path: root/mm/oom_kill.c (plain)
blob: d514eebad905e21ce0c9793031b9584f1f8328bd

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	#include <linux/kthread.h>
39	#include <linux/init.h>
40	#include <linux/mmu_notifier.h>
41
42	#include <asm/tlb.h>
43	#include "internal.h"
44
45	#define CREATE_TRACE_POINTS
46	#include <trace/events/oom.h>
47
48	int sysctl_panic_on_oom;
49	int sysctl_oom_kill_allocating_task;
50	int sysctl_oom_dump_tasks = 1;
51
52	DEFINE_MUTEX(oom_lock);
53
54	#ifdef CONFIG_NUMA
55	/**
56	* has_intersects_mems_allowed() - check task eligiblity for kill
57	* @start: task struct of which task to consider
58	* @mask: nodemask passed to page allocator for mempolicy ooms
59	*
60	* Task eligibility is determined by whether or not a candidate task, @tsk,
61	* shares the same mempolicy nodes as current if it is bound by such a policy
62	* and whether or not it has the same set of allowed cpuset nodes.
63	*/
64	static bool has_intersects_mems_allowed(struct task_struct *start,
65	const nodemask_t *mask)
66	{
67	struct task_struct *tsk;
68	bool ret = false;
69
70	rcu_read_lock();
71	for_each_thread(start, tsk) {
72	if (mask) {
73	/*
74	* If this is a mempolicy constrained oom, tsk's
75	* cpuset is irrelevant. Only return true if its
76	* mempolicy intersects current, otherwise it may be
77	* needlessly killed.
78	*/
79	ret = mempolicy_nodemask_intersects(tsk, mask);
80	} else {
81	/*
82	* This is not a mempolicy constrained oom, so only
83	* check the mems of tsk's cpuset.
84	*/
85	ret = cpuset_mems_allowed_intersects(current, tsk);
86	}
87	if (ret)
88	break;
89	}
90	rcu_read_unlock();
91
92	return ret;
93	}
94	#else
95	static bool has_intersects_mems_allowed(struct task_struct *tsk,
96	const nodemask_t *mask)
97	{
98	return true;
99	}
100	#endif /* CONFIG_NUMA */
101
102	/*
103	* The process p may have detached its own ->mm while exiting or through
104	* use_mm(), but one or more of its subthreads may still have a valid
105	* pointer. Return p, or any of its subthreads with a valid ->mm, with
106	* task_lock() held.
107	*/
108	struct task_struct *find_lock_task_mm(struct task_struct *p)
109	{
110	struct task_struct *t;
111
112	rcu_read_lock();
113
114	for_each_thread(p, t) {
115	task_lock(t);
116	if (likely(t->mm))
117	goto found;
118	task_unlock(t);
119	}
120	t = NULL;
121	found:
122	rcu_read_unlock();
123
124	return t;
125	}
126
127	/*
128	* order == -1 means the oom kill is required by sysrq, otherwise only
129	* for display purposes.
130	*/
131	static inline bool is_sysrq_oom(struct oom_control *oc)
132	{
133	return oc->order == -1;
134	}
135
136	static inline bool is_memcg_oom(struct oom_control *oc)
137	{
138	return oc->memcg != NULL;
139	}
140
141	/* return true if the task is not adequate as candidate victim task. */
142	static bool oom_unkillable_task(struct task_struct *p,
143	struct mem_cgroup *memcg, const nodemask_t *nodemask)
144	{
145	if (is_global_init(p))
146	return true;
147	if (p->flags & PF_KTHREAD)
148	return true;
149
150	/* When mem_cgroup_out_of_memory() and p is not member of the group */
151	if (memcg && !task_in_mem_cgroup(p, memcg))
152	return true;
153
154	/* p may not have freeable memory in nodemask */
155	if (!has_intersects_mems_allowed(p, nodemask))
156	return true;
157
158	return false;
159	}
160
161	/**
162	* oom_badness - heuristic function to determine which candidate task to kill
163	* @p: task struct of which task we should calculate
164	* @totalpages: total present RAM allowed for page allocation
165	*
166	* The heuristic for determining which task to kill is made to be as simple and
167	* predictable as possible. The goal is to return the highest value for the
168	* task consuming the most memory to avoid subsequent oom failures.
169	*/
170	unsigned long oom_badness(struct task_struct *p, struct mem_cgroup *memcg,
171	const nodemask_t *nodemask, unsigned long totalpages)
172	{
173	long points;
174	long adj;
175
176	if (oom_unkillable_task(p, memcg, nodemask))
177	return 0;
178
179	p = find_lock_task_mm(p);
180	if (!p)
181	return 0;
182
183	/*
184	* Do not even consider tasks which are explicitly marked oom
185	* unkillable or have been already oom reaped or the are in
186	* the middle of vfork
187	*/
188	adj = (long)p->signal->oom_score_adj;
189	if (adj == OOM_SCORE_ADJ_MIN ||
190	test_bit(MMF_OOM_SKIP, &p->mm->flags) ||
191	in_vfork(p)) {
192	task_unlock(p);
193	return 0;
194	}
195
196	/*
197	* The baseline for the badness score is the proportion of RAM that each
198	* task's rss, pagetable and swap space use.
