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/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
42int sysctl_panic_on_oom;
43int sysctl_oom_kill_allocating_task;
44int sysctl_oom_dump_tasks = 1;
45static DEFINE_SPINLOCK(zone_scan_lock);
46
47/*
48 * compare_swap_oom_score_adj() - compare and swap current's oom_score_adj
49 * @old_val: old oom_score_adj for compare
50 * @new_val: new oom_score_adj for swap
51 *
52 * Sets the oom_score_adj value for current to @new_val iff its present value is
53 * @old_val. Usually used to reinstate a previous value to prevent racing with
54 * userspacing tuning the value in the interim.
55 */
56void compare_swap_oom_score_adj(int old_val, int new_val)
57{
58    struct sighand_struct *sighand = current->sighand;
59
60    spin_lock_irq(&sighand->siglock);
61    if (current->signal->oom_score_adj == old_val)
62        current->signal->oom_score_adj = new_val;
63    trace_oom_score_adj_update(current);
64    spin_unlock_irq(&sighand->siglock);
65}
66
67/**
68 * test_set_oom_score_adj() - set current's oom_score_adj and return old value
69 * @new_val: new oom_score_adj value
70 *
71 * Sets the oom_score_adj value for current to @new_val with proper
72 * synchronization and returns the old value. Usually used to temporarily
73 * set a value, save the old value in the caller, and then reinstate it later.
74 */
75int test_set_oom_score_adj(int new_val)
76{
77    struct sighand_struct *sighand = current->sighand;
78    int old_val;
79
80    spin_lock_irq(&sighand->siglock);
81    old_val = current->signal->oom_score_adj;
82    current->signal->oom_score_adj = new_val;
83    trace_oom_score_adj_update(current);
84    spin_unlock_irq(&sighand->siglock);
85
86    return old_val;
87}
88
89#ifdef CONFIG_NUMA
90/**
91 * has_intersects_mems_allowed() - check task eligiblity for kill
92 * @tsk: task struct of which task to consider
93 * @mask: nodemask passed to page allocator for mempolicy ooms
94 *
95 * Task eligibility is determined by whether or not a candidate task, @tsk,
96 * shares the same mempolicy nodes as current if it is bound by such a policy
97 * and whether or not it has the same set of allowed cpuset nodes.
98 */
99static bool has_intersects_mems_allowed(struct task_struct *tsk,
100                    const nodemask_t *mask)
101{
102    struct task_struct *start = tsk;
103
104    do {
105        if (mask) {
106            /*
107             * If this is a mempolicy constrained oom, tsk's
108             * cpuset is irrelevant. Only return true if its
109             * mempolicy intersects current, otherwise it may be
110             * needlessly killed.
111             */
112            if (mempolicy_nodemask_intersects(tsk, mask))
113                return true;
114        } else {
115            /*
116             * This is not a mempolicy constrained oom, so only
117             * check the mems of tsk's cpuset.
118             */
119            if (cpuset_mems_allowed_intersects(current, tsk))
120                return true;
121        }
122    } while_each_thread(start, tsk);
123
124    return false;
125}
126#else
127static bool has_intersects_mems_allowed(struct task_struct *tsk,
128                    const nodemask_t *mask)
129{
130    return true;
131}
132#endif /* CONFIG_NUMA */
133
134/*
135 * The process p may have detached its own ->mm while exiting or through
136 * use_mm(), but one or more of its subthreads may still have a valid
137 * pointer. Return p, or any of its subthreads with a valid ->mm, with
138 * task_lock() held.
