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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 /*
 57  * Serializes oom killer invocations (out_of_memory()) from all contexts to
 58  * prevent from over eager oom killing (e.g. when the oom killer is invoked
 59  * from different domains).
 60  *
 61  * oom_killer_disable() relies on this lock to stabilize oom_killer_disabled
 62  * and mark_oom_victim
 63  */
 64 DEFINE_MUTEX(oom_lock);
 65 
 66 #ifdef CONFIG_NUMA
 67 /**
 68  * has_intersects_mems_allowed() - check task eligiblity for kill
 69  * @start: task struct of which task to consider
 70  * @mask: nodemask passed to page allocator for mempolicy ooms
 71  *
 72  * Task eligibility is determined by whether or not a candidate task, @tsk,
 73  * shares the same mempolicy nodes as current if it is bound by such a policy
 74  * and whether or not it has the same set of allowed cpuset nodes.
 75  */
 76 static bool has_intersects_mems_allowed(struct task_struct *start,
 77                                         const nodemask_t *mask)
 78 {
 79         struct task_struct *tsk;
 80         bool ret = false;
 81 
 82         rcu_read_lock();
 83         for_each_thread(start, tsk) {
 84                 if (mask) {
 85                         /*
 86                          * If this is a mempolicy constrained oom, tsk's
 87                          * cpuset is irrelevant.  Only return true if its
 88                          * mempolicy intersects current, otherwise it may be
 89                          * needlessly killed.
 90                          */
 91                         ret = mempolicy_nodemask_intersects(tsk, mask);
 92                 } else {
 93                         /*
 94                          * This is not a mempolicy constrained oom, so only
 95                          * check the mems of tsk's cpuset.
 96                          */
 97                         ret = cpuset_mems_allowed_intersects(current, tsk);
 98                 }
 99                 if (ret)
100                         break;
101         }
102         rcu_read_unlock();
103 
104         return ret;
105 }
106 #else
107 static bool has_intersects_mems_allowed(struct task_struct *tsk,
108                                         const nodemask_t *mask)
109 {
110         return true;
111 }
112 #endif /* CONFIG_NUMA */
113 
114 /*
115  * The process p may have detached its own ->mm while exiting or through
116  * use_mm(), but one or more of its subthreads may still have a valid
117  * pointer.  Return p, or any of its subthreads with a valid ->mm, with
118  * task_lock() held.
119  */
120 struct task_struct *find_lock_task_mm(struct task_struct *p)
121 {
122         struct task_struct *t;
123 
124         rcu_read_lock();
125 
126         for_each_thread(p, t) {
127                 task_lock(t);
128                 if (likely(t->mm))
129                         goto found;
130                 task_unlock(t);
131         }
132         t = NULL;
133 found:
134         rcu_read_unlock();
135 
136         return t;
137 }
138 
139 /*
140  * order == -1 means the oom kill is required by sysrq, otherwise only
141  * for display purposes.
142  */
143 static inline bool is_sysrq_oom(struct oom_control *oc)
144 {
145         return oc->order == -1;
146 }
147 
148 static inline bool is_memcg_oom(struct oom_control *oc)
149 {
150         return oc->memcg != NULL;
151 }
152 
153 /* return true if the task is not adequate as candidate victim task. */
154 static bool oom_unkillable_task(struct task_struct *p,
155                 struct mem_cgroup *memcg, const nodemask_t *nodemask)
156 {
157         if (is_global_init(p))
158                 return true;
159         if (p->flags & PF_KTHREAD)
160                 return true;
161 
162         /* When mem_cgroup_out_of_memory() and p is not member of the group */
163         if (memcg && !task_in_mem_cgroup(p, memcg))
164                 return true;
165 
166         /* p may not have freeable memory in nodemask */
167         if (!has_intersects_mems_allowed(p, nodemask))
168                 return true;
169 
170         return false;
171 }
172 
173 /*
174  * Print out unreclaimble slabs info when unreclaimable slabs amount is greater
175  * than all user memory (LRU pages)
176  */
177 static bool is_dump_unreclaim_slabs(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(NR_SLAB_UNRECLAIMABLE) > 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  * @memcg: task's memory controller, if constrained
197  * @nodemask: nodemask passed to page allocator for mempolicy ooms
198  *
199  * The heuristic for determining which task to kill is made to be as simple and
200  * predictable as possible.  The goal is to return the highest value for the
201  * task consuming the most memory to avoid subsequent oom failures.
