu(&tlb);
550 ret = false;
551 continue;
552 }
553 unmap_page_range(&tlb, vma, range.start, range.end, NULL);
554 mmu_notifier_invalidate_range_end(&range);
555 tlb_finish_mmu(&tlb);
556 }
557 }
558
559 return ret;
560}
561
562/*
563 * Reaps the address space of the give task.
564 *
565 * Returns true on success and false if none or part of the address space
566 * has been reclaimed and the caller should retry later.
567 */
568static bool oom_reap_task_mm(struct task_struct *tsk, struct mm_struct *mm)
569{
570 bool ret = true;
571
572 if (!mmap_read_trylock(mm)) {
573 trace_skip_task_reaping(tsk->pid);
574 return false;
575 }
576
577 /*
578 * MMF_OOM_SKIP is set by exit_mmap when the OOM reaper can't
579 * work on the mm anymore. The check for MMF_OOM_SKIP must run
580 * under mmap_lock for reading because it serializes against the
581 * mmap_write_lock();mmap_write_unlock() cycle in exit_mmap().
582 */
583 if (test_bit(MMF_OOM_SKIP, &mm->flags)) {
584 trace_skip_task_reaping(tsk->pid);
585 goto out_unlock;
586 }
587
588 trace_start_task_reaping(tsk->pid);
589
590 /* failed to reap part of the address space. Try again later */
591 ret = __oom_reap_task_mm(mm);
592 if (!ret)
593 goto out_finish;
594
595 pr_info("oom_reaper: reaped process %d (%s), now anon-rss:%lukB, file-rss:%lukB, shmem-rss:%lukB\n",
596 task_pid_nr(tsk), tsk->comm,
597 K(get_mm_counter(mm, MM_ANONPAGES)),
598 K(get_mm_counter(mm, MM_FILEPAGES)),
599 K(get_mm_counter(mm, MM_SHMEMPAGES)));
600out_finish:
601 trace_finish_task_reaping(tsk->pid);
602out_unlock:
603 mmap_read_unlock(mm);
604
605 return ret;
606}
607
608#define MAX_OOM_REAP_RETRIES 10
609static void oom_reap_task(struct task_struct *tsk)
610{
611 int attempts = 0;
612 struct mm_struct *mm = tsk->signal->oom_mm;
613
614 /* Retry the mmap_read_trylock(mm) a few times */
615 while (attempts++ < MAX_OOM_REAP_RETRIES && !oom_reap_task_mm(tsk, mm))
616 schedule_timeout_idle(HZ/10);
617
618 if (attempts <= MAX_OOM_REAP_RETRIES ||
619 test_bit(MMF_OOM_SKIP, &mm->flags))
620 goto done;
621
622 pr_info("oom_reaper: unable to reap pid:%d (%s)\n",
623 task_pid_nr(tsk), tsk->comm);
624 sched_show_task(tsk);
625 debug_show_all_locks();
626
627done:
628 tsk->oom_reaper_list = NULL;
629
630 /*
631 * Hide this mm from OOM killer because it has been either reaped or
632 * somebody can't call mmap_write_unlock(mm).
633 */
634 set_bit(MMF_OOM_SKIP, &mm->flags);
635
636 /* Drop a reference taken by queue_oom_reaper */
637 put_task_struct(tsk);
638}
639
640static int oom_reaper(void *unused)
641{
642 set_freezable();
643
644 while (true) {
645 struct task_struct *tsk = NULL;
646
647 wait_event_freezable(oom_reaper_wait, oom_reaper_list != NULL);
648 spin_lock_irq(&oom_reaper_lock);
649 if (oom_reaper_list != NULL) {
650 tsk = oom_reaper_list;
651 oom_reaper_list = tsk->oom_reaper_list;
652 }
653 spin_unlock_irq(&oom_reaper_lock);
654
655 if (tsk)
656 oom_reap_task(tsk);
657 }
658
659 return 0;
660}
661
662static void wake_oom_reaper(struct timer_list *timer)
663{
664 struct task_struct *tsk = container_of(timer, struct task_struct,
665 oom_reaper_timer);
666 struct mm_struct *mm = tsk->signal->oom_mm;
667 unsigned long flags;
668
669 /* The victim managed to terminate on its own - see exit_mmap */
670 if (test_bit(MMF_OOM_SKIP, &mm->flags)) {
671 put_task_struct(tsk);
672 return;
673 }
674
675 spin_lock_irqsave(&oom_reaper_lock, flags);
676 tsk->oom_reaper_list = oom_reaper_list;
677 oom_reaper_list = tsk;
678 spin_unlock_irqrestore(&oom_reaper_lock, flags);
679 trace_wake_reaper(tsk->pid);
680 wake_up(&oom_reaper_wait);
681}
682
683/*
684 * Give the OOM victim time to exit naturally before invoking the oom_reaping.
685 * The timers timeout is arbitrary... the longer it is, the longer the worst
686 * case scenario for the OOM can take. If it is too small, the oom_reaper can
687 * get in the way and release resources needed by the process exit path.
688 * e.g. The futex robust list can sit in Anon|Private memory that gets reaped
689 * before the exit path is able to wake the futex waiters.
690 */
691#define OOM_REAPER_DELAY (2*HZ)
692static void queue_oom_reaper(struct task_struct *tsk)
693{
694 /* mm is already queued? */
695 if (test_and_set_bit(MMF_OOM_REAP_QUEUED, &tsk->signal->oom_mm->flags))
696 return;
697
698 get_task_struct(tsk);
699 timer_setup(&tsk->oom_reaper_timer, wake_oom_reaper, 0);
700 tsk->oom_reaper_timer.expires = jiffies + OOM_REAPER_DELAY;
701 add_timer(&tsk->oom_reaper_timer);
702}
703
704#ifdef CONFIG_SYSCTL
705static struct ctl_table vm_oom_kill_table[] = {
706 {
707 .procname = "panic_on_oom",
708 .data = &sysctl_panic_on_oom,
709 .maxlen = sizeof(sysctl_panic_on_oom),
710 .mode = 0644,
711 .proc_handler = proc_dointvec_minmax,
712 .extra1 = SYSCTL_ZERO,
713 .extra2 = SYSCTL_TWO,
714 },
715 {
716 .procname = "oom_kill_allocating_task",
717 .data = &sysctl_oom_kill_allocating_task,
718 .maxlen = sizeof(sysctl_oom_kill_allocating_task),
719 .mode = 0644,
720 .proc_handler = proc_dointvec,
721 },
722 {
723 .procname = "oom_dump_tasks",
724 .data = &sysctl_oom_dump_tasks,
725 .maxlen = sizeof(sysctl_oom_dump_tasks),
726 .mode = 0644,
727 .proc_handler = proc_dointvec,
728 },
729 {}
730};
731#endif
732
733static int __init oom_init(void)
734{
735 oom_reaper_th = kthread_run(oom_reaper, NULL, "oom_reaper");
736#ifdef CONFIG_SYSCTL
737 register_sysctl_init("vm", vm_oom_kill_table);
738#endif
739 return 0;
740}
741subsys_initcall(oom_init)
742#else
743static inline void queue_oom_reaper(struct task_struct *tsk)
744{
745}
746#endif /* CONFIG_MMU */
747
748/**
749 * mark_oom_victim - mark the given task as OOM victim
750 * @tsk: task to mark
751 *
752 * Has to be called with oom_lock held and never after
753 * oom has been disabled already.
