Root/mm/oom_kill.c

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/module.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
36int sysctl_panic_on_oom;
37int sysctl_oom_kill_allocating_task;
38int sysctl_oom_dump_tasks = 1;
39static DEFINE_SPINLOCK(zone_scan_lock);
40
41/**
42 * test_set_oom_score_adj() - set current's oom_score_adj and return old value
43 * @new_val: new oom_score_adj value
44 *
45 * Sets the oom_score_adj value for current to @new_val with proper
46 * synchronization and returns the old value. Usually used to temporarily
47 * set a value, save the old value in the caller, and then reinstate it later.
48 */
49int test_set_oom_score_adj(int new_val)
50{
51    struct sighand_struct *sighand = current->sighand;
52    int old_val;
53
54    spin_lock_irq(&sighand->siglock);
55    old_val = current->signal->oom_score_adj;
56    if (new_val != old_val) {
57        if (new_val == OOM_SCORE_ADJ_MIN)
58            atomic_inc(&current->mm->oom_disable_count);
59        else if (old_val == OOM_SCORE_ADJ_MIN)
60            atomic_dec(&current->mm->oom_disable_count);
61        current->signal->oom_score_adj = new_val;
62    }
63    spin_unlock_irq(&sighand->siglock);
64
65    return old_val;
66}
67
68#ifdef CONFIG_NUMA
69/**
70 * has_intersects_mems_allowed() - check task eligiblity for kill
71 * @tsk: task struct of which task to consider
72 * @mask: nodemask passed to page allocator for mempolicy ooms
73 *
74 * Task eligibility is determined by whether or not a candidate task, @tsk,
75 * shares the same mempolicy nodes as current if it is bound by such a policy
76 * and whether or not it has the same set of allowed cpuset nodes.
77 */
78static bool has_intersects_mems_allowed(struct task_struct *tsk,
79                    const nodemask_t *mask)
80{
81    struct task_struct *start = tsk;
82
83    do {
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            if (mempolicy_nodemask_intersects(tsk, mask))
92                return true;
93        } else {
94            /*
95             * This is not a mempolicy constrained oom, so only
96             * check the mems of tsk's cpuset.
97             */
98            if (cpuset_mems_allowed_intersects(current, tsk))
99                return true;
100        }
101    } while_each_thread(start, tsk);
102
103    return false;
104}
105#else
106static bool has_intersects_mems_allowed(struct task_struct *tsk,
107                    const nodemask_t *mask)
108{
109    return true;
110}
111#endif /* CONFIG_NUMA */
112
113/*
114 * The process p may have detached its own ->mm while exiting or through
115 * use_mm(), but one or more of its subthreads may still have a valid
116 * pointer. Return p, or any of its subthreads with a valid ->mm, with
117 * task_lock() held.
118 */
119struct task_struct *find_lock_task_mm(struct task_struct *p)
120{
121    struct task_struct *t = p;
122
123    do {
124        task_lock(t);
125        if (likely(t->mm))
126            return t;
127        task_unlock(t);
128    } while_each_thread(p, t);
129
130    return NULL;
131}
132
133/* return true if the task is not adequate as candidate victim task. */
134static bool oom_unkillable_task(struct task_struct *p,
135        const struct mem_cgroup *mem, const nodemask_t *nodemask)
136{
137    if (is_global_init(p))
138        return true;
139    if (p->flags & PF_KTHREAD)
140        return true;
141
142    /* When mem_cgroup_out_of_memory() and p is not member of the group */
143    if (mem && !task_in_mem_cgroup(p, mem))
144        return true;
145
146    /* p may not have freeable memory in nodemask */
147    if (!has_intersects_mems_allowed(p, nodemask))
148        return true;
149
150    return false;
151}
152
153/**
154 * oom_badness - heuristic function to determine which candidate task to kill
155 * @p: task struct of which task we should calculate
156 * @totalpages: total present RAM allowed for page allocation
157 *
158 * The heuristic for determining which task to kill is made to be as simple and
159 * predictable as possible. The goal is to return the highest value for the
160 * task consuming the most memory to avoid subsequent oom failures.
161 */
162unsigned int oom_badness(struct task_struct *p, struct mem_cgroup *mem,
163              const nodemask_t *nodemask, unsigned long totalpages)
164{
165    int points;
166
167    if (oom_unkillable_task(p, mem, nodemask))
168        return 0;
169
170    p = find_lock_task_mm(p);
171    if (!p)
172        return 0;
173
174    /*
175     * Shortcut check for a thread sharing p->mm that is OOM_SCORE_ADJ_MIN
176     * so the entire heuristic doesn't need to be executed for something
177     * that cannot be killed.