202  */
203 unsigned long oom_badness(struct task_struct *p, struct mem_cgroup *memcg,
204                           const nodemask_t *nodemask, unsigned long totalpages)
205 {
206         long points;
207         long adj;
208 
209         if (oom_unkillable_task(p, memcg, nodemask))
210                 return 0;
211 
212         p = find_lock_task_mm(p);
213         if (!p)
214                 return 0;
215 
216         /*
217          * Do not even consider tasks which are explicitly marked oom
218          * unkillable or have been already oom reaped or the are in
219          * the middle of vfork
220          */
221         adj = (long)p->signal->oom_score_adj;
222         if (adj == OOM_SCORE_ADJ_MIN ||
223                         test_bit(MMF_OOM_SKIP, &p->mm->flags) ||
224                         in_vfork(p)) {
225                 task_unlock(p);
226                 return 0;
227         }
228 
229         /*
230          * The baseline for the badness score is the proportion of RAM that each
231          * task's rss, pagetable and swap space use.
232          */
233         points = get_mm_rss(p->mm) + get_mm_counter(p->mm, MM_SWAPENTS) +
234                 mm_pgtables_bytes(p->mm) / PAGE_SIZE;
235         task_unlock(p);
236 
237         /* Normalize to oom_score_adj units */
238         adj *= totalpages / 1000;
239         points += adj;
240 
241         /*
242          * Never return 0 for an eligible task regardless of the root bonus and
243          * oom_score_adj (oom_score_adj can't be OOM_SCORE_ADJ_MIN here).
244          */
245         return points > 0 ? points : 1;
246 }
247 
248 static const char * const oom_constraint_text[] = {
249         [CONSTRAINT_NONE] = "CONSTRAINT_NONE",
250         [CONSTRAINT_CPUSET] = "CONSTRAINT_CPUSET",
251         [CONSTRAINT_MEMORY_POLICY] = "CONSTRAINT_MEMORY_POLICY",
252         [CONSTRAINT_MEMCG] = "CONSTRAINT_MEMCG",
253 };
254 
255 /*
256  * Determine the type of allocation constraint.
257  */
258 static enum oom_constraint constrained_alloc(struct oom_control *oc)
259 {
260         struct zone *zone;
261         struct zoneref *z;
262         enum zone_type high_zoneidx = gfp_zone(oc->gfp_mask);
263         bool cpuset_limited = false;
264         int nid;
265 
266         if (is_memcg_oom(oc)) {
267                 oc->totalpages = mem_cgroup_get_max(oc->memcg) ?: 1;
268                 return CONSTRAINT_MEMCG;
269         }
270 
271         /* Default to all available memory */
272         oc->totalpages = totalram_pages() + total_swap_pages;
273 
274         if (!IS_ENABLED(CONFIG_NUMA))
275                 return CONSTRAINT_NONE;
276 
277         if (!oc->zonelist)
278                 return CONSTRAINT_NONE;
279         /*
280          * Reach here only when __GFP_NOFAIL is used. So, we should avoid
281          * to kill current.We have to random task kill in this case.
282          * Hopefully, CONSTRAINT_THISNODE...but no way to handle it, now.
283          */
284         if (oc->gfp_mask & __GFP_THISNODE)
285                 return CONSTRAINT_NONE;
286 
287         /*
288          * This is not a __GFP_THISNODE allocation, so a truncated nodemask in
289          * the page allocator means a mempolicy is in effect.  Cpuset policy
290          * is enforced in get_page_from_freelist().
291          */
292         if (oc->nodemask &&
293             !nodes_subset(node_states[N_MEMORY], *oc->nodemask)) {
294                 oc->totalpages = total_swap_pages;
295                 for_each_node_mask(nid, *oc->nodemask)
296                         oc->totalpages += node_spanned_pages(nid);
297                 return CONSTRAINT_MEMORY_POLICY;
298         }
299 
300         /* Check this allocation failure is caused by cpuset's wall function */
301         for_each_zone_zonelist_nodemask(zone, z, oc->zonelist,
302                         high_zoneidx, oc->nodemask)
303                 if (!cpuset_zone_allowed(zone, oc->gfp_mask))
304                         cpuset_limited = true;
305 
306         if (cpuset_limited) {
307                 oc->totalpages = total_swap_pages;
308                 for_each_node_mask(nid, cpuset_current_mems_allowed)
309                         oc->totalpages += node_spanned_pages(nid);
310                 return CONSTRAINT_CPUSET;
311         }
312         return CONSTRAINT_NONE;
313 }
314 
315 static int oom_evaluate_task(struct task_struct *task, void *arg)
316 {
317         struct oom_control *oc = arg;
318         unsigned long points;
319 
320         if (oom_unkillable_task(task, NULL, oc->nodemask))
321                 goto next;
322 
323         /*
324          * This task already has access to memory reserves and is being killed.
325          * Don't allow any other task to have access to the reserves unless
326          * the task has MMF_OOM_SKIP because chances that it would release
327          * any memory is quite low.
328          */
329         if (!is_sysrq_oom(oc) && tsk_is_oom_victim(task)) {
330                 if (test_bit(MMF_OOM_SKIP, &task->signal->oom_mm->flags))
331                         goto next;
332                 goto abort;
333         }
334 
335         /*
336          * If task is allocating a lot of memory and has been marked to be
337          * killed first if it triggers an oom, then select it.