199	*/
200	points = get_mm_rss(p->mm) + get_mm_counter(p->mm, MM_SWAPENTS) +
201	atomic_long_read(&p->mm->nr_ptes) + mm_nr_pmds(p->mm);
202	task_unlock(p);
203
204	/*
205	* Root processes get 3% bonus, just like the __vm_enough_memory()
206	* implementation used by LSMs.
207	*/
208	if (has_capability_noaudit(p, CAP_SYS_ADMIN))
209	points -= (points * 3) / 100;
210
211	/* Normalize to oom_score_adj units */
212	adj *= totalpages / 1000;
213	points += adj;
214
215	/*
216	* Never return 0 for an eligible task regardless of the root bonus and
217	* oom_score_adj (oom_score_adj can't be OOM_SCORE_ADJ_MIN here).
218	*/
219	return points > 0 ? points : 1;
220	}
221
222	enum oom_constraint {
223	CONSTRAINT_NONE,
224	CONSTRAINT_CPUSET,
225	CONSTRAINT_MEMORY_POLICY,
226	CONSTRAINT_MEMCG,
227	};
228
229	/*
230	* Determine the type of allocation constraint.
231	*/
232	static enum oom_constraint constrained_alloc(struct oom_control *oc)
233	{
234	struct zone *zone;
235	struct zoneref *z;
236	enum zone_type high_zoneidx = gfp_zone(oc->gfp_mask);
237	bool cpuset_limited = false;
238	int nid;
239
240	if (is_memcg_oom(oc)) {
241	oc->totalpages = mem_cgroup_get_limit(oc->memcg) ?: 1;
242	return CONSTRAINT_MEMCG;
243	}
244
245	/* Default to all available memory */
246	oc->totalpages = totalram_pages + total_swap_pages;
247
248	if (!IS_ENABLED(CONFIG_NUMA))
249	return CONSTRAINT_NONE;
250
251	if (!oc->zonelist)
252	return CONSTRAINT_NONE;
253	/*
254	* Reach here only when __GFP_NOFAIL is used. So, we should avoid
255	* to kill current.We have to random task kill in this case.
256	* Hopefully, CONSTRAINT_THISNODE...but no way to handle it, now.
257	*/
258	if (oc->gfp_mask & __GFP_THISNODE)
259	return CONSTRAINT_NONE;
260
261	/*
262	* This is not a __GFP_THISNODE allocation, so a truncated nodemask in
263	* the page allocator means a mempolicy is in effect. Cpuset policy
264	* is enforced in get_page_from_freelist().
265	*/
266	if (oc->nodemask &&
267	!nodes_subset(node_states[N_MEMORY], *oc->nodemask)) {
268	oc->totalpages = total_swap_pages;
269	for_each_node_mask(nid, *oc->nodemask)
270	oc->totalpages += node_spanned_pages(nid);
271	return CONSTRAINT_MEMORY_POLICY;
272	}
273
274	/* Check this allocation failure is caused by cpuset's wall function */
275	for_each_zone_zonelist_nodemask(zone, z, oc->zonelist,
276	high_zoneidx, oc->nodemask)
277	if (!cpuset_zone_allowed(zone, oc->gfp_mask))
278	cpuset_limited = true;
279
280	if (cpuset_limited) {
281	oc->totalpages = total_swap_pages;
282	for_each_node_mask(nid, cpuset_current_mems_allowed)
283	oc->totalpages += node_spanned_pages(nid);
284	return CONSTRAINT_CPUSET;
285	}
286	return CONSTRAINT_NONE;
287	}
288
289	static int oom_evaluate_task(struct task_struct *task, void *arg)
290	{
291	struct oom_control *oc = arg;
292	unsigned long points;
293
294	if (oom_unkillable_task(task, NULL, oc->nodemask))
295	goto next;
296
297	/*
298	* This task already has access to memory reserves and is being killed.
299	* Don't allow any other task to have access to the reserves unless
300	* the task has MMF_OOM_SKIP because chances that it would release
301	* any memory is quite low.
302	*/
303	if (!is_sysrq_oom(oc) && tsk_is_oom_victim(task)) {
304	if (test_bit(MMF_OOM_SKIP, &task->signal->oom_mm->flags))
305	goto next;
306	goto abort;
307	}
308
309	/*
310	* If task is allocating a lot of memory and has been marked to be
311	* killed first if it triggers an oom, then select it.