754 *
755 * tsk->mm has to be non NULL and caller has to guarantee it is stable (either
756 * under task_lock or operate on the current).
757 */
758static void mark_oom_victim(struct task_struct *tsk)
759{
760 struct mm_struct *mm = tsk->mm;
761
762 WARN_ON(oom_killer_disabled);
763 /* OOM killer might race with memcg OOM */
764 if (test_and_set_tsk_thread_flag(tsk, TIF_MEMDIE))
765 return;
766
767 /* oom_mm is bound to the signal struct life time. */
768 if (!cmpxchg(&tsk->signal->oom_mm, NULL, mm))
769 mmgrab(tsk->signal->oom_mm);
770
771 /*
772 * Make sure that the task is woken up from uninterruptible sleep
773 * if it is frozen because OOM killer wouldn't be able to free
774 * any memory and livelock. freezing_slow_path will tell the freezer
775 * that TIF_MEMDIE tasks should be ignored.
776 */
777 __thaw_task(tsk);
778 atomic_inc(&oom_victims);
779 trace_mark_victim(tsk->pid);
780}
781
782/**
783 * exit_oom_victim - note the exit of an OOM victim
784 */
785void exit_oom_victim(void)
786{
787 clear_thread_flag(TIF_MEMDIE);
788
789 if (!atomic_dec_return(&oom_victims))
790 wake_up_all(&oom_victims_wait);
791}
792
793/**
794 * oom_killer_enable - enable OOM killer
795 */
796void oom_killer_enable(void)
797{
798 oom_killer_disabled = false;
799 pr_info("OOM killer enabled.\n");
800}
801
802/**
803 * oom_killer_disable - disable OOM killer
804 * @timeout: maximum timeout to wait for oom victims in jiffies
805 *
806 * Forces all page allocations to fail rather than trigger OOM killer.
807 * Will block and wait until all OOM victims are killed or the given
808 * timeout expires.
809 *
810 * The function cannot be called when there are runnable user tasks because
811 * the userspace would see unexpected allocation failures as a result. Any
812 * new usage of this function should be consulted with MM people.
813 *
814 * Returns true if successful and false if the OOM killer cannot be
815 * disabled.
816 */
817bool oom_killer_disable(signed long timeout)
818{
819 signed long ret;
820
821 /*
822 * Make sure to not race with an ongoing OOM killer. Check that the
823 * current is not killed (possibly due to sharing the victim's memory).
824 */
825 if (mutex_lock_killable(&oom_lock))
826 return false;
827 oom_killer_disabled = true;
828 mutex_unlock(&oom_lock);
829
830 ret = wait_event_interruptible_timeout(oom_victims_wait,
831 !atomic_read(&oom_victims), timeout);
832 if (ret <= 0) {
833 oom_killer_enable();
834 return false;
835 }
836 pr_info("OOM killer disabled.\n");
837
838 return true;
839}
840
841static inline bool __task_will_free_mem(struct task_struct *task)
842{
843 struct signal_struct *sig = task->signal;
844
845 /*
846 * A coredumping process may sleep for an extended period in
847 * coredump_task_exit(), so the oom killer cannot assume that
848 * the process will promptly exit and release memory.
849 */
850 if (sig->core_state)
851 return false;
852
853 if (sig->flags & SIGNAL_GROUP_EXIT)
854 return true;
855
856 if (thread_group_empty(task) && (task->flags & PF_EXITING))
857 return true;
858
859 return false;
860}
861
862/*
863 * Checks whether the given task is dying or exiting and likely to
864 * release its address space. This means that all threads and processes
865 * sharing the same mm have to be killed or exiting.
866 * Caller has to make sure that task->mm is stable (hold task_lock or
867 * it operates on the current).
868 */
869static bool task_will_free_mem(struct task_struct *task)
870{
871 struct mm_struct *mm = task->mm;
872 struct task_struct *p;
873 bool ret = true;
874
875 /*
876 * Skip tasks without mm because it might have passed its exit_mm and
877 * exit_oom_victim. oom_reaper could have rescued that but do not rely
878 * on that for now. We can consider find_lock_task_mm in future.
879 */
880 if (!mm)
881 return false;
882
883 if (!__task_will_free_mem(task))
884 return false;
885
886 /*
887 * This task has already been drained by the oom reaper so there are
888 * only small chances it will free some more
889 */
890 if (test_bit(MMF_OOM_SKIP, &mm->flags))
891 return false;
892
893 if (atomic_read(&mm->mm_users) <= 1)
894 return true;
895
896 /*
897 * Make sure that all tasks which share the mm with the given tasks
898 * are dying as well to make sure that a) nobody pins its mm and
899 * b) the task is also reapable by the oom reaper.
900 */
901 rcu_read_lock();
902 for_each_process(p) {
903 if (!process_shares_mm(p, mm))
904 continue;
905 if (same_thread_group(task, p))
906 continue;
907 ret = __task_will_free_mem(p);
908 if (!ret)
909 break;
910 }
911 rcu_read_unlock();
912
913 return ret;
914}
915
916static void __oom_kill_process(struct task_struct *victim, const char *message)
917{
918 struct task_struct *p;
919 struct mm_struct *mm;
920 bool can_oom_reap = true;
921
922 p = find_lock_task_mm(victim);
923 if (!p) {
924 pr_info("%s: OOM victim %d (%s) is already exiting. Skip killing the task\n",
925 message, task_pid_nr(victim), victim->comm);
926 put_task_struct(victim);
927 return;
928 } else if (victim != p) {
929 get_task_struct(p);
930 put_task_struct(victim);
931 victim = p;
932 }
933
934 /* Get a reference to safely compare mm after task_unlock(victim) */
935 mm = victim->mm;
936 mmgrab(mm);
937
938 /* Raise event before sending signal: task reaper must see this */
939 count_vm_event(OOM_KILL);
940 memcg_memory_event_mm(mm, MEMCG_OOM_KILL);
941
942 /*
943 * We should send SIGKILL before granting access to memory reserves
944 * in order to prevent the OOM victim from depleting the memory
945 * reserves from the user space under its control.
946 */
947 do_send_sig_info(SIGKILL, SEND_SIG_PRIV, victim, PIDTYPE_TGID);
948 mark_oom_victim(victim);
949 pr_err("%s: Killed process %d (%s) total-vm:%lukB, anon-rss:%lukB, file-rss:%lukB, shmem-rss:%lukB, UID:%u pgtables:%lukB oom_score_adj:%hd\n",
950 message, task_pid_nr(victim), victim->comm, K(mm->total_vm),
951 K(get_mm_counter(mm, MM_ANONPAGES)),
952 K(get_mm_counter(mm, MM_FILEPAGES)),
953 K(get_mm_counter(mm, MM_SHMEMPAGES)),
954 from_kuid(&init_user_ns, task_uid(victim)),
955 mm_pgtables_bytes(mm) >> 10, victim->signal->oom_score_adj);
956 task_unlock(victim);
957
958 /*
959 * Kill all user processes sharing victim->mm in other thread groups, if
960 * any. They don't get access to memory reserves, though, to avoid
961 * depletion of all memory. This prevents mm->mmap_lock livelock when an
962 * oom killed thread cannot exit because it requires the semaphore and
963 * its contended by another thread trying to allocate memory itself.
964 * That thread will now get access to memory reserves since it has a
965 * pending fatal signal.
