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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/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 
 39 #define CREATE_TRACE_POINTS
 40 #include <trace/events/oom.h>
 41 
 42 int sysctl_panic_on_oom;
 43 int sysctl_oom_kill_allocating_task;
 44 int sysctl_oom_dump_tasks = 1;
 45 static DEFINE_SPINLOCK(zone_scan_lock);
 46 
 47 #ifdef CONFIG_NUMA
 48 /**
 49  * has_intersects_mems_allowed() - check task eligiblity for kill
 50  * @start: task struct of which task to consider
 51  * @mask: nodemask passed to page allocator for mempolicy ooms
 52  *
 53  * Task eligibility is determined by whether or not a candidate task, @tsk,
 54  * shares the same mempolicy nodes as current if it is bound by such a policy
 55  * and whether or not it has the same set of allowed cpuset nodes.
 56  */
 57 static bool has_intersects_mems_allowed(struct task_struct *start,
 58                                         const nodemask_t *mask)
 59 {
 60         struct task_struct *tsk;
 61         bool ret = false;
 62 
 63         rcu_read_lock();
 64         for_each_thread(start, tsk) {
 65                 if (mask) {
 66                         /*
 67                          * If this is a mempolicy constrained oom, tsk's
 68                          * cpuset is irrelevant.  Only return true if its
 69                          * mempolicy intersects current, otherwise it may be
 70                          * needlessly killed.
 71                          */
 72                         ret = mempolicy_nodemask_intersects(tsk, mask);
 73                 } else {
 74                         /*
 75                          * This is not a mempolicy constrained oom, so only
 76                          * check the mems of tsk's cpuset.
 77                          */
 78                         ret = cpuset_mems_allowed_intersects(current, tsk);
 79                 }
 80                 if (ret)
 81                         break;
 82         }
 83         rcu_read_unlock();
 84 
 85         return ret;
 86 }
 87 #else
 88 static bool has_intersects_mems_allowed(struct task_struct *tsk,
 89                                         const nodemask_t *mask)
 90 {
 91         return true;
 92 }
 93 #endif /* CONFIG_NUMA */
 94 
 95 /*
 96  * The process p may have detached its own ->mm while exiting or through
 97  * use_mm(), but one or more of its subthreads may still have a valid
 98  * pointer.  Return p, or any of its subthreads with a valid ->mm, with
 99  * task_lock() held.
100  */
101 struct task_struct *find_lock_task_mm(struct task_struct *p)
102 {
103         struct task_struct *t;
104 
105         rcu_read_lock();
106 
107         for_each_thread(p, t) {
108                 task_lock(t);
109                 if (likely(t->mm))
110                         goto found;
111                 task_unlock(t);
112         }
113         t = NULL;
114 found:
115         rcu_read_unlock();
116 
117         return t;
118 }
119 
120 /* return true if the task is not adequate as candidate victim task. */
121 static bool oom_unkillable_task(struct task_struct *p,
122                 struct mem_cgroup *memcg, const nodemask_t *nodemask)
123 {
124         if (is_global_init(p))
125                 return true;
126         if (p->flags & PF_KTHREAD)
127                 return true;
128 
129         /* When mem_cgroup_out_of_memory() and p is not member of the group */
130         if (memcg && !task_in_mem_cgroup(p, memcg))
131                 return true;
132 
133         /* p may not have freeable memory in nodemask */
134         if (!has_intersects_mems_allowed(p, nodemask))
135                 return true;
136 
137         return false;
138 }
139 
140 /**
141  * oom_badness - heuristic function to determine which candidate task to kill
142  * @p: task struct of which task we should calculate
143  * @totalpages: total present RAM allowed for page allocation
144  *
145  * The heuristic for determining which task to kill is made to be as simple and
146  * predictable as possible.  The goal is to return the highest value for the
147  * task consuming the most memory to avoid subsequent oom failures.
148  */
149 unsigned long oom_badness(struct task_struct *p, struct mem_cgroup *memcg,
150                           const nodemask_t *nodemask, unsigned long totalpages)
151 {
152         long points;
153         long adj;
154 
155         if (oom_unkillable_task(p, memcg, nodemask))
156                 return 0;
157 
158         p = find_lock_task_mm(p);
159         if (!p)
160                 return 0;
161 
162         adj = (long)p->signal->oom_score_adj;
163         if (adj == OOM_SCORE_ADJ_MIN) {
164                 task_unlock(p);
165                 return 0;
166         }
167 
168         /*
169          * The baseline for the badness score is the proportion of RAM that each
170          * task's rss, pagetable and swap space use.