312	*/
313	if (oom_task_origin(task)) {
314	points = ULONG_MAX;
315	goto select;
316	}
317
318	points = oom_badness(task, NULL, oc->nodemask, oc->totalpages);
319	if (!points || points < oc->chosen_points)
320	goto next;
321
322	/* Prefer thread group leaders for display purposes */
323	if (points == oc->chosen_points && thread_group_leader(oc->chosen))
324	goto next;
325	select:
326	if (oc->chosen)
327	put_task_struct(oc->chosen);
328	get_task_struct(task);
329	oc->chosen = task;
330	oc->chosen_points = points;
331	next:
332	return 0;
333	abort:
334	if (oc->chosen)
335	put_task_struct(oc->chosen);
336	oc->chosen = (void *)-1UL;
337	return 1;
338	}
339
340	/*
341	* Simple selection loop. We choose the process with the highest number of
342	* 'points'. In case scan was aborted, oc->chosen is set to -1.
343	*/
344	static void select_bad_process(struct oom_control *oc)
345	{
346	if (is_memcg_oom(oc))
347	mem_cgroup_scan_tasks(oc->memcg, oom_evaluate_task, oc);
348	else {
349	struct task_struct *p;
350
351	rcu_read_lock();
352	for_each_process(p)
353	if (oom_evaluate_task(p, oc))
354	break;
355	rcu_read_unlock();
356	}
357
358	oc->chosen_points = oc->chosen_points * 1000 / oc->totalpages;
359	}
360
361	/**
362	* dump_tasks - dump current memory state of all system tasks
363	* @memcg: current's memory controller, if constrained
364	* @nodemask: nodemask passed to page allocator for mempolicy ooms
365	*
366	* Dumps the current memory state of all eligible tasks. Tasks not in the same
367	* memcg, not in the same cpuset, or bound to a disjoint set of mempolicy nodes
368	* are not shown.
369	* State information includes task's pid, uid, tgid, vm size, rss, nr_ptes,
370	* swapents, oom_score_adj value, and name.
371	*/
372	static void dump_tasks(struct mem_cgroup *memcg, const nodemask_t *nodemask)
373	{
374	struct task_struct *p;
375	struct task_struct *task;
376
377	pr_info("[ pid ] uid tgid total_vm rss nr_ptes nr_pmds swapents oom_score_adj name\n");
378	rcu_read_lock();
379	for_each_process(p) {
380	if (oom_unkillable_task(p, memcg, nodemask))
381	continue;
382
383	task = find_lock_task_mm(p);
384	if (!task) {
385	/*
386	* This is a kthread or all of p's threads have already
387	* detached their mm's. There's no need to report
388	* them; they can't be oom killed anyway.
389	*/
390	continue;
391	}
392
393	pr_info("[%5d] %5d %5d %8lu %8lu %7ld %7ld %8lu %5hd %s\n",
394	task->pid, from_kuid(&init_user_ns, task_uid(task)),
395	task->tgid, task->mm->total_vm, get_mm_rss(task->mm),
396	atomic_long_read(&task->mm->nr_ptes),
397	mm_nr_pmds(task->mm),
398	get_mm_counter(task->mm, MM_SWAPENTS),
399	task->signal->oom_score_adj, task->comm);
400	task_unlock(task);
401	}
402	rcu_read_unlock();
403	}
404
405	static void dump_header(struct oom_control *oc, struct task_struct *p)
406	{
407	nodemask_t *nm = (oc->nodemask) ? oc->nodemask : &cpuset_current_mems_allowed;
408
409	pr_warn("%s invoked oom-killer: gfp_mask=%#x(%pGg), nodemask=%*pbl, order=%d, oom_score_adj=%hd\n",
410	current->comm, oc->gfp_mask, &oc->gfp_mask,
411	nodemask_pr_args(nm), oc->order,
412	current->signal->oom_score_adj);
413	if (!IS_ENABLED(CONFIG_COMPACTION) && oc->order)
414	pr_warn("COMPACTION is disabled!!!\n");
415
416	cpuset_print_current_mems_allowed();
417	dump_stack();
418	if (oc->memcg)
419	mem_cgroup_print_oom_info(oc->memcg, p);
420	else
421	show_mem(SHOW_MEM_FILTER_NODES);
422	if (sysctl_oom_dump_tasks)
423	dump_tasks(oc->memcg, oc->nodemask);
424	}
425
426	/*
427	* Number of OOM victims in flight
428	*/
429	static atomic_t oom_victims = ATOMIC_INIT(0);
430	static DECLARE_WAIT_QUEUE_HEAD(oom_victims_wait);
431
432	static bool oom_killer_disabled __read_mostly;
433
434	#define K(x) ((x) << (PAGE_SHIFT-10))
435
436	/*
437	* task->mm can be NULL if the task is the exited group leader. So to
438	* determine whether the task is using a particular mm, we examine all the
439	* task's threads: if one of those is using this mm then this task was also
440	* using it.