178     */
179    if (atomic_read(&p->mm->oom_disable_count)) {
180        task_unlock(p);
181        return 0;
182    }
183
184    /*
185     * The memory controller may have a limit of 0 bytes, so avoid a divide
186     * by zero, if necessary.
187     */
188    if (!totalpages)
189        totalpages = 1;
190
191    /*
192     * The baseline for the badness score is the proportion of RAM that each
193     * task's rss, pagetable and swap space use.
194     */
195    points = get_mm_rss(p->mm) + p->mm->nr_ptes;
196    points += get_mm_counter(p->mm, MM_SWAPENTS);
197
198    points *= 1000;
199    points /= totalpages;
200    task_unlock(p);
201
202    /*
203     * Root processes get 3% bonus, just like the __vm_enough_memory()
204     * implementation used by LSMs.
205     */
206    if (has_capability_noaudit(p, CAP_SYS_ADMIN))
207        points -= 30;
208
209    /*
210     * /proc/pid/oom_score_adj ranges from -1000 to +1000 such that it may
211     * either completely disable oom killing or always prefer a certain
212     * task.
213     */
214    points += p->signal->oom_score_adj;
215
216    /*
217     * Never return 0 for an eligible task that may be killed since it's
218     * possible that no single user task uses more than 0.1% of memory and
219     * no single admin tasks uses more than 3.0%.
220     */
221    if (points <= 0)
222        return 1;
223    return (points < 1000) ? points : 1000;
224}
225
226/*
227 * Determine the type of allocation constraint.
228 */
229#ifdef CONFIG_NUMA
230static enum oom_constraint constrained_alloc(struct zonelist *zonelist,
231                gfp_t gfp_mask, nodemask_t *nodemask,
232                unsigned long *totalpages)
233{
234    struct zone *zone;
235    struct zoneref *z;
236    enum zone_type high_zoneidx = gfp_zone(gfp_mask);
237    bool cpuset_limited = false;
238    int nid;
239
240    /* Default to all available memory */
241    *totalpages = totalram_pages + total_swap_pages;
242
243    if (!zonelist)
244        return CONSTRAINT_NONE;
245    /*
246     * Reach here only when __GFP_NOFAIL is used. So, we should avoid
247     * to kill current.We have to random task kill in this case.
248     * Hopefully, CONSTRAINT_THISNODE...but no way to handle it, now.
249     */
250    if (gfp_mask & __GFP_THISNODE)
251        return CONSTRAINT_NONE;
252
253    /*
254     * This is not a __GFP_THISNODE allocation, so a truncated nodemask in
255     * the page allocator means a mempolicy is in effect. Cpuset policy
256     * is enforced in get_page_from_freelist().
257     */
258    if (nodemask && !nodes_subset(node_states[N_HIGH_MEMORY], *nodemask)) {
259        *totalpages = total_swap_pages;
260        for_each_node_mask(nid, *nodemask)
261            *totalpages += node_spanned_pages(nid);
262        return CONSTRAINT_MEMORY_POLICY;
263    }
264
265    /* Check this allocation failure is caused by cpuset's wall function */
266    for_each_zone_zonelist_nodemask(zone, z, zonelist,
267            high_zoneidx, nodemask)
268        if (!cpuset_zone_allowed_softwall(zone, gfp_mask))
269            cpuset_limited = true;
270
271    if (cpuset_limited) {
272        *totalpages = total_swap_pages;
273        for_each_node_mask(nid, cpuset_current_mems_allowed)
274            *totalpages += node_spanned_pages(nid);
275        return CONSTRAINT_CPUSET;
276    }
277    return CONSTRAINT_NONE;
278}
279#else
280static enum oom_constraint constrained_alloc(struct zonelist *zonelist,
281                gfp_t gfp_mask, nodemask_t *nodemask,
282                unsigned long *totalpages)
283{
284    *totalpages = totalram_pages + total_swap_pages;
285    return CONSTRAINT_NONE;
286}
287#endif
288
289/*
290 * Simple selection loop. We chose the process with the highest
291 * number of 'points'. We expect the caller will lock the tasklist.