338          */
339         if (oom_task_origin(task)) {
340                 points = ULONG_MAX;
341                 goto select;
342         }
343 
344         points = oom_badness(task, NULL, oc->nodemask, oc->totalpages);
345         if (!points || points < oc->chosen_points)
346                 goto next;
347 
348         /* Prefer thread group leaders for display purposes */
349         if (points == oc->chosen_points && thread_group_leader(oc->chosen))
350                 goto next;
351 select:
352         if (oc->chosen)
353                 put_task_struct(oc->chosen);
354         get_task_struct(task);
355         oc->chosen = task;
356         oc->chosen_points = points;
357 next:
358         return 0;
359 abort:
360         if (oc->chosen)
361                 put_task_struct(oc->chosen);
362         oc->chosen = (void *)-1UL;
363         return 1;
364 }
365 
366 /*
367  * Simple selection loop. We choose the process with the highest number of
368  * 'points'. In case scan was aborted, oc->chosen is set to -1.
369  */
370 static void select_bad_process(struct oom_control *oc)
371 {
372         if (is_memcg_oom(oc))
373                 mem_cgroup_scan_tasks(oc->memcg, oom_evaluate_task, oc);
374         else {
375                 struct task_struct *p;
376 
377                 rcu_read_lock();
378                 for_each_process(p)
379                         if (oom_evaluate_task(p, oc))
380                                 break;
381                 rcu_read_unlock();
382         }
383 
384         oc->chosen_points = oc->chosen_points * 1000 / oc->totalpages;
385 }
386 
387 /**
388  * dump_tasks - dump current memory state of all system tasks
389  * @memcg: current's memory controller, if constrained
390  * @nodemask: nodemask passed to page allocator for mempolicy ooms
391  *
392  * Dumps the current memory state of all eligible tasks.  Tasks not in the same
393  * memcg, not in the same cpuset, or bound to a disjoint set of mempolicy nodes
394  * are not shown.
395  * State information includes task's pid, uid, tgid, vm size, rss,
396  * pgtables_bytes, swapents, oom_score_adj value, and name.
397  */
398 static void dump_tasks(struct mem_cgroup *memcg, const nodemask_t *nodemask)
399 {
400         struct task_struct *p;
401         struct task_struct *task;
402 
403         pr_info("Tasks state (memory values in pages):\n");
404         pr_info("[  pid  ]   uid  tgid total_vm      rss pgtables_bytes swapents oom_score_adj name\n");
405         rcu_read_lock();
406         for_each_process(p) {
407                 if (oom_unkillable_task(p, memcg, nodemask))
408                         continue;
409 
410                 task = find_lock_task_mm(p);
411                 if (!task) {
412                         /*
413                          * This is a kthread or all of p's threads have already
414                          * detached their mm's.  There's no need to report
415                          * them; they can't be oom killed anyway.
416                          */
417                         continue;
418                 }
419 
420                 pr_info("[%7d] %5d %5d %8lu %8lu %8ld %8lu         %5hd %s\n",
421                         task->pid, from_kuid(&init_user_ns, task_uid(task)),
422                         task->tgid, task->mm->total_vm, get_mm_rss(task->mm),
423                         mm_pgtables_bytes(task->mm),
424                         get_mm_counter(task->mm, MM_SWAPENTS),
425                         task->signal->oom_score_adj, task->comm);
426                 task_unlock(task);
427         }
428         rcu_read_unlock();
429 }
430 
431 static void dump_oom_summary(struct oom_control *oc, struct task_struct *victim)
432 {
433         /* one line summary of the oom killer context. */
434         pr_info("oom-kill:constraint=%s,nodemask=%*pbl",
435                         oom_constraint_text[oc->constraint],
436                         nodemask_pr_args(oc->nodemask));
437         cpuset_print_current_mems_allowed();
438         mem_cgroup_print_oom_context(oc->memcg, victim);
439         pr_cont(",task=%s,pid=%d,uid=%d\n", victim->comm, victim->pid,
440                 from_kuid(&init_user_ns, task_uid(victim)));
441 }
442 
443 static void dump_header(struct oom_control *oc, struct task_struct *p)
444 {
445         pr_warn("%s invoked oom-killer: gfp_mask=%#x(%pGg), order=%d, oom_score_adj=%hd\n",
446                 current->comm, oc->gfp_mask, &oc->gfp_mask, oc->order,
447                         current->signal->oom_score_adj);
448         if (!IS_ENABLED(CONFIG_COMPACTION) && oc->order)
449                 pr_warn("COMPACTION is disabled!!!\n");
450 
451         dump_stack();
452         if (is_memcg_oom(oc))
453                 mem_cgroup_print_oom_meminfo(oc->memcg);
454         else {
455                 show_mem(SHOW_MEM_FILTER_NODES, oc->nodemask);
456                 if (is_dump_unreclaim_slabs())
457                         dump_unreclaimable_slab();
458         }
459         if (sysctl_oom_dump_tasks)
460                 dump_tasks(oc->memcg, oc->nodemask);
461         if (p)
462                 dump_oom_summary(oc, p);
463 }
464 
465 /*
466  * Number of OOM victims in flight
467  */
468 static atomic_t oom_victims = ATOMIC_INIT(0);
469 static DECLARE_WAIT_QUEUE_HEAD(oom_victims_wait);
470 
471 static bool oom_killer_disabled __read_mostly;
472 
473 #define K(x) ((x) << (PAGE_SHIFT-10))
474 
475 /*
476  * task->mm can be NULL if the task is the exited group leader.  So to
477  * determine whether the task is using a particular mm, we examine all the
478  * task's threads: if one of those is using this mm then this task was also
479  * using it.