966 */
967 rcu_read_lock();
968 for_each_process(p) {
969 if (!process_shares_mm(p, mm))
970 continue;
971 if (same_thread_group(p, victim))
972 continue;
973 if (is_global_init(p)) {
974 can_oom_reap = false;
975 set_bit(MMF_OOM_SKIP, &mm->flags);
976 pr_info("oom killer %d (%s) has mm pinned by %d (%s)\n",
977 task_pid_nr(victim), victim->comm,
978 task_pid_nr(p), p->comm);
979 continue;
980 }
981 /*
982 * No kthread_use_mm() user needs to read from the userspace so
983 * we are ok to reap it.
984 */
985 if (unlikely(p->flags & PF_KTHREAD))
986 continue;
987 do_send_sig_info(SIGKILL, SEND_SIG_PRIV, p, PIDTYPE_TGID);
988 }
989 rcu_read_unlock();
990
991 if (can_oom_reap)
992 queue_oom_reaper(victim);
993
994 mmdrop(mm);
995 put_task_struct(victim);
996}
997#undef K
998
999/*
1000 * Kill provided task unless it's secured by setting
1001 * oom_score_adj to OOM_SCORE_ADJ_MIN.
1002 */
1003static int oom_kill_memcg_member(struct task_struct *task, void *message)
1004{
1005 if (task->signal->oom_score_adj != OOM_SCORE_ADJ_MIN &&
1006 !is_global_init(task)) {
1007 get_task_struct(task);
1008 __oom_kill_process(task, message);
1009 }
1010 return 0;
1011}
1012
1013static void oom_kill_process(struct oom_control *oc, const char *message)
1014{
1015 struct task_struct *victim = oc->chosen;
1016 struct mem_cgroup *oom_group;
1017 static DEFINE_RATELIMIT_STATE(oom_rs, DEFAULT_RATELIMIT_INTERVAL,
1018 DEFAULT_RATELIMIT_BURST);
1019
1020 /*
1021 * If the task is already exiting, don't alarm the sysadmin or kill
1022 * its children or threads, just give it access to memory reserves
1023 * so it can die quickly
1024 */
1025 task_lock(victim);
1026 if (task_will_free_mem(victim)) {
1027 mark_oom_victim(victim);
1028 queue_oom_reaper(victim);
1029 task_unlock(victim);
1030 put_task_struct(victim);
1031 return;
1032 }
1033 task_unlock(victim);
1034
1035 if (__ratelimit(&oom_rs))
1036 dump_header(oc, victim);
1037
1038 /*
1039 * Do we need to kill the entire memory cgroup?
1040 * Or even one of the ancestor memory cgroups?
1041 * Check this out before killing the victim task.
1042 */
1043 oom_group = mem_cgroup_get_oom_group(victim, oc->memcg);
1044
1045 __oom_kill_process(victim, message);
1046
1047 /*
1048 * If necessary, kill all tasks in the selected memory cgroup.
1049 */
1050 if (oom_group) {
1051 memcg_memory_event(oom_group, MEMCG_OOM_GROUP_KILL);
1052 mem_cgroup_print_oom_group(oom_group);
1053 mem_cgroup_scan_tasks(oom_group, oom_kill_memcg_member,
1054 (void *)message);
1055 mem_cgroup_put(oom_group);
1056 }
1057}
1058
1059/*
1060 * Determines whether the kernel must panic because of the panic_on_oom sysctl.
1061 */
1062static void check_panic_on_oom(struct oom_control *oc)
1063{
1064 if (likely(!sysctl_panic_on_oom))
1065 return;
1066 if (sysctl_panic_on_oom != 2) {
1067 /*
1068 * panic_on_oom == 1 only affects CONSTRAINT_NONE, the kernel
1069 * does not panic for cpuset, mempolicy, or memcg allocation
1070 * failures.
1071 */
1072 if (oc->constraint != CONSTRAINT_NONE)
1073 return;
1074 }
1075 /* Do not panic for oom kills triggered by sysrq */
1076 if (is_sysrq_oom(oc))
1077 return;
1078 dump_header(oc, NULL);
1079 panic("Out of memory: %s panic_on_oom is enabled\n",
1080 sysctl_panic_on_oom == 2 ? "compulsory" : "system-wide");
1081}
1082
1083static BLOCKING_NOTIFIER_HEAD(oom_notify_list);
1084
1085int register_oom_notifier(struct notifier_block *nb)
1086{
1087 return blocking_notifier_chain_register(&oom_notify_list, nb);
1088}
1089EXPORT_SYMBOL_GPL(register_oom_notifier);
1090
1091int unregister_oom_notifier(struct notifier_block *nb)
1092{
1093 return blocking_notifier_chain_unregister(&oom_notify_list, nb);
1094}
1095EXPORT_SYMBOL_GPL(unregister_oom_notifier);
1096
1097/**
1098 * out_of_memory - kill the "best" process when we run out of memory
1099 * @oc: pointer to struct oom_control
1100 *
1101 * If we run out of memory, we have the choice between either
1102 * killing a random task (bad), letting the system crash (worse)
1103 * OR try to be smart about which process to kill. Note that we
1104 * don't have to be perfect here, we just have to be good.
1105 */
1106bool out_of_memory(struct oom_control *oc)
1107{
1108 unsigned long freed = 0;
1109
1110 if (oom_killer_disabled)
1111 return false;
1112
1113 if (!is_memcg_oom(oc)) {
1114 blocking_notifier_call_chain(&oom_notify_list, 0, &freed);
1115 if (freed > 0 && !is_sysrq_oom(oc))
1116 /* Got some memory back in the last second. */
1117 return true;
1118 }
1119
1120 /*
1121 * If current has a pending SIGKILL or is exiting, then automatically
1122 * select it. The goal is to allow it to allocate so that it may
1123 * quickly exit and free its memory.
1124 */
1125 if (task_will_free_mem(current)) {
1126 mark_oom_victim(current);
1127 queue_oom_reaper(current);
1128 return true;
1129 }
1130
1131 /*
1132 * The OOM killer does not compensate for IO-less reclaim.
1133 * pagefault_out_of_memory lost its gfp context so we have to
1134 * make sure exclude 0 mask - all other users should have at least
1135 * ___GFP_DIRECT_RECLAIM to get here. But mem_cgroup_oom() has to
1136 * invoke the OOM killer even if it is a GFP_NOFS allocation.
1137 */
1138 if (oc->gfp_mask && !(oc->gfp_mask & __GFP_FS) && !is_memcg_oom(oc))
1139 return true;
1140
1141 /*
1142 * Check if there were limitations on the allocation (only relevant for
1143 * NUMA and memcg) that may require different handling.
1144 */
1145 oc->constraint = constrained_alloc(oc);
1146 if (oc->constraint != CONSTRAINT_MEMORY_POLICY)
1147 oc->nodemask = NULL;
1148 check_panic_on_oom(oc);
1149
1150 if (!is_memcg_oom(oc) && sysctl_oom_kill_allocating_task &&
1151 current->mm && !oom_unkillable_task(current) &&
1152 oom_cpuset_eligible(current, oc) &&
1153 current->signal->oom_score_adj != OOM_SCORE_ADJ_MIN) {
1154 get_task_struct(current);
1155 oc->chosen = current;
1156 oom_kill_process(oc, "Out of memory (oom_kill_allocating_task)");
1157 return true;
1158 }
1159
1160 select_bad_process(oc);
1161 /* Found nothing?!?! */
1162 if (!oc->chosen) {
1163 dump_header(oc, NULL);
1164 pr_warn("Out of memory and no killable processes...\n");
1165 /*
1166 * If we got here due to an actual allocation at the
1167 * system level, we cannot survive this and will enter
1168 * an endless loop in the allocator. Bail out now.