171          */
172         points = get_mm_rss(p->mm) + get_mm_counter(p->mm, MM_SWAPENTS) +
173                 atomic_long_read(&p->mm->nr_ptes) + mm_nr_pmds(p->mm);
174         task_unlock(p);
175 
176         /*
177          * Root processes get 3% bonus, just like the __vm_enough_memory()
178          * implementation used by LSMs.
179          */
180         if (has_capability_noaudit(p, CAP_SYS_ADMIN))
181                 points -= (points * 3) / 100;
182 
183         /* Normalize to oom_score_adj units */
184         adj *= totalpages / 1000;
185         points += adj;
186 
187         /*
188          * Never return 0 for an eligible task regardless of the root bonus and
189          * oom_score_adj (oom_score_adj can't be OOM_SCORE_ADJ_MIN here).
190          */
191         return points > 0 ? points : 1;
192 }
193 
194 /*
195  * Determine the type of allocation constraint.
196  */
197 #ifdef CONFIG_NUMA
198 static enum oom_constraint constrained_alloc(struct zonelist *zonelist,
199                                 gfp_t gfp_mask, nodemask_t *nodemask,
200                                 unsigned long *totalpages)
201 {
202         struct zone *zone;
203         struct zoneref *z;
204         enum zone_type high_zoneidx = gfp_zone(gfp_mask);
205         bool cpuset_limited = false;
206         int nid;
207 
208         /* Default to all available memory */
209         *totalpages = totalram_pages + total_swap_pages;
210 
211         if (!zonelist)
212                 return CONSTRAINT_NONE;
213         /*
214          * Reach here only when __GFP_NOFAIL is used. So, we should avoid
215          * to kill current.We have to random task kill in this case.
216          * Hopefully, CONSTRAINT_THISNODE...but no way to handle it, now.
217          */
218         if (gfp_mask & __GFP_THISNODE)
219                 return CONSTRAINT_NONE;
220 
221         /*
222          * This is not a __GFP_THISNODE allocation, so a truncated nodemask in
223          * the page allocator means a mempolicy is in effect.  Cpuset policy
224          * is enforced in get_page_from_freelist().
225          */
226         if (nodemask && !nodes_subset(node_states[N_MEMORY], *nodemask)) {
227                 *totalpages = total_swap_pages;
228                 for_each_node_mask(nid, *nodemask)
229                         *totalpages += node_spanned_pages(nid);
230                 return CONSTRAINT_MEMORY_POLICY;
231         }
232 
233         /* Check this allocation failure is caused by cpuset's wall function */
234         for_each_zone_zonelist_nodemask(zone, z, zonelist,
235                         high_zoneidx, nodemask)
236                 if (!cpuset_zone_allowed(zone, gfp_mask))
237                         cpuset_limited = true;
238 
239         if (cpuset_limited) {
240                 *totalpages = total_swap_pages;
241                 for_each_node_mask(nid, cpuset_current_mems_allowed)
242                         *totalpages += node_spanned_pages(nid);
243                 return CONSTRAINT_CPUSET;
244         }
245         return CONSTRAINT_NONE;
246 }
247 #else
248 static enum oom_constraint constrained_alloc(struct zonelist *zonelist,
249                                 gfp_t gfp_mask, nodemask_t *nodemask,
250                                 unsigned long *totalpages)
251 {
252         *totalpages = totalram_pages + total_swap_pages;
253         return CONSTRAINT_NONE;
254 }
255 #endif
256 
257 enum oom_scan_t oom_scan_process_thread(struct task_struct *task,
258                 unsigned long totalpages, const nodemask_t *nodemask,
259                 bool force_kill)
260 {
261         if (oom_unkillable_task(task, NULL, nodemask))
262                 return OOM_SCAN_CONTINUE;
263 
264         /*
265          * This task already has access to memory reserves and is being killed.
266          * Don't allow any other task to have access to the reserves.