480  */
481 bool process_shares_mm(struct task_struct *p, struct mm_struct *mm)
482 {
483         struct task_struct *t;
484 
485         for_each_thread(p, t) {
486                 struct mm_struct *t_mm = READ_ONCE(t->mm);
487                 if (t_mm)
488                         return t_mm == mm;
489         }
490         return false;
491 }
492 
493 #ifdef CONFIG_MMU
494 /*
495  * OOM Reaper kernel thread which tries to reap the memory used by the OOM
496  * victim (if that is possible) to help the OOM killer to move on.
497  */
498 static struct task_struct *oom_reaper_th;
499 static DECLARE_WAIT_QUEUE_HEAD(oom_reaper_wait);
500 static struct task_struct *oom_reaper_list;
501 static DEFINE_SPINLOCK(oom_reaper_lock);
502 
503 bool __oom_reap_task_mm(struct mm_struct *mm)
504 {
505         struct vm_area_struct *vma;
506         bool ret = true;
507 
508         /*
509          * Tell all users of get_user/copy_from_user etc... that the content
510          * is no longer stable. No barriers really needed because unmapping
511          * should imply barriers already and the reader would hit a page fault
512          * if it stumbled over a reaped memory.
513          */
514         set_bit(MMF_UNSTABLE, &mm->flags);
515 
516         for (vma = mm->mmap ; vma; vma = vma->vm_next) {
517                 if (!can_madv_dontneed_vma(vma))
518                         continue;
519 
520                 /*
521                  * Only anonymous pages have a good chance to be dropped
522                  * without additional steps which we cannot afford as we
523                  * are OOM already.
524                  *
525                  * We do not even care about fs backed pages because all
526                  * which are reclaimable have already been reclaimed and
527                  * we do not want to block exit_mmap by keeping mm ref
528                  * count elevated without a good reason.
529                  */
530                 if (vma_is_anonymous(vma) || !(vma->vm_flags & VM_SHARED)) {
531                         struct mmu_notifier_range range;
532                         struct mmu_gather tlb;
533 
534                         mmu_notifier_range_init(&range, mm, vma->vm_start,
535                                                 vma->vm_end);
536                         tlb_gather_mmu(&tlb, mm, range.start, range.end);
537                         if (mmu_notifier_invalidate_range_start_nonblock(&range)) {
538                                 tlb_finish_mmu(&tlb, range.start, range.end);
539                                 ret = false;
540                                 continue;
541                         }
542                         unmap_page_range(&tlb, vma, range.start, range.end, NULL);
543                         mmu_notifier_invalidate_range_end(&range);
544                         tlb_finish_mmu(&tlb, range.start, range.end);
545                 }
546         }
547 
548         return ret;
549 }
550 
551 /*
552  * Reaps the address space of the give task.
553  *
554  * Returns true on success and false if none or part of the address space
555  * has been reclaimed and the caller should retry later.
556  */
557 static bool oom_reap_task_mm(struct task_struct *tsk, struct mm_struct *mm)
558 {
559         bool ret = true;
560 
561         if (!down_read_trylock(&mm->mmap_sem)) {
562                 trace_skip_task_reaping(tsk->pid);
563                 return false;
564         }
565 
566         /*
567          * MMF_OOM_SKIP is set by exit_mmap when the OOM reaper can't
568          * work on the mm anymore. The check for MMF_OOM_SKIP must run
569          * under mmap_sem for reading because it serializes against the
570          * down_write();up_write() cycle in exit_mmap().