1169 */
1170 if (!is_sysrq_oom(oc) && !is_memcg_oom(oc))
1171 panic("System is deadlocked on memory\n");
1172 }
1173 if (oc->chosen && oc->chosen != (void *)-1UL)
1174 oom_kill_process(oc, !is_memcg_oom(oc) ? "Out of memory" :
1175 "Memory cgroup out of memory");
1176 return !!oc->chosen;
1177}
1178
1179/*
1180 * The pagefault handler calls here because some allocation has failed. We have
1181 * to take care of the memcg OOM here because this is the only safe context without
1182 * any locks held but let the oom killer triggered from the allocation context care
1183 * about the global OOM.
1184 */
1185void pagefault_out_of_memory(void)
1186{
1187 static DEFINE_RATELIMIT_STATE(pfoom_rs, DEFAULT_RATELIMIT_INTERVAL,
1188 DEFAULT_RATELIMIT_BURST);
1189
1190 if (mem_cgroup_oom_synchronize(true))
1191 return;
1192
1193 if (fatal_signal_pending(current))
1194 return;
1195
1196 if (__ratelimit(&pfoom_rs))
1197 pr_warn("Huh VM_FAULT_OOM leaked out to the #PF handler. Retrying PF\n");
1198}
1199
1200SYSCALL_DEFINE2(process_mrelease, int, pidfd, unsigned int, flags)
1201{
1202#ifdef CONFIG_MMU
1203 struct mm_struct *mm = NULL;
1204 struct task_struct *task;
1205 struct task_struct *p;
1206 unsigned int f_flags;
1207 bool reap = false;
1208 long ret = 0;
1209
1210 if (flags)
1211 return -EINVAL;
1212
1213 task = pidfd_get_task(pidfd, &f_flags);
1214 if (IS_ERR(task))
1215 return PTR_ERR(task);
1216
1217 /*
1218 * Make sure to choose a thread which still has a reference to mm
1219 * during the group exit
1220 */
1221 p = find_lock_task_mm(task);
1222 if (!p) {
1223 ret = -ESRCH;
1224 goto put_task;
1225 }
1226
1227 mm = p->mm;
1228 mmgrab(mm);
1229
1230 if (task_will_free_mem(p))
1231 reap = true;
1232 else {
1233 /* Error only if the work has not been done already */
1234 if (!test_bit(MMF_OOM_SKIP, &mm->flags))
1235 ret = -EINVAL;
1236 }
1237 task_unlock(p);
1238
1239 if (!reap)
1240 goto drop_mm;
1241
1242 if (mmap_read_lock_killable(mm)) {
1243 ret = -EINTR;
1244 goto drop_mm;
1245 }
1246 /*
1247 * Check MMF_OOM_SKIP again under mmap_read_lock protection to ensure
1248 * possible change in exit_mmap is seen
1249 */
1250 if (!test_bit(MMF_OOM_SKIP, &mm->flags) && !__oom_reap_task_mm(mm))
1251 ret = -EAGAIN;
1252 mmap_read_unlock(mm);
1253
1254drop_mm:
1255 mmdrop(mm);
1256put_task:
1257 put_task_struct(task);
1258 return ret;
1259#else
1260 return -ENOSYS;
1261#endif /* CONFIG_MMU */
1262}
1/*
2 * linux/mm/oom_kill.c
3 *
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
9 *
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.
13 *
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.
18 */
19
20#include <linux/oom.h>
21#include <linux/mm.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>
40
41#include <asm/tlb.h>
42#include "internal.h"
43
44#define CREATE_TRACE_POINTS
45#include <trace/events/oom.h>
46
47int sysctl_panic_on_oom;
48int sysctl_oom_kill_allocating_task;
49int sysctl_oom_dump_tasks = 1;
50
51DEFINE_MUTEX(oom_lock);
52
53#ifdef CONFIG_NUMA
54/**
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
58 *
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.
62 */
63static bool has_intersects_mems_allowed(struct task_struct *start,
64 const nodemask_t *mask)
65{
66 struct task_struct *tsk;
67 bool ret = false;
68
69 rcu_read_lock();
70 for_each_thread(start, tsk) {
71 if (mask) {
72 /*
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
76 * needlessly killed.
77 */
78 ret = mempolicy_nodemask_intersects(tsk, mask);
79 } else {
80 /*
81 * This is not a mempolicy constrained oom, so only
82 * check the mems of tsk's cpuset.
83 */
84 ret = cpuset_mems_allowed_intersects(current, tsk);
85 }
86 if (ret)
87 break;
88 }
89 rcu_read_unlock();
90
91 return ret;
92}
93#else
94static bool has_intersects_mems_allowed(struct task_struct *tsk,
95 const nodemask_t *mask)
96{
97 return true;
98}
99#endif /* CONFIG_NUMA */
100
101/*
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
105 * task_lock() held.
106 */
107struct task_struct *find_lock_task_mm(struct task_struct *p)
108{
109 struct task_struct *t;
110
111 rcu_read_lock();
112
113 for_each_thread(p, t) {
114 task_lock(t);
115 if (likely(t->mm))
116 goto found;
117 task_unlock(t);
118 }
119 t = NULL;
120found:
121 rcu_read_unlock();
122
123 return t;
124}
125
126/*
127 * order == -1 means the oom kill is required by sysrq, otherwise only
128 * for display purposes.
129 */
130static inline bool is_sysrq_oom(struct oom_control *oc)
131{
132 return oc->order == -1;
133}
134
135static inline bool is_memcg_oom(struct oom_control *oc)
136{
137 return oc->memcg != NULL;
138}
139
140/* return true if the task is not adequate as candidate victim task. */
141static bool oom_unkillable_task(struct task_struct *p,
142 struct mem_cgroup *memcg, const nodemask_t *nodemask)
143{
144 if (is_global_init(p))
145 return true;
146 if (p->flags & PF_KTHREAD)
147 return true;
148
149 /* When mem_cgroup_out_of_memory() and p is not member of the group */
150 if (memcg && !task_in_mem_cgroup(p, memcg))
151 return true;
152
153 /* p may not have freeable memory in nodemask */
154 if (!has_intersects_mems_allowed(p, nodemask))
155 return true;
156
157 return false;
158}
159
160/**
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
164 *
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.
168 */
169unsigned long oom_badness(struct task_struct *p, struct mem_cgroup *memcg,
170 const nodemask_t *nodemask, unsigned long totalpages)
171{
172 long points;
173 long adj;
174
175 if (oom_unkillable_task(p, memcg, nodemask))
176 return 0;
177
178 p = find_lock_task_mm(p);
179 if (!p)
180 return 0;
181
182 /*
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
186 */
187 adj = (long)p->signal->oom_score_adj;
188 if (adj == OOM_SCORE_ADJ_MIN ||
189 test_bit(MMF_OOM_SKIP, &p->mm->flags) ||
190 in_vfork(p)) {
191 task_unlock(p);
192 return 0;
193 }
194
195 /*
196 * The baseline for the badness score is the proportion of RAM that each
197 * task's rss, pagetable and swap space use.