139 */
140struct task_struct *find_lock_task_mm(struct task_struct *p)
141{
142    struct task_struct *t = p;
143
144    do {
145        task_lock(t);
146        if (likely(t->mm))
147            return t;
148        task_unlock(t);
149    } while_each_thread(p, t);
150
151    return NULL;
152}
153
154/* return true if the task is not adequate as candidate victim task. */
155static bool oom_unkillable_task(struct task_struct *p,
156        const struct mem_cgroup *memcg, const nodemask_t *nodemask)
157{
158    if (is_global_init(p))
159        return true;
160    if (p->flags & PF_KTHREAD)
161        return true;
162
163    /* When mem_cgroup_out_of_memory() and p is not member of the group */
164    if (memcg && !task_in_mem_cgroup(p, memcg))
165        return true;
166
167    /* p may not have freeable memory in nodemask */
168    if (!has_intersects_mems_allowed(p, nodemask))
169        return true;
170
171    return false;
172}
173
174/**
175 * oom_badness - heuristic function to determine which candidate task to kill
176 * @p: task struct of which task we should calculate
177 * @totalpages: total present RAM allowed for page allocation
178 *
179 * The heuristic for determining which task to kill is made to be as simple and
180 * predictable as possible. The goal is to return the highest value for the
181 * task consuming the most memory to avoid subsequent oom failures.
182 */
183unsigned int oom_badness(struct task_struct *p, struct mem_cgroup *memcg,
184              const nodemask_t *nodemask, unsigned long totalpages)
185{
186    long points;
187
188    if (oom_unkillable_task(p, memcg, nodemask))
189        return 0;
190
191    p = find_lock_task_mm(p);
192    if (!p)
193        return 0;
194
195    if (p->signal->oom_score_adj == OOM_SCORE_ADJ_MIN) {
196        task_unlock(p);
197        return 0;
198    }
199
200    /*
201     * The memory controller may have a limit of 0 bytes, so avoid a divide
202     * by zero, if necessary.
203     */
204    if (!totalpages)
205        totalpages = 1;
206
207    /*
208     * The baseline for the badness score is the proportion of RAM that each
209     * task's rss, pagetable and swap space use.
210     */
211    points = get_mm_rss(p->mm) + p->mm->nr_ptes;
212    points += get_mm_counter(p->mm, MM_SWAPENTS);
213
214    points *= 1000;
215    points /= totalpages;
216    task_unlock(p);
217
218    /*
219     * Root processes get 3% bonus, just like the __vm_enough_memory()
220     * implementation used by LSMs.
221     */
222    if (has_capability_noaudit(p, CAP_SYS_ADMIN))
223        points -= 30;
224
225    /*
226     * /proc/pid/oom_score_adj ranges from -1000 to +1000 such that it may
227     * either completely disable oom killing or always prefer a certain
228     * task.
229     */
230    points += p->signal->oom_score_adj;
231
232    /*
233     * Never return 0 for an eligible task that may be killed since it's
234     * possible that no single user task uses more than 0.1% of memory and
235     * no single admin tasks uses more than 3.0%.
236     */
237    if (points <= 0)
238        return 1;
239    return (points < 1000) ? points : 1000;
240}
241
242/*
243 * Determine the type of allocation constraint.
244 */
245#ifdef CONFIG_NUMA
246static enum oom_constraint constrained_alloc(struct zonelist *zonelist,
247                gfp_t gfp_mask, nodemask_t *nodemask,
248                unsigned long *totalpages)
249{
250    struct zone *zone;
251    struct zoneref *z;
252    enum zone_type high_zoneidx = gfp_zone(gfp_mask);
253    bool cpuset_limited = false;
254    int nid;
255
256    /* Default to all available memory */
257    *totalpages = totalram_pages + total_swap_pages;
258
259    if (!zonelist)
260        return CONSTRAINT_NONE;
261    /*
262     * Reach here only when __GFP_NOFAIL is used. So, we should avoid
263     * to kill current.We have to random task kill in this case.
264     * Hopefully, CONSTRAINT_THISNODE...but no way to handle it, now.
265     */
266    if (gfp_mask & __GFP_THISNODE)
267        return CONSTRAINT_NONE;
268
269    /*
270     * This is not a __GFP_THISNODE allocation, so a truncated nodemask in
271     * the page allocator means a mempolicy is in effect. Cpuset policy
272     * is enforced in get_page_from_freelist().