571          */
572         if (test_bit(MMF_OOM_SKIP, &mm->flags)) {
573                 trace_skip_task_reaping(tsk->pid);
574                 goto out_unlock;
575         }
576 
577         trace_start_task_reaping(tsk->pid);
578 
579         /* failed to reap part of the address space. Try again later */
580         ret = __oom_reap_task_mm(mm);
581         if (!ret)
582                 goto out_finish;
583 
584         pr_info("oom_reaper: reaped process %d (%s), now anon-rss:%lukB, file-rss:%lukB, shmem-rss:%lukB\n",
585                         task_pid_nr(tsk), tsk->comm,
586                         K(get_mm_counter(mm, MM_ANONPAGES)),
587                         K(get_mm_counter(mm, MM_FILEPAGES)),
588                         K(get_mm_counter(mm, MM_SHMEMPAGES)));
589 out_finish:
590         trace_finish_task_reaping(tsk->pid);
591 out_unlock:
592         up_read(&mm->mmap_sem);
593 
594         return ret;
595 }
596 
597 #define MAX_OOM_REAP_RETRIES 10
598 static void oom_reap_task(struct task_struct *tsk)
599 {
600         int attempts = 0;
601         struct mm_struct *mm = tsk->signal->oom_mm;
602 
603         /* Retry the down_read_trylock(mmap_sem) a few times */
604         while (attempts++ < MAX_OOM_REAP_RETRIES && !oom_reap_task_mm(tsk, mm))
605                 schedule_timeout_idle(HZ/10);
606 
607         if (attempts <= MAX_OOM_REAP_RETRIES ||
608             test_bit(MMF_OOM_SKIP, &mm->flags))
609                 goto done;
610 
611         pr_info("oom_reaper: unable to reap pid:%d (%s)\n",
612                 task_pid_nr(tsk), tsk->comm);
613         debug_show_all_locks();
614 
615 done:
616         tsk->oom_reaper_list = NULL;
617 
618         /*
619          * Hide this mm from OOM killer because it has been either reaped or
620          * somebody can't call up_write(mmap_sem).
621          */
622         set_bit(MMF_OOM_SKIP, &mm->flags);
623 
624         /* Drop a reference taken by wake_oom_reaper */
625         put_task_struct(tsk);
626 }
627 
628 static int oom_reaper(void *unused)
629 {
630         while (true) {
631                 struct task_struct *tsk = NULL;
632 
633                 wait_event_freezable(oom_reaper_wait, oom_reaper_list != NULL);
634                 spin_lock(&oom_reaper_lock);
635                 if (oom_reaper_list != NULL) {
636                         tsk = oom_reaper_list;
637                         oom_reaper_list = tsk->oom_reaper_list;
638                 }
639                 spin_unlock(&oom_reaper_lock);
640 
641                 if (tsk)
642                         oom_reap_task(tsk);
643         }
644 
645         return 0;
646 }
647 
648 static void wake_oom_reaper(struct task_struct *tsk)
649 {
650         /* mm is already queued? */
651         if (test_and_set_bit(MMF_OOM_REAP_QUEUED, &tsk->signal->oom_mm->flags))
652                 return;
653 
654         get_task_struct(tsk);
655 
656         spin_lock(&oom_reaper_lock);
657         tsk->oom_reaper_list = oom_reaper_list;
658         oom_reaper_list = tsk;
659         spin_unlock(&oom_reaper_lock);
660         trace_wake_reaper(tsk->pid);
661         wake_up(&oom_reaper_wait);
662 }
663 
664 static int __init oom_init(void)
665 {
666         oom_reaper_th = kthread_run(oom_reaper, NULL, "oom_reaper");
667         return 0;
668 }
669 subsys_initcall(oom_init)
670 #else
671 static inline void wake_oom_reaper(struct task_struct *tsk)
672 {
673 }
674 #endif /* CONFIG_MMU */
675 
676 /**
677  * mark_oom_victim - mark the given task as OOM victim
678  * @tsk: task to mark
679  *
680  * Has to be called with oom_lock held and never after
681  * oom has been disabled already.
682  *
683  * tsk->mm has to be non NULL and caller has to guarantee it is stable (either
684  * under task_lock or operate on the current).
685  */
686 static void mark_oom_victim(struct task_struct *tsk)
687 {
688         struct mm_struct *mm = tsk->mm;
689 
690         WARN_ON(oom_killer_disabled);
691         /* OOM killer might race with memcg OOM */
692         if (test_and_set_tsk_thread_flag(tsk, TIF_MEMDIE))
693                 return;
694 
695         /* oom_mm is bound to the signal struct life time. */
696         if (!cmpxchg(&tsk->signal->oom_mm, NULL, mm)) {
697                 mmgrab(tsk->signal->oom_mm);
698                 set_bit(MMF_OOM_VICTIM, &mm->flags);
699         }
700 
701         /*
702          * Make sure that the task is woken up from uninterruptible sleep
703          * if it is frozen because OOM killer wouldn't be able to free
704          * any memory and livelock. freezing_slow_path will tell the freezer
705          * that TIF_MEMDIE tasks should be ignored.
706          */
707         __thaw_task(tsk);
708         atomic_inc(&oom_victims);
709         trace_mark_victim(tsk->pid);
710 }
711 
712 /**
713  * exit_oom_victim - note the exit of an OOM victim
714  */
715 void exit_oom_victim(void)
716 {
717         clear_thread_flag(TIF_MEMDIE);
718 
719         if (!atomic_dec_return(&oom_victims))
720                 wake_up_all(&oom_victims_wait);
721 }
722 
723 /**
724  * oom_killer_enable - enable OOM killer
725  */
726 void oom_killer_enable(void)
727 {
728         oom_killer_disabled = false;
729         pr_info("OOM killer enabled.\n");
730 }
731 
732 /**
733  * oom_killer_disable - disable OOM killer
734  * @timeout: maximum timeout to wait for oom victims in jiffies
735  *
736  * Forces all page allocations to fail rather than trigger OOM killer.