198 */
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);
201 task_unlock(p);
202
203 /*
204 * Root processes get 3% bonus, just like the __vm_enough_memory()
205 * implementation used by LSMs.
206 */
207 if (has_capability_noaudit(p, CAP_SYS_ADMIN))
208 points -= (points * 3) / 100;
209
210 /* Normalize to oom_score_adj units */
211 adj *= totalpages / 1000;
212 points += adj;
213
214 /*
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).
217 */
218 return points > 0 ? points : 1;
219}
220
221enum oom_constraint {
222 CONSTRAINT_NONE,
223 CONSTRAINT_CPUSET,
224 CONSTRAINT_MEMORY_POLICY,
225 CONSTRAINT_MEMCG,
226};
227
228/*
229 * Determine the type of allocation constraint.
230 */
231static enum oom_constraint constrained_alloc(struct oom_control *oc)
232{
233 struct zone *zone;
234 struct zoneref *z;
235 enum zone_type high_zoneidx = gfp_zone(oc->gfp_mask);
236 bool cpuset_limited = false;
237 int nid;
238
239 if (is_memcg_oom(oc)) {
240 oc->totalpages = mem_cgroup_get_limit(oc->memcg) ?: 1;
241 return CONSTRAINT_MEMCG;
242 }
243
244 /* Default to all available memory */
245 oc->totalpages = totalram_pages + total_swap_pages;
246
247 if (!IS_ENABLED(CONFIG_NUMA))
248 return CONSTRAINT_NONE;
249
250 if (!oc->zonelist)
251 return CONSTRAINT_NONE;
252 /*
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.
256 */
257 if (oc->gfp_mask & __GFP_THISNODE)
258 return CONSTRAINT_NONE;
259
260 /*
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().
264 */
265 if (oc->nodemask &&
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;
271 }
272
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;
278
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;
284 }
285 return CONSTRAINT_NONE;
286}
287
288static int oom_evaluate_task(struct task_struct *task, void *arg)
289{
290 struct oom_control *oc = arg;
291 unsigned long points;
292
293 if (oom_unkillable_task(task, NULL, oc->nodemask))
294 goto next;
295
296 /*
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_SKIP because chances that it would release
300 * any memory is quite low.
301 */
302 if (!is_sysrq_oom(oc) && tsk_is_oom_victim(task)) {
303 if (test_bit(MMF_OOM_SKIP, &task->signal->oom_mm->flags))
304 goto next;
305 goto abort;
306 }
307
308 /*
309 * If task is allocating a lot of memory and has been marked to be
310 * killed first if it triggers an oom, then select it.
311 */
312 if (oom_task_origin(task)) {
313 points = ULONG_MAX;
314 goto select;
315 }
316
317 points = oom_badness(task, NULL, oc->nodemask, oc->totalpages);
318 if (!points || points < oc->chosen_points)
319 goto next;
320
321 /* Prefer thread group leaders for display purposes */
322 if (points == oc->chosen_points && thread_group_leader(oc->chosen))
323 goto next;
324select:
325 if (oc->chosen)
326 put_task_struct(oc->chosen);
327 get_task_struct(task);
328 oc->chosen = task;
329 oc->chosen_points = points;
330next:
331 return 0;
332abort:
333 if (oc->chosen)
334 put_task_struct(oc->chosen);
335 oc->chosen = (void *)-1UL;
336 return 1;
337}
338
339/*
340 * Simple selection loop. We choose the process with the highest number of
341 * 'points'. In case scan was aborted, oc->chosen is set to -1.
342 */
343static void select_bad_process(struct oom_control *oc)
344{
345 if (is_memcg_oom(oc))
346 mem_cgroup_scan_tasks(oc->memcg, oom_evaluate_task, oc);
347 else {
348 struct task_struct *p;
349
350 rcu_read_lock();
351 for_each_process(p)
352 if (oom_evaluate_task(p, oc))
353 break;
354 rcu_read_unlock();
355 }
356
357 oc->chosen_points = oc->chosen_points * 1000 / oc->totalpages;
358}
359
360/**
361 * dump_tasks - dump current memory state of all system tasks
362 * @memcg: current's memory controller, if constrained
363 * @nodemask: nodemask passed to page allocator for mempolicy ooms
364 *
365 * Dumps the current memory state of all eligible tasks. Tasks not in the same
366 * memcg, not in the same cpuset, or bound to a disjoint set of mempolicy nodes
367 * are not shown.
368 * State information includes task's pid, uid, tgid, vm size, rss, nr_ptes,
369 * swapents, oom_score_adj value, and name.
370 */
371static void dump_tasks(struct mem_cgroup *memcg, const nodemask_t *nodemask)
372{
373 struct task_struct *p;
374 struct task_struct *task;
375
376 pr_info("[ pid ] uid tgid total_vm rss nr_ptes nr_pmds swapents oom_score_adj name\n");
377 rcu_read_lock();
378 for_each_process(p) {
379 if (oom_unkillable_task(p, memcg, nodemask))
380 continue;
381
382 task = find_lock_task_mm(p);
383 if (!task) {
384 /*
385 * This is a kthread or all of p's threads have already
386 * detached their mm's. There's no need to report
387 * them; they can't be oom killed anyway.
388 */
389 continue;
390 }
391
392 pr_info("[%5d] %5d %5d %8lu %8lu %7ld %7ld %8lu %5hd %s\n",
393 task->pid, from_kuid(&init_user_ns, task_uid(task)),
394 task->tgid, task->mm->total_vm, get_mm_rss(task->mm),
395 atomic_long_read(&task->mm->nr_ptes),
396 mm_nr_pmds(task->mm),
397 get_mm_counter(task->mm, MM_SWAPENTS),
398 task->signal->oom_score_adj, task->comm);
399 task_unlock(task);
400 }
401 rcu_read_unlock();
402}
403
404static void dump_header(struct oom_control *oc, struct task_struct *p)
405{
406 nodemask_t *nm = (oc->nodemask) ? oc->nodemask : &cpuset_current_mems_allowed;
407
408 pr_warn("%s invoked oom-killer: gfp_mask=%#x(%pGg), nodemask=%*pbl, order=%d, oom_score_adj=%hd\n",
409 current->comm, oc->gfp_mask, &oc->gfp_mask,
410 nodemask_pr_args(nm), oc->order,
411 current->signal->oom_score_adj);
412 if (!IS_ENABLED(CONFIG_COMPACTION) && oc->order)
413 pr_warn("COMPACTION is disabled!!!\n");
414
415 cpuset_print_current_mems_allowed();
416 dump_stack();
417 if (oc->memcg)
418 mem_cgroup_print_oom_info(oc->memcg, p);
419 else
420 show_mem(SHOW_MEM_FILTER_NODES);
421 if (sysctl_oom_dump_tasks)
422 dump_tasks(oc->memcg, oc->nodemask);
423}
424
425/*
426 * Number of OOM victims in flight
427 */
428static atomic_t oom_victims = ATOMIC_INIT(0);
429static DECLARE_WAIT_QUEUE_HEAD(oom_victims_wait);
430
431static bool oom_killer_disabled __read_mostly;
432
433#define K(x) ((x) << (PAGE_SHIFT-10))
434
435/*
436 * task->mm can be NULL if the task is the exited group leader. So to
437 * determine whether the task is using a particular mm, we examine all the
438 * task's threads: if one of those is using this mm then this task was also
439 * using it.