267          */
268         if (test_tsk_thread_flag(task, TIF_MEMDIE)) {
269                 if (!force_kill)
270                         return OOM_SCAN_ABORT;
271         }
272         if (!task->mm)
273                 return OOM_SCAN_CONTINUE;
274 
275         /*
276          * If task is allocating a lot of memory and has been marked to be
277          * killed first if it triggers an oom, then select it.
278          */
279         if (oom_task_origin(task))
280                 return OOM_SCAN_SELECT;
281 
282         if (task_will_free_mem(task) && !force_kill)
283                 return OOM_SCAN_ABORT;
284 
285         return OOM_SCAN_OK;
286 }
287 
288 /*
289  * Simple selection loop. We chose the process with the highest
290  * number of 'points'.  Returns -1 on scan abort.
291  *
292  * (not docbooked, we don't want this one cluttering up the manual)
293  */
294 static struct task_struct *select_bad_process(unsigned int *ppoints,
295                 unsigned long totalpages, const nodemask_t *nodemask,
296                 bool force_kill)
297 {
298         struct task_struct *g, *p;
299         struct task_struct *chosen = NULL;
300         unsigned long chosen_points = 0;
301 
302         rcu_read_lock();
303         for_each_process_thread(g, p) {
304                 unsigned int points;
305 
306                 switch (oom_scan_process_thread(p, totalpages, nodemask,
307                                                 force_kill)) {
308                 case OOM_SCAN_SELECT:
309                         chosen = p;
310                         chosen_points = ULONG_MAX;
311                         /* fall through */
312                 case OOM_SCAN_CONTINUE:
313                         continue;
314                 case OOM_SCAN_ABORT:
315                         rcu_read_unlock();
316                         return (struct task_struct *)(-1UL);
317                 case OOM_SCAN_OK:
318                         break;
319                 };
320                 points = oom_badness(p, NULL, nodemask, totalpages);
321                 if (!points || points < chosen_points)
322                         continue;
323                 /* Prefer thread group leaders for display purposes */
324                 if (points == chosen_points && thread_group_leader(chosen))
325                         continue;
326 
327                 chosen = p;
328                 chosen_points = points;
329         }
330         if (chosen)
331                 get_task_struct(chosen);
332         rcu_read_unlock();
333 
334         *ppoints = chosen_points * 1000 / totalpages;
335         return chosen;
336 }
337 
338 /**
339  * dump_tasks - dump current memory state of all system tasks
340  * @memcg: current's memory controller, if constrained
341  * @nodemask: nodemask passed to page allocator for mempolicy ooms
342  *
343  * Dumps the current memory state of all eligible tasks.  Tasks not in the same
344  * memcg, not in the same cpuset, or bound to a disjoint set of mempolicy nodes
345  * are not shown.
346  * State information includes task's pid, uid, tgid, vm size, rss, nr_ptes,
347  * swapents, oom_score_adj value, and name.
348  */
349 static void dump_tasks(struct mem_cgroup *memcg, const nodemask_t *nodemask)
350 {
351         struct task_struct *p;
352         struct task_struct *task;
353 
354         pr_info("[ pid ]   uid  tgid total_vm      rss nr_ptes nr_pmds swapents oom_score_adj name\n");
355         rcu_read_lock();
356         for_each_process(p) {
357                 if (oom_unkillable_task(p, memcg, nodemask))
358                         continue;
359 
360                 task = find_lock_task_mm(p);
361                 if (!task) {
362                         /*
363                          * This is a kthread or all of p's threads have already
364                          * detached their mm's.  There's no need to report
365                          * them; they can't be oom killed anyway.