441	*/
442	bool process_shares_mm(struct task_struct *p, struct mm_struct *mm)
443	{
444	struct task_struct *t;
445
446	for_each_thread(p, t) {
447	struct mm_struct *t_mm = READ_ONCE(t->mm);
448	if (t_mm)
449	return t_mm == mm;
450	}
451	return false;
452	}
453
454
455	#ifdef CONFIG_MMU
456	/*
457	* OOM Reaper kernel thread which tries to reap the memory used by the OOM
458	* victim (if that is possible) to help the OOM killer to move on.
459	*/
460	static struct task_struct *oom_reaper_th;
461	static DECLARE_WAIT_QUEUE_HEAD(oom_reaper_wait);
462	static struct task_struct *oom_reaper_list;
463	static DEFINE_SPINLOCK(oom_reaper_lock);
464
465	static bool __oom_reap_task_mm(struct task_struct *tsk, struct mm_struct *mm)
466	{
467	struct mmu_gather tlb;
468	struct vm_area_struct *vma;
469	struct zap_details details = {.check_swap_entries = true,
470	.ignore_dirty = true};
471	bool ret = true;
472
473	/*
474	* We have to make sure to not race with the victim exit path
475	* and cause premature new oom victim selection:
476	* __oom_reap_task_mm exit_mm
477	* mmget_not_zero
478	* mmput
479	* atomic_dec_and_test
480	* exit_oom_victim
481	* [...]
482	* out_of_memory
483	* select_bad_process
484	* # no TIF_MEMDIE task selects new victim
485	* unmap_page_range # frees some memory
486	*/
487	mutex_lock(&oom_lock);
488
489	if (!down_read_trylock(&mm->mmap_sem)) {
490	ret = false;
491	goto unlock_oom;
492	}
493
494	/*
495	* If the mm has notifiers then we would need to invalidate them around
496	* unmap_page_range and that is risky because notifiers can sleep and
497	* what they do is basically undeterministic. So let's have a short
498	* sleep to give the oom victim some more time.
499	* TODO: we really want to get rid of this ugly hack and make sure that
500	* notifiers cannot block for unbounded amount of time and add
501	* mmu_notifier_invalidate_range_{start,end} around unmap_page_range
502	*/
503	if (mm_has_notifiers(mm)) {
504	up_read(&mm->mmap_sem);
505	schedule_timeout_idle(HZ);
506	goto unlock_oom;
507	}
508
509	/*
510	* increase mm_users only after we know we will reap something so
511	* that the mmput_async is called only when we have reaped something
512	* and delayed __mmput doesn't matter that much
513	*/
514	if (!mmget_not_zero(mm)) {
515	up_read(&mm->mmap_sem);
516	goto unlock_oom;
517	}
518
519	/*
520	* Tell all users of get_user/copy_from_user etc... that the content
521	* is no longer stable. No barriers really needed because unmapping
522	* should imply barriers already and the reader would hit a page fault
523	* if it stumbled over a reaped memory.
524	*/
525	set_bit(MMF_UNSTABLE, &mm->flags);
526
527	for (vma = mm->mmap ; vma; vma = vma->vm_next) {
528	if (is_vm_hugetlb_page(vma))
529	continue;
530
531	/*
532	* mlocked VMAs require explicit munlocking before unmap.
533	* Let's keep it simple here and skip such VMAs.
534	*/
535	if (vma->vm_flags & VM_LOCKED)
536	continue;
537
538	/*
539	* Only anonymous pages have a good chance to be dropped
540	* without additional steps which we cannot afford as we
541	* are OOM already.
542	*
543	* We do not even care about fs backed pages because all
544	* which are reclaimable have already been reclaimed and
545	* we do not want to block exit_mmap by keeping mm ref
546	* count elevated without a good reason.
547	*/
548	if (vma_is_anonymous(vma) || !(vma->vm_flags & VM_SHARED)) {
549	tlb_gather_mmu(&tlb, mm, vma->vm_start, vma->vm_end);
550	unmap_page_range(&tlb, vma, vma->vm_start, vma->vm_end,
551	&details);
552	tlb_finish_mmu(&tlb, vma->vm_start, vma->vm_end);
553	}
554	}
555	pr_info("oom_reaper: reaped process %d (%s), now anon-rss:%lukB, file-rss:%lukB, shmem-rss:%lukB\n",
556	task_pid_nr(tsk), tsk->comm,
557	K(get_mm_counter(mm, MM_ANONPAGES)),
558	K(get_mm_counter(mm, MM_FILEPAGES)),
559	K(get_mm_counter(mm, MM_SHMEMPAGES)));
560	up_read(&mm->mmap_sem);
561
562	/*
563	* Drop our reference but make sure the mmput slow path is called from a
564	* different context because we shouldn't risk we get stuck there and
565	* put the oom_reaper out of the way.