440 */
441bool process_shares_mm(struct task_struct *p, struct mm_struct *mm)
442{
443 struct task_struct *t;
444
445 for_each_thread(p, t) {
446 struct mm_struct *t_mm = READ_ONCE(t->mm);
447 if (t_mm)
448 return t_mm == mm;
449 }
450 return false;
451}
452
453
454#ifdef CONFIG_MMU
455/*
456 * OOM Reaper kernel thread which tries to reap the memory used by the OOM
457 * victim (if that is possible) to help the OOM killer to move on.
458 */
459static struct task_struct *oom_reaper_th;
460static DECLARE_WAIT_QUEUE_HEAD(oom_reaper_wait);
461static struct task_struct *oom_reaper_list;
462static DEFINE_SPINLOCK(oom_reaper_lock);
463
464static bool __oom_reap_task_mm(struct task_struct *tsk, struct mm_struct *mm)
465{
466 struct mmu_gather tlb;
467 struct vm_area_struct *vma;
468 struct zap_details details = {.check_swap_entries = true,
469 .ignore_dirty = true};
470 bool ret = true;
471
472 /*
473 * We have to make sure to not race with the victim exit path
474 * and cause premature new oom victim selection:
475 * __oom_reap_task_mm exit_mm
476 * mmget_not_zero
477 * mmput
478 * atomic_dec_and_test
479 * exit_oom_victim
480 * [...]
481 * out_of_memory
482 * select_bad_process
483 * # no TIF_MEMDIE task selects new victim
484 * unmap_page_range # frees some memory
485 */
486 mutex_lock(&oom_lock);
487
488 if (!down_read_trylock(&mm->mmap_sem)) {
489 ret = false;
490 goto unlock_oom;
491 }
492
493 /*
494 * increase mm_users only after we know we will reap something so
495 * that the mmput_async is called only when we have reaped something
496 * and delayed __mmput doesn't matter that much
497 */
498 if (!mmget_not_zero(mm)) {
499 up_read(&mm->mmap_sem);
500 goto unlock_oom;
501 }
502
503 /*
504 * Tell all users of get_user/copy_from_user etc... that the content
505 * is no longer stable. No barriers really needed because unmapping
506 * should imply barriers already and the reader would hit a page fault
507 * if it stumbled over a reaped memory.
508 */
509 set_bit(MMF_UNSTABLE, &mm->flags);
510
511 tlb_gather_mmu(&tlb, mm, 0, -1);
512 for (vma = mm->mmap ; vma; vma = vma->vm_next) {
513 if (is_vm_hugetlb_page(vma))
514 continue;
515
516 /*
517 * mlocked VMAs require explicit munlocking before unmap.
518 * Let's keep it simple here and skip such VMAs.
519 */
520 if (vma->vm_flags & VM_LOCKED)
521 continue;
522
523 /*
524 * Only anonymous pages have a good chance to be dropped
525 * without additional steps which we cannot afford as we
526 * are OOM already.
527 *
528 * We do not even care about fs backed pages because all
529 * which are reclaimable have already been reclaimed and
530 * we do not want to block exit_mmap by keeping mm ref
531 * count elevated without a good reason.
532 */
533 if (vma_is_anonymous(vma) || !(vma->vm_flags & VM_SHARED))
534 unmap_page_range(&tlb, vma, vma->vm_start, vma->vm_end,
535 &details);
536 }
537 tlb_finish_mmu(&tlb, 0, -1);
538 pr_info("oom_reaper: reaped process %d (%s), now anon-rss:%lukB, file-rss:%lukB, shmem-rss:%lukB\n",
539 task_pid_nr(tsk), tsk->comm,
540 K(get_mm_counter(mm, MM_ANONPAGES)),
541 K(get_mm_counter(mm, MM_FILEPAGES)),
542 K(get_mm_counter(mm, MM_SHMEMPAGES)));
543 up_read(&mm->mmap_sem);
544
545 /*
546 * Drop our reference but make sure the mmput slow path is called from a
547 * different context because we shouldn't risk we get stuck there and
548 * put the oom_reaper out of the way.
549 */
550 mmput_async(mm);
551unlock_oom:
552 mutex_unlock(&oom_lock);
553 return ret;
554}
555
556#define MAX_OOM_REAP_RETRIES 10
557static void oom_reap_task(struct task_struct *tsk)
558{
559 int attempts = 0;
560 struct mm_struct *mm = tsk->signal->oom_mm;
561
562 /* Retry the down_read_trylock(mmap_sem) a few times */
563 while (attempts++ < MAX_OOM_REAP_RETRIES && !__oom_reap_task_mm(tsk, mm))
564 schedule_timeout_idle(HZ/10);
565
566 if (attempts <= MAX_OOM_REAP_RETRIES)
567 goto done;
568
569
570 pr_info("oom_reaper: unable to reap pid:%d (%s)\n",
571 task_pid_nr(tsk), tsk->comm);
572 debug_show_all_locks();
573
574done:
575 tsk->oom_reaper_list = NULL;
576
577 /*
578 * Hide this mm from OOM killer because it has been either reaped or
579 * somebody can't call up_write(mmap_sem).
580 */
581 set_bit(MMF_OOM_SKIP, &mm->flags);
582
583 /* Drop a reference taken by wake_oom_reaper */
584 put_task_struct(tsk);
585}
586
587static int oom_reaper(void *unused)
588{
589 while (true) {
590 struct task_struct *tsk = NULL;
591
592 wait_event_freezable(oom_reaper_wait, oom_reaper_list != NULL);
593 spin_lock(&oom_reaper_lock);
594 if (oom_reaper_list != NULL) {
595 tsk = oom_reaper_list;
596 oom_reaper_list = tsk->oom_reaper_list;
597 }
598 spin_unlock(&oom_reaper_lock);
599
600 if (tsk)
601 oom_reap_task(tsk);
602 }
603
604 return 0;
605}
606
607static void wake_oom_reaper(struct task_struct *tsk)
608{
609 if (!oom_reaper_th)
610 return;
611
612 /* tsk is already queued? */
613 if (tsk == oom_reaper_list || tsk->oom_reaper_list)
614 return;
615
616 get_task_struct(tsk);
617
618 spin_lock(&oom_reaper_lock);
619 tsk->oom_reaper_list = oom_reaper_list;
620 oom_reaper_list = tsk;
621 spin_unlock(&oom_reaper_lock);
622 wake_up(&oom_reaper_wait);
623}
624
625static int __init oom_init(void)
626{
627 oom_reaper_th = kthread_run(oom_reaper, NULL, "oom_reaper");
628 if (IS_ERR(oom_reaper_th)) {
629 pr_err("Unable to start OOM reaper %ld. Continuing regardless\n",
630 PTR_ERR(oom_reaper_th));
631 oom_reaper_th = NULL;
632 }
633 return 0;
634}
635subsys_initcall(oom_init)
636#else
637static inline void wake_oom_reaper(struct task_struct *tsk)
638{
639}
640#endif /* CONFIG_MMU */
641
642/**
643 * mark_oom_victim - mark the given task as OOM victim
644 * @tsk: task to mark
645 *
646 * Has to be called with oom_lock held and never after
647 * oom has been disabled already.
648 *
649 * tsk->mm has to be non NULL and caller has to guarantee it is stable (either
650 * under task_lock or operate on the current).