366                          */
367                         continue;
368                 }
369 
370                 pr_info("[%5d] %5d %5d %8lu %8lu %7ld %7ld %8lu         %5hd %s\n",
371                         task->pid, from_kuid(&init_user_ns, task_uid(task)),
372                         task->tgid, task->mm->total_vm, get_mm_rss(task->mm),
373                         atomic_long_read(&task->mm->nr_ptes),
374                         mm_nr_pmds(task->mm),
375                         get_mm_counter(task->mm, MM_SWAPENTS),
376                         task->signal->oom_score_adj, task->comm);
377                 task_unlock(task);
378         }
379         rcu_read_unlock();
380 }
381 
382 static void dump_header(struct task_struct *p, gfp_t gfp_mask, int order,
383                         struct mem_cgroup *memcg, const nodemask_t *nodemask)
384 {
385         task_lock(current);
386         pr_warning("%s invoked oom-killer: gfp_mask=0x%x, order=%d, "
387                 "oom_score_adj=%hd\n",
388                 current->comm, gfp_mask, order,
389                 current->signal->oom_score_adj);
390         cpuset_print_task_mems_allowed(current);
391         task_unlock(current);
392         dump_stack();
393         if (memcg)
394                 mem_cgroup_print_oom_info(memcg, p);
395         else
396                 show_mem(SHOW_MEM_FILTER_NODES);
397         if (sysctl_oom_dump_tasks)
398                 dump_tasks(memcg, nodemask);
399 }
400 
401 /*
402  * Number of OOM victims in flight
403  */
404 static atomic_t oom_victims = ATOMIC_INIT(0);
405 static DECLARE_WAIT_QUEUE_HEAD(oom_victims_wait);
406 
407 bool oom_killer_disabled __read_mostly;
408 static DECLARE_RWSEM(oom_sem);
409 
410 /**
411  * mark_tsk_oom_victim - marks the given taks as OOM victim.
412  * @tsk: task to mark
413  *
414  * Has to be called with oom_sem taken for read and never after
415  * oom has been disabled already.
416  */
417 void mark_tsk_oom_victim(struct task_struct *tsk)
418 {
419         WARN_ON(oom_killer_disabled);
420         /* OOM killer might race with memcg OOM */
421         if (test_and_set_tsk_thread_flag(tsk, TIF_MEMDIE))
422                 return;
423         /*
424          * Make sure that the task is woken up from uninterruptible sleep
425          * if it is frozen because OOM killer wouldn't be able to free
426          * any memory and livelock. freezing_slow_path will tell the freezer
427          * that TIF_MEMDIE tasks should be ignored.
428          */
429         __thaw_task(tsk);
430         atomic_inc(&oom_victims);
431 }
432 
433 /**
434  * unmark_oom_victim - unmarks the current task as OOM victim.
435  *
436  * Wakes up all waiters in oom_killer_disable()
437  */
438 void unmark_oom_victim(void)
439 {
440         if (!test_and_clear_thread_flag(TIF_MEMDIE))
441                 return;
442 
443         down_read(&oom_sem);
444         /*
445          * There is no need to signal the lasst oom_victim if there
446          * is nobody who cares.
447          */
448         if (!atomic_dec_return(&oom_victims) && oom_killer_disabled)
449                 wake_up_all(&oom_victims_wait);
450         up_read(&oom_sem);
451 }
452 
453 /**
454  * oom_killer_disable - disable OOM killer
455  *
456  * Forces all page allocations to fail rather than trigger OOM killer.
457  * Will block and wait until all OOM victims are killed.
458  *
459  * The function cannot be called when there are runnable user tasks because
460  * the userspace would see unexpected allocation failures as a result. Any
461  * new usage of this function should be consulted with MM people.
462  *
463  * Returns true if successful and false if the OOM killer cannot be
464  * disabled.
465  */
466 bool oom_killer_disable(void)
467 {
468         /*
469          * Make sure to not race with an ongoing OOM killer
470          * and that the current is not the victim.
471          */
472         down_write(&oom_sem);
473         if (test_thread_flag(TIF_MEMDIE)) {
474                 up_write(&oom_sem);
475                 return false;
476         }
477 
478         oom_killer_disabled = true;
479         up_write(&oom_sem);
480 
481         wait_event(oom_victims_wait, !atomic_read(&oom_victims));
482 
483         return true;
484 }
485 
486 /**
487  * oom_killer_enable - enable OOM killer
488  */
489 void oom_killer_enable(void)
490 {
491         down_write(&oom_sem);
492         oom_killer_disabled = false;
493         up_write(&oom_sem);
494 }
495 
496 #define K(x) ((x) << (PAGE_SHIFT-10))
497 /*
498  * Must be called while holding a reference to p, which will be released upon
499  * returning.