292 *
293 * (not docbooked, we don't want this one cluttering up the manual)
294 */
295static struct task_struct *select_bad_process(unsigned int *ppoints,
296        unsigned long totalpages, struct mem_cgroup *mem,
297        const nodemask_t *nodemask)
298{
299    struct task_struct *g, *p;
300    struct task_struct *chosen = NULL;
301    *ppoints = 0;
302
303    do_each_thread(g, p) {
304        unsigned int points;
305
306        if (!p->mm)
307            continue;
308        if (oom_unkillable_task(p, mem, nodemask))
309            continue;
310
311        /*
312         * This task already has access to memory reserves and is
313         * being killed. Don't allow any other task access to the
314         * memory reserve.
315         *
316         * Note: this may have a chance of deadlock if it gets
317         * blocked waiting for another task which itself is waiting
318         * for memory. Is there a better alternative?
319         */
320        if (test_tsk_thread_flag(p, TIF_MEMDIE))
321            return ERR_PTR(-1UL);
322
323        if (p->flags & PF_EXITING) {
324            /*
325             * If p is the current task and is in the process of
326             * releasing memory, we allow the "kill" to set
327             * TIF_MEMDIE, which will allow it to gain access to
328             * memory reserves. Otherwise, it may stall forever.
329             *
330             * The loop isn't broken here, however, in case other
331             * threads are found to have already been oom killed.
332             */
333            if (p == current) {
334                chosen = p;
335                *ppoints = 1000;
336            } else {
337                /*
338                 * If this task is not being ptraced on exit,
339                 * then wait for it to finish before killing
340                 * some other task unnecessarily.
341                 */
342                if (!(task_ptrace(p->group_leader) &
343                            PT_TRACE_EXIT))
344                    return ERR_PTR(-1UL);
345            }
346        }
347
348        points = oom_badness(p, mem, nodemask, totalpages);
349        if (points > *ppoints) {
350            chosen = p;
351            *ppoints = points;
352        }
353    } while_each_thread(g, p);
354
355    return chosen;
356}
357
358/**
359 * dump_tasks - dump current memory state of all system tasks
360 * @mem: current's memory controller, if constrained
361 * @nodemask: nodemask passed to page allocator for mempolicy ooms
362 *
363 * Dumps the current memory state of all eligible tasks. Tasks not in the same
364 * memcg, not in the same cpuset, or bound to a disjoint set of mempolicy nodes
365 * are not shown.
366 * State information includes task's pid, uid, tgid, vm size, rss, cpu, oom_adj
367 * value, oom_score_adj value, and name.
368 *
369 * Call with tasklist_lock read-locked.
370 */
371static void dump_tasks(const struct mem_cgroup *mem, const nodemask_t *nodemask)
372{
373    struct task_struct *p;
374    struct task_struct *task;
375
376    pr_info("[ pid ] uid tgid total_vm rss cpu oom_adj oom_score_adj name\n");
377    for_each_process(p) {
378        if (oom_unkillable_task(p, mem, nodemask))
379            continue;
380
381        task = find_lock_task_mm(p);
382        if (!task) {
383            /*
384             * This is a kthread or all of p's threads have already
385             * detached their mm's. There's no need to report
386             * them; they can't be oom killed anyway.
387             */
388            continue;
389        }
390
391        pr_info("[%5d] %5d %5d %8lu %8lu %3u %3d %5d %s\n",
392            task->pid, task_uid(task), task->tgid,
393            task->mm->total_vm, get_mm_rss(task->mm),
394            task_cpu(task), task->signal->oom_adj,
395            task->signal->oom_score_adj, task->comm);
396        task_unlock(task);
397    }
398}
399
400static void dump_header(struct task_struct *p, gfp_t gfp_mask, int order,
401            struct mem_cgroup *mem, const nodemask_t *nodemask)
402{
403    task_lock(current);
404    pr_warning("%s invoked oom-killer: gfp_mask=0x%x, order=%d, "
405        "oom_adj=%d, oom_score_adj=%d\n",
406        current->comm, gfp_mask, order, current->signal->oom_adj,
407        current->signal->oom_score_adj);
408    cpuset_print_task_mems_allowed(current);
409    task_unlock(current);
410    dump_stack();
411    mem_cgroup_print_oom_info(mem, p);
412    show_mem(SHOW_MEM_FILTER_NODES);
413    if (sysctl_oom_dump_tasks)
414        dump_tasks(mem, nodemask);
415}
416
417#define K(x) ((x) << (PAGE_SHIFT-10))
418static int oom_kill_task(struct task_struct *p, struct mem_cgroup *mem)
419{
420    struct task_struct *q;
421    struct mm_struct *mm;
422
423    p = find_lock_task_mm(p);
424    if (!p)
425        return 1;
426
427    /* mm cannot be safely dereferenced after task_unlock(p) */
428    mm = p->mm;
429
430    pr_err("Killed process %d (%s) total-vm:%lukB, anon-rss:%lukB, file-rss:%lukB\n",
431        task_pid_nr(p), p->comm, K(p->mm->total_vm),
432        K(get_mm_counter(p->mm, MM_ANONPAGES)),
433        K(get_mm_counter(p->mm, MM_FILEPAGES)));
434    task_unlock(p);
435
436    /*
437     * Kill all processes sharing p->mm in other thread groups, if any.