651 */
652static void mark_oom_victim(struct task_struct *tsk)
653{
654 struct mm_struct *mm = tsk->mm;
655
656 WARN_ON(oom_killer_disabled);
657 /* OOM killer might race with memcg OOM */
658 if (test_and_set_tsk_thread_flag(tsk, TIF_MEMDIE))
659 return;
660
661 /* oom_mm is bound to the signal struct life time. */
662 if (!cmpxchg(&tsk->signal->oom_mm, NULL, mm))
663 atomic_inc(&tsk->signal->oom_mm->mm_count);
664
665 /*
666 * Make sure that the task is woken up from uninterruptible sleep
667 * if it is frozen because OOM killer wouldn't be able to free
668 * any memory and livelock. freezing_slow_path will tell the freezer
669 * that TIF_MEMDIE tasks should be ignored.
670 */
671 __thaw_task(tsk);
672 atomic_inc(&oom_victims);
673}
674
675/**
676 * exit_oom_victim - note the exit of an OOM victim
677 */
678void exit_oom_victim(void)
679{
680 clear_thread_flag(TIF_MEMDIE);
681
682 if (!atomic_dec_return(&oom_victims))
683 wake_up_all(&oom_victims_wait);
684}
685
686/**
687 * oom_killer_enable - enable OOM killer
688 */
689void oom_killer_enable(void)
690{
691 oom_killer_disabled = false;
692}
693
694/**
695 * oom_killer_disable - disable OOM killer
696 * @timeout: maximum timeout to wait for oom victims in jiffies
697 *
698 * Forces all page allocations to fail rather than trigger OOM killer.
699 * Will block and wait until all OOM victims are killed or the given
700 * timeout expires.
701 *
702 * The function cannot be called when there are runnable user tasks because
703 * the userspace would see unexpected allocation failures as a result. Any
704 * new usage of this function should be consulted with MM people.
705 *
706 * Returns true if successful and false if the OOM killer cannot be
707 * disabled.
708 */
709bool oom_killer_disable(signed long timeout)
710{
711 signed long ret;
712
713 /*
714 * Make sure to not race with an ongoing OOM killer. Check that the
715 * current is not killed (possibly due to sharing the victim's memory).
716 */
717 if (mutex_lock_killable(&oom_lock))
718 return false;
719 oom_killer_disabled = true;
720 mutex_unlock(&oom_lock);
721
722 ret = wait_event_interruptible_timeout(oom_victims_wait,
723 !atomic_read(&oom_victims), timeout);
724 if (ret <= 0) {
725 oom_killer_enable();
726 return false;
727 }
728
729 return true;
730}
731
732static inline bool __task_will_free_mem(struct task_struct *task)
733{
734 struct signal_struct *sig = task->signal;
735
736 /*
737 * A coredumping process may sleep for an extended period in exit_mm(),
738 * so the oom killer cannot assume that the process will promptly exit
739 * and release memory.
740 */
741 if (sig->flags & SIGNAL_GROUP_COREDUMP)
742 return false;
743
744 if (sig->flags & SIGNAL_GROUP_EXIT)
745 return true;
746
747 if (thread_group_empty(task) && (task->flags & PF_EXITING))
748 return true;
749
750 return false;
751}
752
753/*
754 * Checks whether the given task is dying or exiting and likely to
755 * release its address space. This means that all threads and processes
756 * sharing the same mm have to be killed or exiting.
757 * Caller has to make sure that task->mm is stable (hold task_lock or
758 * it operates on the current).
759 */
760static bool task_will_free_mem(struct task_struct *task)
761{
762 struct mm_struct *mm = task->mm;
763 struct task_struct *p;
764 bool ret = true;
765
766 /*
767 * Skip tasks without mm because it might have passed its exit_mm and
768 * exit_oom_victim. oom_reaper could have rescued that but do not rely
769 * on that for now. We can consider find_lock_task_mm in future.
770 */
771 if (!mm)
772 return false;
773
774 if (!__task_will_free_mem(task))
775 return false;
776
777 /*
778 * This task has already been drained by the oom reaper so there are
779 * only small chances it will free some more
780 */
781 if (test_bit(MMF_OOM_SKIP, &mm->flags))
782 return false;
783
784 if (atomic_read(&mm->mm_users) <= 1)
785 return true;
786
787 /*
788 * Make sure that all tasks which share the mm with the given tasks
789 * are dying as well to make sure that a) nobody pins its mm and
790 * b) the task is also reapable by the oom reaper.
791 */
792 rcu_read_lock();
793 for_each_process(p) {
794 if (!process_shares_mm(p, mm))
795 continue;
796 if (same_thread_group(task, p))
797 continue;
798 ret = __task_will_free_mem(p);
799 if (!ret)
800 break;
801 }
802 rcu_read_unlock();
803
804 return ret;
805}
806
807static void oom_kill_process(struct oom_control *oc, const char *message)
808{
809 struct task_struct *p = oc->chosen;
810 unsigned int points = oc->chosen_points;
811 struct task_struct *victim = p;
812 struct task_struct *child;
813 struct task_struct *t;
814 struct mm_struct *mm;
815 unsigned int victim_points = 0;
816 static DEFINE_RATELIMIT_STATE(oom_rs, DEFAULT_RATELIMIT_INTERVAL,
817 DEFAULT_RATELIMIT_BURST);
818 bool can_oom_reap = true;
819
820 /*
821 * If the task is already exiting, don't alarm the sysadmin or kill
822 * its children or threads, just set TIF_MEMDIE so it can die quickly
823 */
824 task_lock(p);
825 if (task_will_free_mem(p)) {
826 mark_oom_victim(p);
827 wake_oom_reaper(p);
828 task_unlock(p);
829 put_task_struct(p);
830 return;
831 }
832 task_unlock(p);
833
834 if (__ratelimit(&oom_rs))
835 dump_header(oc, p);
836
837 pr_err("%s: Kill process %d (%s) score %u or sacrifice child\n",
838 message, task_pid_nr(p), p->comm, points);
839
840 /*
841 * If any of p's children has a different mm and is eligible for kill,
842 * the one with the highest oom_badness() score is sacrificed for its
843 * parent. This attempts to lose the minimal amount of work done while
844 * still freeing memory.
845 */
846 read_lock(&tasklist_lock);
847 for_each_thread(p, t) {
848 list_for_each_entry(child, &t->children, sibling) {
849 unsigned int child_points;
850
851 if (process_shares_mm(child, p->mm))
852 continue;
853 /*
854 * oom_badness() returns 0 if the thread is unkillable
855 */
856 child_points = oom_badness(child,
857 oc->memcg, oc->nodemask, oc->totalpages);
858 if (child_points > victim_points) {
859 put_task_struct(victim);
860 victim = child;
861 victim_points = child_points;
862 get_task_struct(victim);
863 }
864 }
865 }
866 read_unlock(&tasklist_lock);
867
868 p = find_lock_task_mm(victim);
869 if (!p) {
870 put_task_struct(victim);
871 return;
872 } else if (victim != p) {
873 get_task_struct(p);
874 put_task_struct(victim);
875 victim = p;
876 }
877
878 /* Get a reference to safely compare mm after task_unlock(victim) */
879 mm = victim->mm;
880 atomic_inc(&mm->mm_count);
881 /*
882 * We should send SIGKILL before setting TIF_MEMDIE in order to prevent
883 * the OOM victim from depleting the memory reserves from the user
884 * space under its control.