737  * Will block and wait until all OOM victims are killed or the given
738  * timeout expires.
739  *
740  * The function cannot be called when there are runnable user tasks because
741  * the userspace would see unexpected allocation failures as a result. Any
742  * new usage of this function should be consulted with MM people.
743  *
744  * Returns true if successful and false if the OOM killer cannot be
745  * disabled.
746  */
747 bool oom_killer_disable(signed long timeout)
748 {
749         signed long ret;
750 
751         /*
752          * Make sure to not race with an ongoing OOM killer. Check that the
753          * current is not killed (possibly due to sharing the victim's memory).
754          */
755         if (mutex_lock_killable(&oom_lock))
756                 return false;
757         oom_killer_disabled = true;
758         mutex_unlock(&oom_lock);
759 
760         ret = wait_event_interruptible_timeout(oom_victims_wait,
761                         !atomic_read(&oom_victims), timeout);
762         if (ret <= 0) {
763                 oom_killer_enable();
764                 return false;
765         }
766         pr_info("OOM killer disabled.\n");
767 
768         return true;
769 }
770 
771 static inline bool __task_will_free_mem(struct task_struct *task)
772 {
773         struct signal_struct *sig = task->signal;
774 
775         /*
776          * A coredumping process may sleep for an extended period in exit_mm(),
777          * so the oom killer cannot assume that the process will promptly exit
778          * and release memory.
779          */
780         if (sig->flags & SIGNAL_GROUP_COREDUMP)
781                 return false;
782 
783         if (sig->flags & SIGNAL_GROUP_EXIT)
784                 return true;
785 
786         if (thread_group_empty(task) && (task->flags & PF_EXITING))
787                 return true;
788 
789         return false;
790 }
791 
792 /*
793  * Checks whether the given task is dying or exiting and likely to
794  * release its address space. This means that all threads and processes
795  * sharing the same mm have to be killed or exiting.
796  * Caller has to make sure that task->mm is stable (hold task_lock or
797  * it operates on the current).
798  */
799 static bool task_will_free_mem(struct task_struct *task)
800 {
801         struct mm_struct *mm = task->mm;
802         struct task_struct *p;
803         bool ret = true;
804 
805         /*
806          * Skip tasks without mm because it might have passed its exit_mm and
807          * exit_oom_victim. oom_reaper could have rescued that but do not rely
808          * on that for now. We can consider find_lock_task_mm in future.
809          */
810         if (!mm)
811                 return false;
812 
813         if (!__task_will_free_mem(task))
814                 return false;
815 
816         /*
817          * This task has already been drained by the oom reaper so there are
818          * only small chances it will free some more
819          */
820         if (test_bit(MMF_OOM_SKIP, &mm->flags))
821                 return false;
822 
823         if (atomic_read(&mm->mm_users) <= 1)
824                 return true;
825 
826         /*
827          * Make sure that all tasks which share the mm with the given tasks
828          * are dying as well to make sure that a) nobody pins its mm and
829          * b) the task is also reapable by the oom reaper.
830          */
831         rcu_read_lock();
832         for_each_process(p) {
833                 if (!process_shares_mm(p, mm))
834                         continue;
835                 if (same_thread_group(task, p))
836                         continue;
837                 ret = __task_will_free_mem(p);
838                 if (!ret)
839                         break;
840         }
841         rcu_read_unlock();
842 
843         return ret;
844 }
845 
846 static void __oom_kill_process(struct task_struct *victim, const char *message)
847 {
848         struct task_struct *p;
849         struct mm_struct *mm;
850         bool can_oom_reap = true;
851 
852         p = find_lock_task_mm(victim);
853         if (!p) {
854                 put_task_struct(victim);
855                 return;
856         } else if (victim != p) {
857                 get_task_struct(p);
858                 put_task_struct(victim);
859                 victim = p;
860         }
861 
862         /* Get a reference to safely compare mm after task_unlock(victim) */
863         mm = victim->mm;
864         mmgrab(mm);
865 
866         /* Raise event before sending signal: task reaper must see this */
867         count_vm_event(OOM_KILL);
868         memcg_memory_event_mm(mm, MEMCG_OOM_KILL);
869 
870         /*
871          * We should send SIGKILL before granting access to memory reserves
872          * in order to prevent the OOM victim from depleting the memory
873          * reserves from the user space under its control.