273     */
274    if (nodemask && !nodes_subset(node_states[N_HIGH_MEMORY], *nodemask)) {
275        *totalpages = total_swap_pages;
276        for_each_node_mask(nid, *nodemask)
277            *totalpages += node_spanned_pages(nid);
278        return CONSTRAINT_MEMORY_POLICY;
279    }
280
281    /* Check this allocation failure is caused by cpuset's wall function */
282    for_each_zone_zonelist_nodemask(zone, z, zonelist,
283            high_zoneidx, nodemask)
284        if (!cpuset_zone_allowed_softwall(zone, gfp_mask))
285            cpuset_limited = true;
286
287    if (cpuset_limited) {
288        *totalpages = total_swap_pages;
289        for_each_node_mask(nid, cpuset_current_mems_allowed)
290            *totalpages += node_spanned_pages(nid);
291        return CONSTRAINT_CPUSET;
292    }
293    return CONSTRAINT_NONE;
294}
295#else
296static enum oom_constraint constrained_alloc(struct zonelist *zonelist,
297                gfp_t gfp_mask, nodemask_t *nodemask,
298                unsigned long *totalpages)
299{
300    *totalpages = totalram_pages + total_swap_pages;
301    return CONSTRAINT_NONE;
302}
303#endif
304
305/*
306 * Simple selection loop. We chose the process with the highest
307 * number of 'points'. We expect the caller will lock the tasklist.
308 *
309 * (not docbooked, we don't want this one cluttering up the manual)
310 */
311static struct task_struct *select_bad_process(unsigned int *ppoints,
312        unsigned long totalpages, struct mem_cgroup *memcg,
313        const nodemask_t *nodemask, bool force_kill)
314{
315    struct task_struct *g, *p;
316    struct task_struct *chosen = NULL;
317    *ppoints = 0;
318
319    do_each_thread(g, p) {
320        unsigned int points;
321
322        if (p->exit_state)
323            continue;
324        if (oom_unkillable_task(p, memcg, nodemask))
325            continue;
326
327        /*
328         * This task already has access to memory reserves and is
329         * being killed. Don't allow any other task access to the
330         * memory reserve.
331         *
332         * Note: this may have a chance of deadlock if it gets
333         * blocked waiting for another task which itself is waiting
334         * for memory. Is there a better alternative?
335         */
336        if (test_tsk_thread_flag(p, TIF_MEMDIE)) {
337            if (unlikely(frozen(p)))
338                __thaw_task(p);
339            if (!force_kill)
340                return ERR_PTR(-1UL);
341        }
342        if (!p->mm)
343            continue;
344
345        if (p->flags & PF_EXITING) {
346            /*
347             * If p is the current task and is in the process of
348             * releasing memory, we allow the "kill" to set
349             * TIF_MEMDIE, which will allow it to gain access to
350             * memory reserves. Otherwise, it may stall forever.
351             *
352             * The loop isn't broken here, however, in case other
353             * threads are found to have already been oom killed.
354             */
355            if (p == current) {
356                chosen = p;
357                *ppoints = 1000;
358            } else if (!force_kill) {
359                /*
360                 * If this task is not being ptraced on exit,
361                 * then wait for it to finish before killing
362                 * some other task unnecessarily.
363                 */
364                if (!(p->group_leader->ptrace & PT_TRACE_EXIT))
365                    return ERR_PTR(-1UL);
366            }
367        }
368
369        points = oom_badness(p, memcg, nodemask, totalpages);
370        if (points > *ppoints) {
371            chosen = p;
372            *ppoints = points;
373        }
374    } while_each_thread(g, p);
375
376    return chosen;
377}
378
379/**
380 * dump_tasks - dump current memory state of all system tasks
381 * @mem: current's memory controller, if constrained
382 * @nodemask: nodemask passed to page allocator for mempolicy ooms
383 *
384 * Dumps the current memory state of all eligible tasks. Tasks not in the same
385 * memcg, not in the same cpuset, or bound to a disjoint set of mempolicy nodes
386 * are not shown.
