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TOMOYO Linux Cross Reference
Linux/mm/oom_kill.c

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

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