874          */
875         do_send_sig_info(SIGKILL, SEND_SIG_PRIV, victim, PIDTYPE_TGID);
876         mark_oom_victim(victim);
877         pr_err("%s: Killed process %d (%s) total-vm:%lukB, anon-rss:%lukB, file-rss:%lukB, shmem-rss:%lukB\n",
878                 message, task_pid_nr(victim), victim->comm,
879                 K(victim->mm->total_vm),
880                 K(get_mm_counter(victim->mm, MM_ANONPAGES)),
881                 K(get_mm_counter(victim->mm, MM_FILEPAGES)),
882                 K(get_mm_counter(victim->mm, MM_SHMEMPAGES)));
883         task_unlock(victim);
884 
885         /*
886          * Kill all user processes sharing victim->mm in other thread groups, if
887          * any.  They don't get access to memory reserves, though, to avoid
888          * depletion of all memory.  This prevents mm->mmap_sem livelock when an
889          * oom killed thread cannot exit because it requires the semaphore and
890          * its contended by another thread trying to allocate memory itself.
891          * That thread will now get access to memory reserves since it has a
892          * pending fatal signal.
893          */
894         rcu_read_lock();
895         for_each_process(p) {
896                 if (!process_shares_mm(p, mm))
897                         continue;
898                 if (same_thread_group(p, victim))
899                         continue;
900                 if (is_global_init(p)) {
901                         can_oom_reap = false;
902                         set_bit(MMF_OOM_SKIP, &mm->flags);
903                         pr_info("oom killer %d (%s) has mm pinned by %d (%s)\n",
904                                         task_pid_nr(victim), victim->comm,
905                                         task_pid_nr(p), p->comm);
906                         continue;
907                 }
908                 /*
909                  * No use_mm() user needs to read from the userspace so we are
910                  * ok to reap it.
911                  */
912                 if (unlikely(p->flags & PF_KTHREAD))
913                         continue;
914                 do_send_sig_info(SIGKILL, SEND_SIG_PRIV, p, PIDTYPE_TGID);
915         }
916         rcu_read_unlock();
917 
918         if (can_oom_reap)
919                 wake_oom_reaper(victim);
920 
921         mmdrop(mm);
922         put_task_struct(victim);
923 }
924 #undef K
925 
926 /*
927  * Kill provided task unless it's secured by setting
928  * oom_score_adj to OOM_SCORE_ADJ_MIN.
929  */
930 static int oom_kill_memcg_member(struct task_struct *task, void *message)
931 {
932         if (task->signal->oom_score_adj != OOM_SCORE_ADJ_MIN &&
933             !is_global_init(task)) {
934                 get_task_struct(task);
935                 __oom_kill_process(task, message);
936         }
937         return 0;
938 }
939 
940 static void oom_kill_process(struct oom_control *oc, const char *message)
941 {
942         struct task_struct *victim = oc->chosen;
943         struct mem_cgroup *oom_group;
944         static DEFINE_RATELIMIT_STATE(oom_rs, DEFAULT_RATELIMIT_INTERVAL,
945                                               DEFAULT_RATELIMIT_BURST);
946 
947         /*
948          * If the task is already exiting, don't alarm the sysadmin or kill
949          * its children or threads, just give it access to memory reserves
950          * so it can die quickly
951          */
952         task_lock(victim);
953         if (task_will_free_mem(victim)) {
954                 mark_oom_victim(victim);
955                 wake_oom_reaper(victim);
956                 task_unlock(victim);
957                 put_task_struct(victim);
958                 return;
959         }
960         task_unlock(victim);
961 
962         if (__ratelimit(&oom_rs))
963                 dump_header(oc, victim);
964 
965         /*
966          * Do we need to kill the entire memory cgroup?
967          * Or even one of the ancestor memory cgroups?
968          * Check this out before killing the victim task.
969          */
970         oom_group = mem_cgroup_get_oom_group(victim, oc->memcg);
971 
972         __oom_kill_process(victim, message);
973 
974         /*
975          * If necessary, kill all tasks in the selected memory cgroup.
976          */
977         if (oom_group) {
978                 mem_cgroup_print_oom_group(oom_group);
979                 mem_cgroup_scan_tasks(oom_group, oom_kill_memcg_member,
980                                       (void*)message);
981                 mem_cgroup_put(oom_group);
982         }
983 }
984 
985 /*
986  * Determines whether the kernel must panic because of the panic_on_oom sysctl.
987  */
988 static void check_panic_on_oom(struct oom_control *oc)
989 {
990         if (likely(!sysctl_panic_on_oom))
991                 return;
992         if (sysctl_panic_on_oom != 2) {
993                 /*
994                  * panic_on_oom == 1 only affects CONSTRAINT_NONE, the kernel
995                  * does not panic for cpuset, mempolicy, or memcg allocation
996                  * failures.