500  */
501 void oom_kill_process(struct task_struct *p, gfp_t gfp_mask, int order,
502                       unsigned int points, unsigned long totalpages,
503                       struct mem_cgroup *memcg, nodemask_t *nodemask,
504                       const char *message)
505 {
506         struct task_struct *victim = p;
507         struct task_struct *child;
508         struct task_struct *t;
509         struct mm_struct *mm;
510         unsigned int victim_points = 0;
511         static DEFINE_RATELIMIT_STATE(oom_rs, DEFAULT_RATELIMIT_INTERVAL,
512                                               DEFAULT_RATELIMIT_BURST);
513 
514         /*
515          * If the task is already exiting, don't alarm the sysadmin or kill
516          * its children or threads, just set TIF_MEMDIE so it can die quickly
517          */
518         task_lock(p);
519         if (p->mm && task_will_free_mem(p)) {
520                 mark_tsk_oom_victim(p);
521                 task_unlock(p);
522                 put_task_struct(p);
523                 return;
524         }
525         task_unlock(p);
526 
527         if (__ratelimit(&oom_rs))
528                 dump_header(p, gfp_mask, order, memcg, nodemask);
529 
530         task_lock(p);
531         pr_err("%s: Kill process %d (%s) score %d or sacrifice child\n",
532                 message, task_pid_nr(p), p->comm, points);
533         task_unlock(p);
534 
535         /*
536          * If any of p's children has a different mm and is eligible for kill,
537          * the one with the highest oom_badness() score is sacrificed for its
538          * parent.  This attempts to lose the minimal amount of work done while
539          * still freeing memory.
540          */
541         read_lock(&tasklist_lock);
542         for_each_thread(p, t) {
543                 list_for_each_entry(child, &t->children, sibling) {
544                         unsigned int child_points;
545 
546                         if (child->mm == p->mm)
547                                 continue;
548                         /*
549                          * oom_badness() returns 0 if the thread is unkillable
550                          */
551                         child_points = oom_badness(child, memcg, nodemask,
552                                                                 totalpages);
553                         if (child_points > victim_points) {
554                                 put_task_struct(victim);
555                                 victim = child;
556                                 victim_points = child_points;
557                                 get_task_struct(victim);
558                         }
559                 }
560         }
561         read_unlock(&tasklist_lock);
562 
563         p = find_lock_task_mm(victim);
564         if (!p) {
565                 put_task_struct(victim);
566                 return;
567         } else if (victim != p) {
568                 get_task_struct(p);
569                 put_task_struct(victim);
570                 victim = p;
571         }
572 
573         /* mm cannot safely be dereferenced after task_unlock(victim) */
574         mm = victim->mm;
575         mark_tsk_oom_victim(victim);
576         pr_err("Killed process %d (%s) total-vm:%lukB, anon-rss:%lukB, file-rss:%lukB\n",
577                 task_pid_nr(victim), victim->comm, K(victim->mm->total_vm),
578                 K(get_mm_counter(victim->mm, MM_ANONPAGES)),
579                 K(get_mm_counter(victim->mm, MM_FILEPAGES)));
580         task_unlock(victim);
581 
582         /*
583          * Kill all user processes sharing victim->mm in other thread groups, if
584          * any.  They don't get access to memory reserves, though, to avoid
585          * depletion of all memory.  This prevents mm->mmap_sem livelock when an
586          * oom killed thread cannot exit because it requires the semaphore and
587          * its contended by another thread trying to allocate memory itself.
588          * That thread will now get access to memory reserves since it has a
589          * pending fatal signal.
590          */
591         rcu_read_lock();
592         for_each_process(p)
593                 if (p->mm == mm && !same_thread_group(p, victim) &&
594                     !(p->flags & PF_KTHREAD)) {
595                         if (p->signal->oom_score_adj == OOM_SCORE_ADJ_MIN)
596                                 continue;
597 
598                         task_lock(p);   /* Protect ->comm from prctl() */
599                         pr_err("Kill process %d (%s) sharing same memory\n",
600                                 task_pid_nr(p), p->comm);
601                         task_unlock(p);
602                         do_send_sig_info(SIGKILL, SEND_SIG_FORCED, p, true);
603                 }
604         rcu_read_unlock();
605 
606         do_send_sig_info(SIGKILL, SEND_SIG_FORCED, victim, true);
607         put_task_struct(victim);
608 }
609 #undef K
610 
611 /*
612  * Determines whether the kernel must panic because of the panic_on_oom sysctl.
613  */
614 void check_panic_on_oom(enum oom_constraint constraint, gfp_t gfp_mask,
615                         int order, const nodemask_t *nodemask)
616 {
617         if (likely(!sysctl_panic_on_oom))
618                 return;
619         if (sysctl_panic_on_oom != 2) {
620                 /*
621                  * panic_on_oom == 1 only affects CONSTRAINT_NONE, the kernel
622                  * does not panic for cpuset, mempolicy, or memcg allocation
623                  * failures.