387 * State information includes task's pid, uid, tgid, vm size, rss, cpu, oom_adj
388 * value, oom_score_adj value, and name.
389 *
390 * Call with tasklist_lock read-locked.
391 */
392static void dump_tasks(const struct mem_cgroup *memcg, const nodemask_t *nodemask)
393{
394    struct task_struct *p;
395    struct task_struct *task;
396
397    pr_info("[ pid ] uid tgid total_vm rss cpu oom_adj oom_score_adj name\n");
398    for_each_process(p) {
399        if (oom_unkillable_task(p, memcg, nodemask))
400            continue;
401
402        task = find_lock_task_mm(p);
403        if (!task) {
404            /*
405             * This is a kthread or all of p's threads have already
406             * detached their mm's. There's no need to report
407             * them; they can't be oom killed anyway.
408             */
409            continue;
410        }
411
412        pr_info("[%5d] %5d %5d %8lu %8lu %3u %3d %5d %s\n",
413            task->pid, task_uid(task), task->tgid,
414            task->mm->total_vm, get_mm_rss(task->mm),
415            task_cpu(task), task->signal->oom_adj,
416            task->signal->oom_score_adj, task->comm);
417        task_unlock(task);
418    }
419}
420
421static void dump_header(struct task_struct *p, gfp_t gfp_mask, int order,
422            struct mem_cgroup *memcg, const nodemask_t *nodemask)
423{
424    task_lock(current);
425    pr_warning("%s invoked oom-killer: gfp_mask=0x%x, order=%d, "
426        "oom_adj=%d, oom_score_adj=%d\n",
427        current->comm, gfp_mask, order, current->signal->oom_adj,
428        current->signal->oom_score_adj);
429    cpuset_print_task_mems_allowed(current);
430    task_unlock(current);
431    dump_stack();
432    mem_cgroup_print_oom_info(memcg, p);
433    show_mem(SHOW_MEM_FILTER_NODES);
434    if (sysctl_oom_dump_tasks)
435        dump_tasks(memcg, nodemask);
436}
437
438#define K(x) ((x) << (PAGE_SHIFT-10))
439static void oom_kill_process(struct task_struct *p, gfp_t gfp_mask, int order,
440                 unsigned int points, unsigned long totalpages,
441                 struct mem_cgroup *memcg, nodemask_t *nodemask,
442                 const char *message)
443{
444    struct task_struct *victim = p;
445    struct task_struct *child;
446    struct task_struct *t = p;
447    struct mm_struct *mm;
448    unsigned int victim_points = 0;
449    static DEFINE_RATELIMIT_STATE(oom_rs, DEFAULT_RATELIMIT_INTERVAL,
450                          DEFAULT_RATELIMIT_BURST);
451
452    /*
453     * If the task is already exiting, don't alarm the sysadmin or kill
454     * its children or threads, just set TIF_MEMDIE so it can die quickly
455     */
456    if (p->flags & PF_EXITING) {
457        set_tsk_thread_flag(p, TIF_MEMDIE);
458        return;
459    }
460
461    if (__ratelimit(&oom_rs))
462        dump_header(p, gfp_mask, order, memcg, nodemask);
463
464    task_lock(p);
465    pr_err("%s: Kill process %d (%s) score %d or sacrifice child\n",
466        message, task_pid_nr(p), p->comm, points);
467    task_unlock(p);
468
469    /*
470     * If any of p's children has a different mm and is eligible for kill,
471     * the one with the highest oom_badness() score is sacrificed for its
472     * parent. This attempts to lose the minimal amount of work done while
473     * still freeing memory.