566	*/
567	mmput_async(mm);
568	unlock_oom:
569	mutex_unlock(&oom_lock);
570	return ret;
571	}
572
573	#define MAX_OOM_REAP_RETRIES 10
574	static void oom_reap_task(struct task_struct *tsk)
575	{
576	int attempts = 0;
577	struct mm_struct *mm = tsk->signal->oom_mm;
578
579	/* Retry the down_read_trylock(mmap_sem) a few times */
580	while (attempts++ < MAX_OOM_REAP_RETRIES && !__oom_reap_task_mm(tsk, mm))
581	schedule_timeout_idle(HZ/10);
582
583	if (attempts <= MAX_OOM_REAP_RETRIES)
584	goto done;
585
586
587	pr_info("oom_reaper: unable to reap pid:%d (%s)\n",
588	task_pid_nr(tsk), tsk->comm);
589	debug_show_all_locks();
590
591	done:
592	tsk->oom_reaper_list = NULL;
593
594	/*
595	* Hide this mm from OOM killer because it has been either reaped or
596	* somebody can't call up_write(mmap_sem).
597	*/
598	set_bit(MMF_OOM_SKIP, &mm->flags);
599
600	/* Drop a reference taken by wake_oom_reaper */
601	put_task_struct(tsk);
602	}
603
604	static int oom_reaper(void *unused)
605	{
606	while (true) {
607	struct task_struct *tsk = NULL;
608
609	wait_event_freezable(oom_reaper_wait, oom_reaper_list != NULL);
610	spin_lock(&oom_reaper_lock);
611	if (oom_reaper_list != NULL) {
612	tsk = oom_reaper_list;
613	oom_reaper_list = tsk->oom_reaper_list;
614	}
615	spin_unlock(&oom_reaper_lock);
616
617	if (tsk)
618	oom_reap_task(tsk);
619	}
620
621	return 0;
622	}
623
624	static void wake_oom_reaper(struct task_struct *tsk)
625	{
626	if (!oom_reaper_th)
627	return;
628
629	/* mm is already queued? */
630	if (test_and_set_bit(MMF_OOM_REAP_QUEUED, &tsk->signal->oom_mm->flags))
631	return;
632
633	get_task_struct(tsk);
634
635	spin_lock(&oom_reaper_lock);
636	tsk->oom_reaper_list = oom_reaper_list;
637	oom_reaper_list = tsk;
638	spin_unlock(&oom_reaper_lock);
639	wake_up(&oom_reaper_wait);
640	}
641
642	static int __init oom_init(void)
643	{
644	oom_reaper_th = kthread_run(oom_reaper, NULL, "oom_reaper");
645	if (IS_ERR(oom_reaper_th)) {
646	pr_err("Unable to start OOM reaper %ld. Continuing regardless\n",
647	PTR_ERR(oom_reaper_th));
648	oom_reaper_th = NULL;
649	}
650	return 0;
651	}
652	subsys_initcall(oom_init)
653	#else
654	static inline void wake_oom_reaper(struct task_struct *tsk)
655	{
656	}
657	#endif /* CONFIG_MMU */
658
659	/**
660	* mark_oom_victim - mark the given task as OOM victim
661	* @tsk: task to mark
662	*
663	* Has to be called with oom_lock held and never after
664	* oom has been disabled already.
665	*
666	* tsk->mm has to be non NULL and caller has to guarantee it is stable (either
667	* under task_lock or operate on the current).
668	*/
669	static void mark_oom_victim(struct task_struct *tsk)
670	{
671	struct mm_struct *mm = tsk->mm;
672
673	WARN_ON(oom_killer_disabled);
674	/* OOM killer might race with memcg OOM */
675	if (test_and_set_tsk_thread_flag(tsk, TIF_MEMDIE))
676	return;
677
678	/* oom_mm is bound to the signal struct life time. */
679	if (!cmpxchg(&tsk->signal->oom_mm, NULL, mm))
680	atomic_inc(&tsk->signal->oom_mm->mm_count);
681
682	/*
683	* Make sure that the task is woken up from uninterruptible sleep
684	* if it is frozen because OOM killer wouldn't be able to free
685	* any memory and livelock. freezing_slow_path will tell the freezer
686	* that TIF_MEMDIE tasks should be ignored.