438     * They don't get access to memory reserves or a higher scheduler
439     * priority, though, to avoid depletion of all memory or task
440     * starvation. This prevents mm->mmap_sem livelock when an oom killed
441     * task cannot exit because it requires the semaphore and its contended
442     * by another thread trying to allocate memory itself. That thread will
443     * now get access to memory reserves since it has a pending fatal
444     * signal.
445     */
446    for_each_process(q)
447        if (q->mm == mm && !same_thread_group(q, p)) {
448            task_lock(q); /* Protect ->comm from prctl() */
449            pr_err("Kill process %d (%s) sharing same memory\n",
450                task_pid_nr(q), q->comm);
451            task_unlock(q);
452            force_sig(SIGKILL, q);
453        }
454
455    set_tsk_thread_flag(p, TIF_MEMDIE);
456    force_sig(SIGKILL, p);
457
458    return 0;
459}
460#undef K
461
462static int oom_kill_process(struct task_struct *p, gfp_t gfp_mask, int order,
463                unsigned int points, unsigned long totalpages,
464                struct mem_cgroup *mem, nodemask_t *nodemask,
465                const char *message)
466{
467    struct task_struct *victim = p;
468    struct task_struct *child;
469    struct task_struct *t = p;
470    unsigned int victim_points = 0;
471
472    if (printk_ratelimit())
473        dump_header(p, gfp_mask, order, mem, nodemask);
474
475    /*
476     * If the task is already exiting, don't alarm the sysadmin or kill
477     * its children or threads, just set TIF_MEMDIE so it can die quickly
478     */
479    if (p->flags & PF_EXITING) {
480        set_tsk_thread_flag(p, TIF_MEMDIE);
481        return 0;
482    }
483
484    task_lock(p);
485    pr_err("%s: Kill process %d (%s) score %d or sacrifice child\n",
486        message, task_pid_nr(p), p->comm, points);
487    task_unlock(p);
488
489    /*
490     * If any of p's children has a different mm and is eligible for kill,
491     * the one with the highest badness() score is sacrificed for its
492     * parent. This attempts to lose the minimal amount of work done while
493     * still freeing memory.
494     */
495    do {
496        list_for_each_entry(child, &t->children, sibling) {
497            unsigned int child_points;
498
499            if (child->mm == p->mm)
500                continue;
501            /*
502             * oom_badness() returns 0 if the thread is unkillable
503             */
504            child_points = oom_badness(child, mem, nodemask,
505                                totalpages);
506            if (child_points > victim_points) {
507                victim = child;
508                victim_points = child_points;
509            }
510        }
511    } while_each_thread(p, t);
512
513    return oom_kill_task(victim, mem);
514}
515
516/*
517 * Determines whether the kernel must panic because of the panic_on_oom sysctl.
518 */
519static void check_panic_on_oom(enum oom_constraint constraint, gfp_t gfp_mask,
520                int order, const nodemask_t *nodemask)
521{
522    if (likely(!sysctl_panic_on_oom))
523        return;
524    if (sysctl_panic_on_oom != 2) {
525        /*
526         * panic_on_oom == 1 only affects CONSTRAINT_NONE, the kernel
527         * does not panic for cpuset, mempolicy, or memcg allocation
528         * failures.