997                  */
998                 if (oc->constraint != CONSTRAINT_NONE)
999                         return;
1000         }
1001         /* Do not panic for oom kills triggered by sysrq */
1002         if (is_sysrq_oom(oc))
1003                 return;
1004         dump_header(oc, NULL);
1005         panic("Out of memory: %s panic_on_oom is enabled\n",
1006                 sysctl_panic_on_oom == 2 ? "compulsory" : "system-wide");
1007 }
1008 
1009 static BLOCKING_NOTIFIER_HEAD(oom_notify_list);
1010 
1011 int register_oom_notifier(struct notifier_block *nb)
1012 {
1013         return blocking_notifier_chain_register(&oom_notify_list, nb);
1014 }
1015 EXPORT_SYMBOL_GPL(register_oom_notifier);
1016 
1017 int unregister_oom_notifier(struct notifier_block *nb)
1018 {
1019         return blocking_notifier_chain_unregister(&oom_notify_list, nb);
1020 }
1021 EXPORT_SYMBOL_GPL(unregister_oom_notifier);
1022 
1023 /**
1024  * out_of_memory - kill the "best" process when we run out of memory
1025  * @oc: pointer to struct oom_control
1026  *
1027  * If we run out of memory, we have the choice between either
1028  * killing a random task (bad), letting the system crash (worse)
1029  * OR try to be smart about which process to kill. Note that we
1030  * don't have to be perfect here, we just have to be good.
1031  */
1032 bool out_of_memory(struct oom_control *oc)
1033 {
1034         unsigned long freed = 0;
1035 
1036         if (oom_killer_disabled)
1037                 return false;
1038 
1039         if (!is_memcg_oom(oc)) {
1040                 blocking_notifier_call_chain(&oom_notify_list, 0, &freed);
1041                 if (freed > 0)
1042                         /* Got some memory back in the last second. */
1043                         return true;
1044         }
1045 
1046         /*
1047          * If current has a pending SIGKILL or is exiting, then automatically
1048          * select it.  The goal is to allow it to allocate so that it may
1049          * quickly exit and free its memory.
1050          */
1051         if (task_will_free_mem(current)) {
1052                 mark_oom_victim(current);
1053                 wake_oom_reaper(current);
1054                 return true;
1055         }
1056 
1057         /*
1058          * The OOM killer does not compensate for IO-less reclaim.
1059          * pagefault_out_of_memory lost its gfp context so we have to
1060          * make sure exclude 0 mask - all other users should have at least
1061          * ___GFP_DIRECT_RECLAIM to get here.
1062          */
1063         if (oc->gfp_mask && !(oc->gfp_mask & __GFP_FS))
1064                 return true;
1065 
1066         /*
1067          * Check if there were limitations on the allocation (only relevant for
1068          * NUMA and memcg) that may require different handling.
1069          */
1070         oc->constraint = constrained_alloc(oc);
1071         if (oc->constraint != CONSTRAINT_MEMORY_POLICY)
1072                 oc->nodemask = NULL;
1073         check_panic_on_oom(oc);
1074 
1075         if (!is_memcg_oom(oc) && sysctl_oom_kill_allocating_task &&
1076             current->mm && !oom_unkillable_task(current, NULL, oc->nodemask) &&
1077             current->signal->oom_score_adj != OOM_SCORE_ADJ_MIN) {
1078                 get_task_struct(current);
1079                 oc->chosen = current;
1080                 oom_kill_process(oc, "Out of memory (oom_kill_allocating_task)");
1081                 return true;
1082         }
1083 
1084         select_bad_process(oc);
1085         /* Found nothing?!?! */
1086         if (!oc->chosen) {
1087                 dump_header(oc, NULL);
1088                 pr_warn("Out of memory and no killable processes...\n");
1089                 /*
1090                  * If we got here due to an actual allocation at the
1091                  * system level, we cannot survive this and will enter
1092                  * an endless loop in the allocator. Bail out now.
1093                  */
1094                 if (!is_sysrq_oom(oc) && !is_memcg_oom(oc))
1095                         panic("System is deadlocked on memory\n");
1096         }
1097         if (oc->chosen && oc->chosen != (void *)-1UL)
1098                 oom_kill_process(oc, !is_memcg_oom(oc) ? "Out of memory" :
1099                                  "Memory cgroup out of memory");
1100         return !!oc->chosen;
1101 }
1102 
1103 /*
1104  * The pagefault handler calls here because it is out of memory, so kill a
1105  * memory-hogging task. If oom_lock is held by somebody else, a parallel oom
1106  * killing is already in progress so do nothing.
1107  */
1108 void pagefault_out_of_memory(void)
1109 {
1110         struct oom_control oc = {
1111                 .zonelist = NULL,
1112                 .nodemask = NULL,
1113                 .memcg = NULL,
1114                 .gfp_mask = 0,
1115                 .order = 0,
1116         };
1117 
1118         if (mem_cgroup_oom_synchronize(true))
1119                 return;
1120 
1121         if (!mutex_trylock(&oom_lock))
1122                 return;
1123         out_of_memory(&oc);
1124         mutex_unlock(&oom_lock);
1125 }
1126 

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