687	*/
688	__thaw_task(tsk);
689	atomic_inc(&oom_victims);
690	}
691
692	/**
693	* exit_oom_victim - note the exit of an OOM victim
694	*/
695	void exit_oom_victim(void)
696	{
697	clear_thread_flag(TIF_MEMDIE);
698
699	if (!atomic_dec_return(&oom_victims))
700	wake_up_all(&oom_victims_wait);
701	}
702
703	/**
704	* oom_killer_enable - enable OOM killer
705	*/
706	void oom_killer_enable(void)
707	{
708	oom_killer_disabled = false;
709	}
710
711	/**
712	* oom_killer_disable - disable OOM killer
713	* @timeout: maximum timeout to wait for oom victims in jiffies
714	*
715	* Forces all page allocations to fail rather than trigger OOM killer.
716	* Will block and wait until all OOM victims are killed or the given
717	* timeout expires.
718	*
719	* The function cannot be called when there are runnable user tasks because
720	* the userspace would see unexpected allocation failures as a result. Any
721	* new usage of this function should be consulted with MM people.
722	*
723	* Returns true if successful and false if the OOM killer cannot be
724	* disabled.
725	*/
726	bool oom_killer_disable(signed long timeout)
727	{
728	signed long ret;
729
730	/*
731	* Make sure to not race with an ongoing OOM killer. Check that the
732	* current is not killed (possibly due to sharing the victim's memory).
733	*/
734	if (mutex_lock_killable(&oom_lock))
735	return false;
736	oom_killer_disabled = true;
737	mutex_unlock(&oom_lock);
738
739	ret = wait_event_interruptible_timeout(oom_victims_wait,
740	!atomic_read(&oom_victims), timeout);
741	if (ret <= 0) {
742	oom_killer_enable();
743	return false;
744	}
745
746	return true;
747	}
748
749	static inline bool __task_will_free_mem(struct task_struct *task)
750	{
751	struct signal_struct *sig = task->signal;
752
753	/*
754	* A coredumping process may sleep for an extended period in exit_mm(),
755	* so the oom killer cannot assume that the process will promptly exit
756	* and release memory.
757	*/
758	if (sig->flags & SIGNAL_GROUP_COREDUMP)
759	return false;
760
761	if (sig->flags & SIGNAL_GROUP_EXIT)
762	return true;
763
764	if (thread_group_empty(task) && (task->flags & PF_EXITING))
765	return true;
766
767	return false;
768	}
769
770	/*
771	* Checks whether the given task is dying or exiting and likely to
772	* release its address space. This means that all threads and processes
773	* sharing the same mm have to be killed or exiting.
774	* Caller has to make sure that task->mm is stable (hold task_lock or
775	* it operates on the current).
776	*/
777	static bool task_will_free_mem(struct task_struct *task)
778	{
779	struct mm_struct *mm = task->mm;
780	struct task_struct *p;
781	bool ret = true;
782
783	/*
784	* Skip tasks without mm because it might have passed its exit_mm and
785	* exit_oom_victim. oom_reaper could have rescued that but do not rely
786	* on that for now. We can consider find_lock_task_mm in future.
787	*/
788	if (!mm)
789	return false;
790
791	if (!__task_will_free_mem(task))
792	return false;
793
794	/*
795	* This task has already been drained by the oom reaper so there are
796	* only small chances it will free some more
797	*/
798	if (test_bit(MMF_OOM_SKIP, &mm->flags))
799	return false;
800
801	if (atomic_read(&mm->mm_users) <= 1)
802	return true;
803
804	/*
805	* Make sure that all tasks which share the mm with the given tasks
806	* are dying as well to make sure that a) nobody pins its mm and
807	* b) the task is also reapable by the oom reaper.
808	*/
809	rcu_read_lock();
810	for_each_process(p) {
811	if (!process_shares_mm(p, mm))
812	continue;
813	if (same_thread_group(task, p))
814	continue;
815	ret = __task_will_free_mem(p);
816	if (!ret)
817	break;
818	}
819	rcu_read_unlock();
820
821	return ret;
822	}
823
824	static void oom_kill_process(struct oom_control *oc, const char *message)
825	{
826	struct task_struct *p = oc->chosen;
827	unsigned int points = oc->chosen_points;
828	struct task_struct *victim = p;
829	struct task_struct *child;
830	struct task_struct *t;
831	struct mm_struct *mm;
832	unsigned int victim_points = 0;
833	static DEFINE_RATELIMIT_STATE(oom_rs, DEFAULT_RATELIMIT_INTERVAL,
834	DEFAULT_RATELIMIT_BURST);
835	bool can_oom_reap = true;
836
837	/*
838	* If the task is already exiting, don't alarm the sysadmin or kill
839	* its children or threads, just set TIF_MEMDIE so it can die quickly
840	*/
841	task_lock(p);
842	if (task_will_free_mem(p)) {
843	mark_oom_victim(p);
844	wake_oom_reaper(p);
845	task_unlock(p);
846	put_task_struct(p);
847	return;
848	}
849	task_unlock(p);
850
851	if (__ratelimit(&oom_rs))
852	dump_header(oc, p);
853
854	pr_err("%s: Kill process %d (%s) score %u or sacrifice child\n",
855	message, task_pid_nr(p), p->comm, points);
856
857	/*
858	* If any of p's children has a different mm and is eligible for kill,
859	* the one with the highest oom_badness() score is sacrificed for its
860	* parent. This attempts to lose the minimal amount of work done while
861	* still freeing memory.