624                  */
625                 if (constraint != CONSTRAINT_NONE)
626                         return;
627         }
628         dump_header(NULL, gfp_mask, order, NULL, nodemask);
629         panic("Out of memory: %s panic_on_oom is enabled\n",
630                 sysctl_panic_on_oom == 2 ? "compulsory" : "system-wide");
631 }
632 
633 static BLOCKING_NOTIFIER_HEAD(oom_notify_list);
634 
635 int register_oom_notifier(struct notifier_block *nb)
636 {
637         return blocking_notifier_chain_register(&oom_notify_list, nb);
638 }
639 EXPORT_SYMBOL_GPL(register_oom_notifier);
640 
641 int unregister_oom_notifier(struct notifier_block *nb)
642 {
643         return blocking_notifier_chain_unregister(&oom_notify_list, nb);
644 }
645 EXPORT_SYMBOL_GPL(unregister_oom_notifier);
646 
647 /*
648  * Try to acquire the OOM killer lock for the zones in zonelist.  Returns zero
649  * if a parallel OOM killing is already taking place that includes a zone in
650  * the zonelist.  Otherwise, locks all zones in the zonelist and returns 1.
651  */
652 bool oom_zonelist_trylock(struct zonelist *zonelist, gfp_t gfp_mask)
653 {
654         struct zoneref *z;
655         struct zone *zone;
656         bool ret = true;
657 
658         spin_lock(&zone_scan_lock);
659         for_each_zone_zonelist(zone, z, zonelist, gfp_zone(gfp_mask))
660                 if (test_bit(ZONE_OOM_LOCKED, &zone->flags)) {
661                         ret = false;
662                         goto out;
663                 }
664 
665         /*
666          * Lock each zone in the zonelist under zone_scan_lock so a parallel
667          * call to oom_zonelist_trylock() doesn't succeed when it shouldn't.
668          */
669         for_each_zone_zonelist(zone, z, zonelist, gfp_zone(gfp_mask))
670                 set_bit(ZONE_OOM_LOCKED, &zone->flags);
671 
672 out:
673         spin_unlock(&zone_scan_lock);
674         return ret;
675 }
676 
677 /*
678  * Clears the ZONE_OOM_LOCKED flag for all zones in the zonelist so that failed
679  * allocation attempts with zonelists containing them may now recall the OOM
680  * killer, if necessary.
681  */
682 void oom_zonelist_unlock(struct zonelist *zonelist, gfp_t gfp_mask)
683 {
684         struct zoneref *z;
685         struct zone *zone;
686 
687         spin_lock(&zone_scan_lock);
688         for_each_zone_zonelist(zone, z, zonelist, gfp_zone(gfp_mask))
689                 clear_bit(ZONE_OOM_LOCKED, &zone->flags);
690         spin_unlock(&zone_scan_lock);
691 }
692 
693 /**
694  * __out_of_memory - kill the "best" process when we run out of memory
695  * @zonelist: zonelist pointer
696  * @gfp_mask: memory allocation flags
697  * @order: amount of memory being requested as a power of 2
698  * @nodemask: nodemask passed to page allocator
699  * @force_kill: true if a task must be killed, even if others are exiting
700  *
701  * If we run out of memory, we have the choice between either
702  * killing a random task (bad), letting the system crash (worse)
703  * OR try to be smart about which process to kill. Note that we
704  * don't have to be perfect here, we just have to be good.
705  */
706 static void __out_of_memory(struct zonelist *zonelist, gfp_t gfp_mask,
707                 int order, nodemask_t *nodemask, bool force_kill)
708 {
709         const nodemask_t *mpol_mask;
710         struct task_struct *p;
711         unsigned long totalpages;
712         unsigned long freed = 0;
713         unsigned int uninitialized_var(points);
714         enum oom_constraint constraint = CONSTRAINT_NONE;
715         int killed = 0;
716 
717         blocking_notifier_call_chain(&oom_notify_list, 0, &freed);
718         if (freed > 0)
719                 /* Got some memory back in the last second. */
720                 return;
721 
722         /*
723          * If current has a pending SIGKILL or is exiting, then automatically
724          * select it.  The goal is to allow it to allocate so that it may
725          * quickly exit and free its memory.