529         */
530        if (constraint != CONSTRAINT_NONE)
531            return;
532    }
533    read_lock(&tasklist_lock);
534    dump_header(NULL, gfp_mask, order, NULL, nodemask);
535    read_unlock(&tasklist_lock);
536    panic("Out of memory: %s panic_on_oom is enabled\n",
537        sysctl_panic_on_oom == 2 ? "compulsory" : "system-wide");
538}
539
540#ifdef CONFIG_CGROUP_MEM_RES_CTLR
541void mem_cgroup_out_of_memory(struct mem_cgroup *mem, gfp_t gfp_mask)
542{
543    unsigned long limit;
544    unsigned int points = 0;
545    struct task_struct *p;
546
547    /*
548     * If current has a pending SIGKILL, then automatically select it. The
549     * goal is to allow it to allocate so that it may quickly exit and free
550     * its memory.
551     */
552    if (fatal_signal_pending(current)) {
553        set_thread_flag(TIF_MEMDIE);
554        return;
555    }
556
557    check_panic_on_oom(CONSTRAINT_MEMCG, gfp_mask, 0, NULL);
558    limit = mem_cgroup_get_limit(mem) >> PAGE_SHIFT;
559    read_lock(&tasklist_lock);
560retry:
561    p = select_bad_process(&points, limit, mem, NULL);
562    if (!p || PTR_ERR(p) == -1UL)
563        goto out;
564
565    if (oom_kill_process(p, gfp_mask, 0, points, limit, mem, NULL,
566                "Memory cgroup out of memory"))
567        goto retry;
568out:
569    read_unlock(&tasklist_lock);
570}
571#endif
572
573static BLOCKING_NOTIFIER_HEAD(oom_notify_list);
574
575int register_oom_notifier(struct notifier_block *nb)
576{
577    return blocking_notifier_chain_register(&oom_notify_list, nb);
578}
579EXPORT_SYMBOL_GPL(register_oom_notifier);
580
581int unregister_oom_notifier(struct notifier_block *nb)
582{
583    return blocking_notifier_chain_unregister(&oom_notify_list, nb);
584}
585EXPORT_SYMBOL_GPL(unregister_oom_notifier);
586
587/*
588 * Try to acquire the OOM killer lock for the zones in zonelist. Returns zero
589 * if a parallel OOM killing is already taking place that includes a zone in
590 * the zonelist. Otherwise, locks all zones in the zonelist and returns 1.
591 */
592int try_set_zonelist_oom(struct zonelist *zonelist, gfp_t gfp_mask)
593{
594    struct zoneref *z;
595    struct zone *zone;
596    int ret = 1;
597
598    spin_lock(&zone_scan_lock);
599    for_each_zone_zonelist(zone, z, zonelist, gfp_zone(gfp_mask)) {
600        if (zone_is_oom_locked(zone)) {
601            ret = 0;
602            goto out;
603        }
604    }
605
606    for_each_zone_zonelist(zone, z, zonelist, gfp_zone(gfp_mask)) {
607        /*
608         * Lock each zone in the zonelist under zone_scan_lock so a
609         * parallel invocation of try_set_zonelist_oom() doesn't succeed
610         * when it shouldn't.
611         */
612        zone_set_flag(zone, ZONE_OOM_LOCKED);
613    }
614
615out:
616    spin_unlock(&zone_scan_lock);
617    return ret;
618}
619
620/*
621 * Clears the ZONE_OOM_LOCKED flag for all zones in the zonelist so that failed
622 * allocation attempts with zonelists containing them may now recall the OOM
623 * killer, if necessary.
624 */
625void clear_zonelist_oom(struct zonelist *zonelist, gfp_t gfp_mask)
626{
627    struct zoneref *z;
628    struct zone *zone;
629
630    spin_lock(&zone_scan_lock);
631    for_each_zone_zonelist(zone, z, zonelist, gfp_zone(gfp_mask)) {
632        zone_clear_flag(zone, ZONE_OOM_LOCKED);
633    }
634    spin_unlock(&zone_scan_lock);
635}
636
637/*
638 * Try to acquire the oom killer lock for all system zones. Returns zero if a
639 * parallel oom killing is taking place, otherwise locks all zones and returns
640 * non-zero.
641 */
642static int try_set_system_oom(void)
643{
644    struct zone *zone;
645    int ret = 1;
646
647    spin_lock(&zone_scan_lock);
648    for_each_populated_zone(zone)
649        if (zone_is_oom_locked(zone)) {
650            ret = 0;
651            goto out;
652        }
653    for_each_populated_zone(zone)
654        zone_set_flag(zone, ZONE_OOM_LOCKED);
655out:
656    spin_unlock(&zone_scan_lock);
657    return ret;
658}
659
660/*
661 * Clears ZONE_OOM_LOCKED for all system zones so that failed allocation
662 * attempts or page faults may now recall the oom killer, if necessary.