862	*/
863	read_lock(&tasklist_lock);
864
865	/*
866	* The task 'p' might have already exited before reaching here. The
867	* put_task_struct() will free task_struct 'p' while the loop still try
868	* to access the field of 'p', so, get an extra reference.
869	*/
870	get_task_struct(p);
871	for_each_thread(p, t) {
872	list_for_each_entry(child, &t->children, sibling) {
873	unsigned int child_points;
874
875	if (process_shares_mm(child, p->mm))
876	continue;
877	/*
878	* oom_badness() returns 0 if the thread is unkillable
879	*/
880	child_points = oom_badness(child,
881	oc->memcg, oc->nodemask, oc->totalpages);
882	if (child_points > victim_points) {
883	put_task_struct(victim);
884	victim = child;
885	victim_points = child_points;
886	get_task_struct(victim);
887	}
888	}
889	}
890	put_task_struct(p);
891	read_unlock(&tasklist_lock);
892
893	p = find_lock_task_mm(victim);
894	if (!p) {
895	put_task_struct(victim);
896	return;
897	} else if (victim != p) {
898	get_task_struct(p);
899	put_task_struct(victim);
900	victim = p;
901	}
902
903	/* Get a reference to safely compare mm after task_unlock(victim) */
904	mm = victim->mm;
905	atomic_inc(&mm->mm_count);
906	/*
907	* We should send SIGKILL before setting TIF_MEMDIE in order to prevent
908	* the OOM victim from depleting the memory reserves from the user
909	* space under its control.
910	*/
911	do_send_sig_info(SIGKILL, SEND_SIG_FORCED, victim, true);
912	mark_oom_victim(victim);
913	pr_err("Killed process %d (%s) total-vm:%lukB, anon-rss:%lukB, file-rss:%lukB, shmem-rss:%lukB\n",
914	task_pid_nr(victim), victim->comm, K(victim->mm->total_vm),
915	K(get_mm_counter(victim->mm, MM_ANONPAGES)),
916	K(get_mm_counter(victim->mm, MM_FILEPAGES)),
917	K(get_mm_counter(victim->mm, MM_SHMEMPAGES)));
918	task_unlock(victim);
919
920	/*
921	* Kill all user processes sharing victim->mm in other thread groups, if
922	* any. They don't get access to memory reserves, though, to avoid
923	* depletion of all memory. This prevents mm->mmap_sem livelock when an
924	* oom killed thread cannot exit because it requires the semaphore and
925	* its contended by another thread trying to allocate memory itself.
926	* That thread will now get access to memory reserves since it has a
927	* pending fatal signal.
928	*/
929	rcu_read_lock();
930	for_each_process(p) {
931	if (!process_shares_mm(p, mm))
932	continue;
933	if (same_thread_group(p, victim))
934	continue;
935	if (is_global_init(p)) {
936	can_oom_reap = false;
937	set_bit(MMF_OOM_SKIP, &mm->flags);
938	pr_info("oom killer %d (%s) has mm pinned by %d (%s)\n",
939	task_pid_nr(victim), victim->comm,
940	task_pid_nr(p), p->comm);
941	continue;
942	}
943	/*
944	* No use_mm() user needs to read from the userspace so we are
945	* ok to reap it.
946	*/
947	if (unlikely(p->flags & PF_KTHREAD))
948	continue;
949	do_send_sig_info(SIGKILL, SEND_SIG_FORCED, p, true);
950	}
951	rcu_read_unlock();
952
953	if (can_oom_reap)
954	wake_oom_reaper(victim);
955
956	mmdrop(mm);
957	put_task_struct(victim);
958	}
959	#undef K
960
961	/*
962	* Determines whether the kernel must panic because of the panic_on_oom sysctl.
963	*/
964	static void check_panic_on_oom(struct oom_control *oc,
965	enum oom_constraint constraint)
966	{
967	if (likely(!sysctl_panic_on_oom))
968	return;
969	if (sysctl_panic_on_oom != 2) {
970	/*
971	* panic_on_oom == 1 only affects CONSTRAINT_NONE, the kernel
972	* does not panic for cpuset, mempolicy, or memcg allocation
973	* failures.