474     */
475    do {
476        list_for_each_entry(child, &t->children, sibling) {
477            unsigned int child_points;
478
479            if (child->mm == p->mm)
480                continue;
481            /*
482             * oom_badness() returns 0 if the thread is unkillable
483             */
484            child_points = oom_badness(child, memcg, nodemask,
485                                totalpages);
486            if (child_points > victim_points) {
487                victim = child;
488                victim_points = child_points;
489            }
490        }
491    } while_each_thread(p, t);
492
493    victim = find_lock_task_mm(victim);
494    if (!victim)
495        return;
496
497    /* mm cannot safely be dereferenced after task_unlock(victim) */
498    mm = victim->mm;
499    pr_err("Killed process %d (%s) total-vm:%lukB, anon-rss:%lukB, file-rss:%lukB\n",
500        task_pid_nr(victim), victim->comm, K(victim->mm->total_vm),
501        K(get_mm_counter(victim->mm, MM_ANONPAGES)),
502        K(get_mm_counter(victim->mm, MM_FILEPAGES)));
503    task_unlock(victim);
504
505    /*
506     * Kill all user processes sharing victim->mm in other thread groups, if
507     * any. They don't get access to memory reserves, though, to avoid
508     * depletion of all memory. This prevents mm->mmap_sem livelock when an
509     * oom killed thread cannot exit because it requires the semaphore and
510     * its contended by another thread trying to allocate memory itself.
511     * That thread will now get access to memory reserves since it has a
512     * pending fatal signal.
513     */
514    for_each_process(p)
515        if (p->mm == mm && !same_thread_group(p, victim) &&
516            !(p->flags & PF_KTHREAD)) {
517            if (p->signal->oom_score_adj == OOM_SCORE_ADJ_MIN)
518                continue;
519
520            task_lock(p); /* Protect ->comm from prctl() */
521            pr_err("Kill process %d (%s) sharing same memory\n",
522                task_pid_nr(p), p->comm);
523            task_unlock(p);
524            do_send_sig_info(SIGKILL, SEND_SIG_FORCED, p, true);
525        }
526
527    set_tsk_thread_flag(victim, TIF_MEMDIE);
528    do_send_sig_info(SIGKILL, SEND_SIG_FORCED, victim, true);
529}
530#undef K
531
532/*
533 * Determines whether the kernel must panic because of the panic_on_oom sysctl.
534 */
535static void check_panic_on_oom(enum oom_constraint constraint, gfp_t gfp_mask,
536                int order, const nodemask_t *nodemask)
537{
538    if (likely(!sysctl_panic_on_oom))
539        return;
540    if (sysctl_panic_on_oom != 2) {
541        /*
542         * panic_on_oom == 1 only affects CONSTRAINT_NONE, the kernel
543         * does not panic for cpuset, mempolicy, or memcg allocation
544         * failures.
545         */
546        if (constraint != CONSTRAINT_NONE)
547            return;
548    }
549    read_lock(&tasklist_lock);
550    dump_header(NULL, gfp_mask, order, NULL, nodemask);
551    read_unlock(&tasklist_lock);
552    panic("Out of memory: %s panic_on_oom is enabled\n",
553        sysctl_panic_on_oom == 2 ? "compulsory" : "system-wide");
554}
555
556#ifdef CONFIG_CGROUP_MEM_RES_CTLR
557void mem_cgroup_out_of_memory(struct mem_cgroup *memcg, gfp_t gfp_mask,
558                  int order)
559{
560    unsigned long limit;
561    unsigned int points = 0;
562    struct task_struct *p;
563
564    /*
565     * If current has a pending SIGKILL, then automatically select it. The
566     * goal is to allow it to allocate so that it may quickly exit and free
567     * its memory.