663 */
664static void clear_system_oom(void)
665{
666    struct zone *zone;
667
668    spin_lock(&zone_scan_lock);
669    for_each_populated_zone(zone)
670        zone_clear_flag(zone, ZONE_OOM_LOCKED);
671    spin_unlock(&zone_scan_lock);
672}
673
674/**
675 * out_of_memory - kill the "best" process when we run out of memory
676 * @zonelist: zonelist pointer
677 * @gfp_mask: memory allocation flags
678 * @order: amount of memory being requested as a power of 2
679 * @nodemask: nodemask passed to page allocator
680 *
681 * If we run out of memory, we have the choice between either
682 * killing a random task (bad), letting the system crash (worse)
683 * OR try to be smart about which process to kill. Note that we
684 * don't have to be perfect here, we just have to be good.
685 */
686void out_of_memory(struct zonelist *zonelist, gfp_t gfp_mask,
687        int order, nodemask_t *nodemask)
688{
689    const nodemask_t *mpol_mask;
690    struct task_struct *p;
691    unsigned long totalpages;
692    unsigned long freed = 0;
693    unsigned int points;
694    enum oom_constraint constraint = CONSTRAINT_NONE;
695    int killed = 0;
696
697    blocking_notifier_call_chain(&oom_notify_list, 0, &freed);
698    if (freed > 0)
699        /* Got some memory back in the last second. */
700        return;
701
702    /*
703     * If current has a pending SIGKILL, then automatically select it. The
704     * goal is to allow it to allocate so that it may quickly exit and free
705     * its memory.
706     */
707    if (fatal_signal_pending(current)) {
708        set_thread_flag(TIF_MEMDIE);
709        return;
710    }
711
712    /*
713     * Check if there were limitations on the allocation (only relevant for
714     * NUMA) that may require different handling.
715     */
716    constraint = constrained_alloc(zonelist, gfp_mask, nodemask,
717                        &totalpages);
718    mpol_mask = (constraint == CONSTRAINT_MEMORY_POLICY) ? nodemask : NULL;
719    check_panic_on_oom(constraint, gfp_mask, order, mpol_mask);
720
721    read_lock(&tasklist_lock);
722    if (sysctl_oom_kill_allocating_task &&
723        !oom_unkillable_task(current, NULL, nodemask) &&
724        current->mm && !atomic_read(&current->mm->oom_disable_count)) {
725        /*
726         * oom_kill_process() needs tasklist_lock held. If it returns
727         * non-zero, current could not be killed so we must fallback to
728         * the tasklist scan.
729         */
730        if (!oom_kill_process(current, gfp_mask, order, 0, totalpages,
731                NULL, nodemask,
732                "Out of memory (oom_kill_allocating_task)"))
733            goto out;
734    }
735
736retry:
737    p = select_bad_process(&points, totalpages, NULL, mpol_mask);
738    if (PTR_ERR(p) == -1UL)
739        goto out;
740
741    /* Found nothing?!?! Either we hang forever, or we panic. */
742    if (!p) {
743        dump_header(NULL, gfp_mask, order, NULL, mpol_mask);
744        read_unlock(&tasklist_lock);
745        panic("Out of memory and no killable processes...\n");
746    }
747
748    if (oom_kill_process(p, gfp_mask, order, points, totalpages, NULL,
749                nodemask, "Out of memory"))
750        goto retry;
751    killed = 1;
752out:
753    read_unlock(&tasklist_lock);
754
755    /*
756     * Give "p" a good chance of killing itself before we
757     * retry to allocate memory unless "p" is current
758     */
759    if (killed && !test_thread_flag(TIF_MEMDIE))
760        schedule_timeout_uninterruptible(1);
761}
762
763/*
764 * The pagefault handler calls here because it is out of memory, so kill a
765 * memory-hogging task. If a populated zone has ZONE_OOM_LOCKED set, a parallel
766 * oom killing is already in progress so do nothing. If a task is found with
767 * TIF_MEMDIE set, it has been killed so do nothing and allow it to exit.
768 */
769void pagefault_out_of_memory(void)
770{
771    if (try_set_system_oom()) {
772        out_of_memory(NULL, 0, 0, NULL);
773        clear_system_oom();
774    }
775    if (!test_thread_flag(TIF_MEMDIE))
776        schedule_timeout_uninterruptible(1);
777}
778

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