726          *
727          * But don't select if current has already released its mm and cleared
728          * TIF_MEMDIE flag at exit_mm(), otherwise an OOM livelock may occur.
729          */
730         if (current->mm &&
731             (fatal_signal_pending(current) || task_will_free_mem(current))) {
732                 mark_tsk_oom_victim(current);
733                 return;
734         }
735 
736         /*
737          * Check if there were limitations on the allocation (only relevant for
738          * NUMA) that may require different handling.
739          */
740         constraint = constrained_alloc(zonelist, gfp_mask, nodemask,
741                                                 &totalpages);
742         mpol_mask = (constraint == CONSTRAINT_MEMORY_POLICY) ? nodemask : NULL;
743         check_panic_on_oom(constraint, gfp_mask, order, mpol_mask);
744 
745         if (sysctl_oom_kill_allocating_task && current->mm &&
746             !oom_unkillable_task(current, NULL, nodemask) &&
747             current->signal->oom_score_adj != OOM_SCORE_ADJ_MIN) {
748                 get_task_struct(current);
749                 oom_kill_process(current, gfp_mask, order, 0, totalpages, NULL,
750                                  nodemask,
751                                  "Out of memory (oom_kill_allocating_task)");
752                 goto out;
753         }
754 
755         p = select_bad_process(&points, totalpages, mpol_mask, force_kill);
756         /* Found nothing?!?! Either we hang forever, or we panic. */
757         if (!p) {
758                 dump_header(NULL, gfp_mask, order, NULL, mpol_mask);
759                 panic("Out of memory and no killable processes...\n");
760         }
761         if (p != (void *)-1UL) {
762                 oom_kill_process(p, gfp_mask, order, points, totalpages, NULL,
763                                  nodemask, "Out of memory");
764                 killed = 1;
765         }
766 out:
767         /*
768          * Give the killed threads a good chance of exiting before trying to
769          * allocate memory again.
770          */
771         if (killed)
772                 schedule_timeout_killable(1);
773 }
774 
775 /**
776  * out_of_memory -  tries to invoke OOM killer.
777  * @zonelist: zonelist pointer
778  * @gfp_mask: memory allocation flags
779  * @order: amount of memory being requested as a power of 2
780  * @nodemask: nodemask passed to page allocator
781  * @force_kill: true if a task must be killed, even if others are exiting
782  *
783  * invokes __out_of_memory if the OOM is not disabled by oom_killer_disable()
784  * when it returns false. Otherwise returns true.
785  */
786 bool out_of_memory(struct zonelist *zonelist, gfp_t gfp_mask,
787                 int order, nodemask_t *nodemask, bool force_kill)
788 {
789         bool ret = false;
790 
791         down_read(&oom_sem);
792         if (!oom_killer_disabled) {
793                 __out_of_memory(zonelist, gfp_mask, order, nodemask, force_kill);
794                 ret = true;
795         }
796         up_read(&oom_sem);
797 
798         return ret;
799 }
800 
801 /*
802  * The pagefault handler calls here because it is out of memory, so kill a
803  * memory-hogging task.  If any populated zone has ZONE_OOM_LOCKED set, a
804  * parallel oom killing is already in progress so do nothing.
805  */
806 void pagefault_out_of_memory(void)
807 {
808         struct zonelist *zonelist;
809 
810         down_read(&oom_sem);
811         if (mem_cgroup_oom_synchronize(true))
812                 goto unlock;
813 
814         zonelist = node_zonelist(first_memory_node, GFP_KERNEL);
815         if (oom_zonelist_trylock(zonelist, GFP_KERNEL)) {
816                 if (!oom_killer_disabled)
817                         __out_of_memory(NULL, 0, 0, NULL, false);
818                 else
819                         /*
820                          * There shouldn't be any user tasks runable while the
821                          * OOM killer is disabled so the current task has to
822                          * be a racing OOM victim for which oom_killer_disable()
823                          * is waiting for.
824                          */
825                         WARN_ON(test_thread_flag(TIF_MEMDIE));
826 
827                 oom_zonelist_unlock(zonelist, GFP_KERNEL);
828         }
829 unlock:
830         up_read(&oom_sem);
831 }
832 

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