568     */
569    if (fatal_signal_pending(current)) {
570        set_thread_flag(TIF_MEMDIE);
571        return;
572    }
573
574    check_panic_on_oom(CONSTRAINT_MEMCG, gfp_mask, order, NULL);
575    limit = mem_cgroup_get_limit(memcg) >> PAGE_SHIFT;
576    read_lock(&tasklist_lock);
577    p = select_bad_process(&points, limit, memcg, NULL, false);
578    if (p && PTR_ERR(p) != -1UL)
579        oom_kill_process(p, gfp_mask, order, points, limit, memcg, NULL,
580                 "Memory cgroup out of memory");
581    read_unlock(&tasklist_lock);
582}
583#endif
584
585static BLOCKING_NOTIFIER_HEAD(oom_notify_list);
586
587int register_oom_notifier(struct notifier_block *nb)
588{
589    return blocking_notifier_chain_register(&oom_notify_list, nb);
590}
591EXPORT_SYMBOL_GPL(register_oom_notifier);
592
593int unregister_oom_notifier(struct notifier_block *nb)
594{
595    return blocking_notifier_chain_unregister(&oom_notify_list, nb);
596}
597EXPORT_SYMBOL_GPL(unregister_oom_notifier);
598
599/*
600 * Try to acquire the OOM killer lock for the zones in zonelist. Returns zero
601 * if a parallel OOM killing is already taking place that includes a zone in
602 * the zonelist. Otherwise, locks all zones in the zonelist and returns 1.
603 */
604int try_set_zonelist_oom(struct zonelist *zonelist, gfp_t gfp_mask)
605{
606    struct zoneref *z;
607    struct zone *zone;
608    int ret = 1;
609
610    spin_lock(&zone_scan_lock);
611    for_each_zone_zonelist(zone, z, zonelist, gfp_zone(gfp_mask)) {
612        if (zone_is_oom_locked(zone)) {
613            ret = 0;
614            goto out;
615        }
616    }
617
618    for_each_zone_zonelist(zone, z, zonelist, gfp_zone(gfp_mask)) {
619        /*
620         * Lock each zone in the zonelist under zone_scan_lock so a
621         * parallel invocation of try_set_zonelist_oom() doesn't succeed
622         * when it shouldn't.
623         */
624        zone_set_flag(zone, ZONE_OOM_LOCKED);
625    }
626
627out:
628    spin_unlock(&zone_scan_lock);
629    return ret;
630}
631
632/*
633 * Clears the ZONE_OOM_LOCKED flag for all zones in the zonelist so that failed
634 * allocation attempts with zonelists containing them may now recall the OOM
635 * killer, if necessary.
636 */
637void clear_zonelist_oom(struct zonelist *zonelist, gfp_t gfp_mask)
638{
639    struct zoneref *z;
640    struct zone *zone;
641
642    spin_lock(&zone_scan_lock);
643    for_each_zone_zonelist(zone, z, zonelist, gfp_zone(gfp_mask)) {
644        zone_clear_flag(zone, ZONE_OOM_LOCKED);
645    }
646    spin_unlock(&zone_scan_lock);
647}
648
649/*
650 * Try to acquire the oom killer lock for all system zones. Returns zero if a
651 * parallel oom killing is taking place, otherwise locks all zones and returns
652 * non-zero.
653 */
654static int try_set_system_oom(void)
655{
656    struct zone *zone;
657    int ret = 1;
658
659    spin_lock(&zone_scan_lock);
660    for_each_populated_zone(zone)
661        if (zone_is_oom_locked(zone)) {
662            ret = 0;
663            goto out;
664        }
665    for_each_populated_zone(zone)
666        zone_set_flag(zone, ZONE_OOM_LOCKED);
667out:
668    spin_unlock(&zone_scan_lock);
669    return ret;
670}
671
672/*
673 * Clears ZONE_OOM_LOCKED for all system zones so that failed allocation
674 * attempts or page faults may now recall the oom killer, if necessary.