885 */
886 do_send_sig_info(SIGKILL, SEND_SIG_FORCED, victim, true);
887 mark_oom_victim(victim);
888 pr_err("Killed process %d (%s) total-vm:%lukB, anon-rss:%lukB, file-rss:%lukB, shmem-rss:%lukB\n",
889 task_pid_nr(victim), victim->comm, K(victim->mm->total_vm),
890 K(get_mm_counter(victim->mm, MM_ANONPAGES)),
891 K(get_mm_counter(victim->mm, MM_FILEPAGES)),
892 K(get_mm_counter(victim->mm, MM_SHMEMPAGES)));
893 task_unlock(victim);
894
895 /*
896 * Kill all user processes sharing victim->mm in other thread groups, if
897 * any. They don't get access to memory reserves, though, to avoid
898 * depletion of all memory. This prevents mm->mmap_sem livelock when an
899 * oom killed thread cannot exit because it requires the semaphore and
900 * its contended by another thread trying to allocate memory itself.
901 * That thread will now get access to memory reserves since it has a
902 * pending fatal signal.
903 */
904 rcu_read_lock();
905 for_each_process(p) {
906 if (!process_shares_mm(p, mm))
907 continue;
908 if (same_thread_group(p, victim))
909 continue;
910 if (is_global_init(p)) {
911 can_oom_reap = false;
912 set_bit(MMF_OOM_SKIP, &mm->flags);
913 pr_info("oom killer %d (%s) has mm pinned by %d (%s)\n",
914 task_pid_nr(victim), victim->comm,
915 task_pid_nr(p), p->comm);
916 continue;
917 }
918 /*
919 * No use_mm() user needs to read from the userspace so we are
920 * ok to reap it.
921 */
922 if (unlikely(p->flags & PF_KTHREAD))
923 continue;
924 do_send_sig_info(SIGKILL, SEND_SIG_FORCED, p, true);
925 }
926 rcu_read_unlock();
927
928 if (can_oom_reap)
929 wake_oom_reaper(victim);
930
931 mmdrop(mm);
932 put_task_struct(victim);
933}
934#undef K
935
936/*
937 * Determines whether the kernel must panic because of the panic_on_oom sysctl.
938 */
939static void check_panic_on_oom(struct oom_control *oc,
940 enum oom_constraint constraint)
941{
942 if (likely(!sysctl_panic_on_oom))
943 return;
944 if (sysctl_panic_on_oom != 2) {
945 /*
946 * panic_on_oom == 1 only affects CONSTRAINT_NONE, the kernel
947 * does not panic for cpuset, mempolicy, or memcg allocation
948 * failures.
949 */
950 if (constraint != CONSTRAINT_NONE)
951 return;
952 }
953 /* Do not panic for oom kills triggered by sysrq */
954 if (is_sysrq_oom(oc))
955 return;
956 dump_header(oc, NULL);
957 panic("Out of memory: %s panic_on_oom is enabled\n",
958 sysctl_panic_on_oom == 2 ? "compulsory" : "system-wide");
959}
960
961static BLOCKING_NOTIFIER_HEAD(oom_notify_list);
962
963int register_oom_notifier(struct notifier_block *nb)
964{
965 return blocking_notifier_chain_register(&oom_notify_list, nb);
966}
967EXPORT_SYMBOL_GPL(register_oom_notifier);
968
969int unregister_oom_notifier(struct notifier_block *nb)
970{
971 return blocking_notifier_chain_unregister(&oom_notify_list, nb);
972}
973EXPORT_SYMBOL_GPL(unregister_oom_notifier);
974
975/**
976 * out_of_memory - kill the "best" process when we run out of memory
977 * @oc: pointer to struct oom_control
978 *
979 * If we run out of memory, we have the choice between either
980 * killing a random task (bad), letting the system crash (worse)
981 * OR try to be smart about which process to kill. Note that we
982 * don't have to be perfect here, we just have to be good.
983 */
984bool out_of_memory(struct oom_control *oc)
985{
986 unsigned long freed = 0;
987 enum oom_constraint constraint = CONSTRAINT_NONE;
988
989 if (oom_killer_disabled)
990 return false;
991
992 if (!is_memcg_oom(oc)) {
993 blocking_notifier_call_chain(&oom_notify_list, 0, &freed);
994 if (freed > 0)
995 /* Got some memory back in the last second. */
996 return true;
997 }
998
999 /*
1000 * If current has a pending SIGKILL or is exiting, then automatically
1001 * select it. The goal is to allow it to allocate so that it may
1002 * quickly exit and free its memory.
1003 */
1004 if (task_will_free_mem(current)) {
1005 mark_oom_victim(current);
1006 wake_oom_reaper(current);
1007 return true;
1008 }
1009
1010 /*
1011 * The OOM killer does not compensate for IO-less reclaim.
1012 * pagefault_out_of_memory lost its gfp context so we have to
1013 * make sure exclude 0 mask - all other users should have at least
1014 * ___GFP_DIRECT_RECLAIM to get here.
1015 */
1016 if (oc->gfp_mask && !(oc->gfp_mask & (__GFP_FS|__GFP_NOFAIL)))
1017 return true;
1018
1019 /*
1020 * Check if there were limitations on the allocation (only relevant for
1021 * NUMA and memcg) that may require different handling.
1022 */
1023 constraint = constrained_alloc(oc);
1024 if (constraint != CONSTRAINT_MEMORY_POLICY)
1025 oc->nodemask = NULL;
1026 check_panic_on_oom(oc, constraint);
1027
1028 if (!is_memcg_oom(oc) && sysctl_oom_kill_allocating_task &&
1029 current->mm && !oom_unkillable_task(current, NULL, oc->nodemask) &&
1030 current->signal->oom_score_adj != OOM_SCORE_ADJ_MIN) {
1031 get_task_struct(current);
1032 oc->chosen = current;
1033 oom_kill_process(oc, "Out of memory (oom_kill_allocating_task)");
1034 return true;
1035 }
1036
1037 select_bad_process(oc);
1038 /* Found nothing?!?! Either we hang forever, or we panic. */
1039 if (!oc->chosen && !is_sysrq_oom(oc) && !is_memcg_oom(oc)) {
1040 dump_header(oc, NULL);
1041 panic("Out of memory and no killable processes...\n");
1042 }
1043 if (oc->chosen && oc->chosen != (void *)-1UL) {
1044 oom_kill_process(oc, !is_memcg_oom(oc) ? "Out of memory" :
1045 "Memory cgroup out of memory");
1046 /*
1047 * Give the killed process a good chance to exit before trying
1048 * to allocate memory again.
1049 */
1050 schedule_timeout_killable(1);
1051 }
1052 return !!oc->chosen;
1053}
1054
1055/*
1056 * The pagefault handler calls here because it is out of memory, so kill a
1057 * memory-hogging task. If oom_lock is held by somebody else, a parallel oom
1058 * killing is already in progress so do nothing.
1059 */
1060void pagefault_out_of_memory(void)
1061{
1062 struct oom_control oc = {
1063 .zonelist = NULL,
1064 .nodemask = NULL,
1065 .memcg = NULL,
1066 .gfp_mask = 0,
1067 .order = 0,
1068 };
1069
1070 if (mem_cgroup_oom_synchronize(true))
1071 return;
1072
1073 if (!mutex_trylock(&oom_lock))
1074 return;
1075 out_of_memory(&oc);
1076 mutex_unlock(&oom_lock);
1077}