974	*/
975	if (constraint != CONSTRAINT_NONE)
976	return;
977	}
978	/* Do not panic for oom kills triggered by sysrq */
979	if (is_sysrq_oom(oc))
980	return;
981	dump_header(oc, NULL);
982	panic("Out of memory: %s panic_on_oom is enabled\n",
983	sysctl_panic_on_oom == 2 ? "compulsory" : "system-wide");
984	}
985
986	static BLOCKING_NOTIFIER_HEAD(oom_notify_list);
987
988	int register_oom_notifier(struct notifier_block *nb)
989	{
990	return blocking_notifier_chain_register(&oom_notify_list, nb);
991	}
992	EXPORT_SYMBOL_GPL(register_oom_notifier);
993
994	int unregister_oom_notifier(struct notifier_block *nb)
995	{
996	return blocking_notifier_chain_unregister(&oom_notify_list, nb);
997	}
998	EXPORT_SYMBOL_GPL(unregister_oom_notifier);
999
1000	/**
1001	* out_of_memory - kill the "best" process when we run out of memory
1002	* @oc: pointer to struct oom_control
1003	*
1004	* If we run out of memory, we have the choice between either
1005	* killing a random task (bad), letting the system crash (worse)
1006	* OR try to be smart about which process to kill. Note that we
1007	* don't have to be perfect here, we just have to be good.
1008	*/
1009	bool out_of_memory(struct oom_control *oc)
1010	{
1011	unsigned long freed = 0;
1012	enum oom_constraint constraint = CONSTRAINT_NONE;
1013
1014	if (oom_killer_disabled)
1015	return false;
1016
1017	if (!is_memcg_oom(oc)) {
1018	blocking_notifier_call_chain(&oom_notify_list, 0, &freed);
1019	if (freed > 0)
1020	/* Got some memory back in the last second. */
1021	return true;
1022	}
1023
1024	/*
1025	* If current has a pending SIGKILL or is exiting, then automatically
1026	* select it. The goal is to allow it to allocate so that it may
1027	* quickly exit and free its memory.
1028	*/
1029	if (task_will_free_mem(current)) {
1030	mark_oom_victim(current);
1031	wake_oom_reaper(current);
1032	return true;
1033	}
1034
1035	/*
1036	* The OOM killer does not compensate for IO-less reclaim.
1037	* pagefault_out_of_memory lost its gfp context so we have to
1038	* make sure exclude 0 mask - all other users should have at least
1039	* ___GFP_DIRECT_RECLAIM to get here.
1040	*/
1041	if (oc->gfp_mask && !(oc->gfp_mask & (__GFP_FS|__GFP_NOFAIL)))
1042	return true;
1043
1044	/*
1045	* Check if there were limitations on the allocation (only relevant for
1046	* NUMA and memcg) that may require different handling.
1047	*/
1048	constraint = constrained_alloc(oc);
1049	if (constraint != CONSTRAINT_MEMORY_POLICY)
1050	oc->nodemask = NULL;
1051	check_panic_on_oom(oc, constraint);
1052
1053	if (!is_memcg_oom(oc) && sysctl_oom_kill_allocating_task &&
1054	current->mm && !oom_unkillable_task(current, NULL, oc->nodemask) &&
1055	current->signal->oom_score_adj != OOM_SCORE_ADJ_MIN) {
1056	get_task_struct(current);
1057	oc->chosen = current;
1058	oom_kill_process(oc, "Out of memory (oom_kill_allocating_task)");
1059	return true;
1060	}
1061
1062	select_bad_process(oc);
1063	/* Found nothing?!?! Either we hang forever, or we panic. */
1064	if (!oc->chosen && !is_sysrq_oom(oc) && !is_memcg_oom(oc)) {
1065	dump_header(oc, NULL);
1066	panic("Out of memory and no killable processes...\n");
1067	}
1068	if (oc->chosen && oc->chosen != (void *)-1UL) {
1069	oom_kill_process(oc, !is_memcg_oom(oc) ? "Out of memory" :
1070	"Memory cgroup out of memory");
1071	/*
1072	* Give the killed process a good chance to exit before trying
1073	* to allocate memory again.
1074	*/
1075	schedule_timeout_killable(1);
1076	}
1077	return !!oc->chosen;
1078	}
1079
1080	/*
1081	* The pagefault handler calls here because it is out of memory, so kill a
1082	* memory-hogging task. If oom_lock is held by somebody else, a parallel oom
1083	* killing is already in progress so do nothing.
1084	*/
1085	void pagefault_out_of_memory(void)
1086	{
1087	struct oom_control oc = {
1088	.zonelist = NULL,
1089	.nodemask = NULL,
1090	.memcg = NULL,
1091	.gfp_mask = 0,
1092	.order = 0,
1093	};
1094
1095	if (mem_cgroup_oom_synchronize(true))
1096	return;
1097
1098	if (!mutex_trylock(&oom_lock))
1099	return;
1100	out_of_memory(&oc);
1101	mutex_unlock(&oom_lock);
1102	}
1103