675 */
676static void clear_system_oom(void)
677{
678    struct zone *zone;
679
680    spin_lock(&zone_scan_lock);
681    for_each_populated_zone(zone)
682        zone_clear_flag(zone, ZONE_OOM_LOCKED);
683    spin_unlock(&zone_scan_lock);
684}
685
686/**
687 * out_of_memory - kill the "best" process when we run out of memory
688 * @zonelist: zonelist pointer
689 * @gfp_mask: memory allocation flags
690 * @order: amount of memory being requested as a power of 2
691 * @nodemask: nodemask passed to page allocator
692 * @force_kill: true if a task must be killed, even if others are exiting
693 *
694 * If we run out of memory, we have the choice between either
695 * killing a random task (bad), letting the system crash (worse)
696 * OR try to be smart about which process to kill. Note that we
697 * don't have to be perfect here, we just have to be good.
698 */
699void out_of_memory(struct zonelist *zonelist, gfp_t gfp_mask,
700        int order, nodemask_t *nodemask, bool force_kill)
701{
702    const nodemask_t *mpol_mask;
703    struct task_struct *p;
704    unsigned long totalpages;
705    unsigned long freed = 0;
706    unsigned int points;
707    enum oom_constraint constraint = CONSTRAINT_NONE;
708    int killed = 0;
709
710    blocking_notifier_call_chain(&oom_notify_list, 0, &freed);
711    if (freed > 0)
712        /* Got some memory back in the last second. */
713        return;
714
715    /*
716     * If current has a pending SIGKILL, then automatically select it. The
717     * goal is to allow it to allocate so that it may quickly exit and free
718     * its memory.
719     */
720    if (fatal_signal_pending(current)) {
721        set_thread_flag(TIF_MEMDIE);
722        return;
723    }
724
725    /*
726     * Check if there were limitations on the allocation (only relevant for
727     * NUMA) that may require different handling.
728     */
729    constraint = constrained_alloc(zonelist, gfp_mask, nodemask,
730                        &totalpages);
731    mpol_mask = (constraint == CONSTRAINT_MEMORY_POLICY) ? nodemask : NULL;
732    check_panic_on_oom(constraint, gfp_mask, order, mpol_mask);
733
734    read_lock(&tasklist_lock);
735    if (sysctl_oom_kill_allocating_task &&
736        !oom_unkillable_task(current, NULL, nodemask) &&
737        current->mm) {
738        oom_kill_process(current, gfp_mask, order, 0, totalpages, NULL,
739                 nodemask,
740                 "Out of memory (oom_kill_allocating_task)");
741        goto out;
742    }
743
744    p = select_bad_process(&points, totalpages, NULL, mpol_mask,
745                   force_kill);
746    /* Found nothing?!?! Either we hang forever, or we panic. */
747    if (!p) {
748        dump_header(NULL, gfp_mask, order, NULL, mpol_mask);
749        read_unlock(&tasklist_lock);
750        panic("Out of memory and no killable processes...\n");
751    }
752    if (PTR_ERR(p) != -1UL) {
753        oom_kill_process(p, gfp_mask, order, points, totalpages, NULL,
754                 nodemask, "Out of memory");
755        killed = 1;
756    }
757out:
758    read_unlock(&tasklist_lock);
759
760    /*
761     * Give "p" a good chance of killing itself before we
762     * retry to allocate memory unless "p" is current
763     */
764    if (killed && !test_thread_flag(TIF_MEMDIE))
765        schedule_timeout_uninterruptible(1);
766}
767
768/*
769 * The pagefault handler calls here because it is out of memory, so kill a
770 * memory-hogging task. If a populated zone has ZONE_OOM_LOCKED set, a parallel
771 * oom killing is already in progress so do nothing. If a task is found with
772 * TIF_MEMDIE set, it has been killed so do nothing and allow it to exit.
773 */
774void pagefault_out_of_memory(void)
775{
776    if (try_set_system_oom()) {
777        out_of_memory(NULL, 0, 0, NULL, false);
778        clear_system_oom();
779    }
780    if (!test_thread_flag(TIF_MEMDIE))
781        schedule_timeout_uninterruptible(1);
782}
783

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