root/mm/oom_kill.c

DEFINITIONS

1. is_memcg_oom
2. oom_cpuset_eligible
3. oom_cpuset_eligible
4. find_lock_task_mm
5. is_sysrq_oom
6. oom_unkillable_task
7. is_dump_unreclaim_slabs
8. oom_badness
9. constrained_alloc
10. oom_evaluate_task
11. select_bad_process
12. dump_task
13. dump_tasks
14. dump_oom_summary
15. dump_header
16. process_shares_mm
17. __oom_reap_task_mm
18. oom_reap_task_mm
19. oom_reap_task
20. oom_reaper
21. wake_oom_reaper
22. oom_init
23. subsys_initcall
24. mark_oom_victim
25. exit_oom_victim
26. oom_killer_enable
27. oom_killer_disable
28. __task_will_free_mem
29. task_will_free_mem
30. __oom_kill_process
31. oom_kill_memcg_member
32. oom_kill_process
33. check_panic_on_oom
34. register_oom_notifier
35. unregister_oom_notifier
36. out_of_memory
37. pagefault_out_of_memory

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 /*
   3  *  linux/mm/oom_kill.c
   4  * 
   5  *  Copyright (C)  1998,2000  Rik van Riel
   6  *      Thanks go out to Claus Fischer for some serious inspiration and
   7  *      for goading me into coding this file...
   8  *  Copyright (C)  2010  Google, Inc.
   9  *      Rewritten by David Rientjes
  10  *
  11  *  The routines in this file are used to kill a process when
  12  *  we're seriously out of memory. This gets called from __alloc_pages()
  13  *  in mm/page_alloc.c when we really run out of memory.
  14  *
  15  *  Since we won't call these routines often (on a well-configured
  16  *  machine) this file will double as a 'coding guide' and a signpost
  17  *  for newbie kernel hackers. It features several pointers to major
  18  *  kernel subsystems and hints as to where to find out what things do.
  19  */
  20 
  21 #include <linux/oom.h>
  22 #include <linux/mm.h>
  23 #include <linux/err.h>
  24 #include <linux/gfp.h>
  25 #include <linux/sched.h>
  26 #include <linux/sched/mm.h>
  27 #include <linux/sched/coredump.h>
  28 #include <linux/sched/task.h>
  29 #include <linux/swap.h>
  30 #include <linux/timex.h>
  31 #include <linux/jiffies.h>
  32 #include <linux/cpuset.h>
  33 #include <linux/export.h>
  34 #include <linux/notifier.h>
  35 #include <linux/memcontrol.h>
  36 #include <linux/mempolicy.h>
  37 #include <linux/security.h>
  38 #include <linux/ptrace.h>
  39 #include <linux/freezer.h>
  40 #include <linux/ftrace.h>
  41 #include <linux/ratelimit.h>
  42 #include <linux/kthread.h>
  43 #include <linux/init.h>
  44 #include <linux/mmu_notifier.h>
  45 
  46 #include <asm/tlb.h>
  47 #include "internal.h"
  48 #include "slab.h"
  49 
  50 #define CREATE_TRACE_POINTS
  51 #include <trace/events/oom.h>
  52 
  53 int sysctl_panic_on_oom;
  54 int sysctl_oom_kill_allocating_task;
  55 int sysctl_oom_dump_tasks = 1;
  56 
  57 /*
  58  * Serializes oom killer invocations (out_of_memory()) from all contexts to
  59  * prevent from over eager oom killing (e.g. when the oom killer is invoked
  60  * from different domains).
  61  *
  62  * oom_killer_disable() relies on this lock to stabilize oom_killer_disabled
  63  * and mark_oom_victim
  64  */
  65 DEFINE_MUTEX(oom_lock);
  66 
  67 static inline bool is_memcg_oom(struct oom_control *oc)
  68 {
  69         return oc->memcg != NULL;
  70 }
  71 
  72 #ifdef CONFIG_NUMA
  73 /**
  74  * oom_cpuset_eligible() - check task eligiblity for kill
  75  * @start: task struct of which task to consider
  76  * @oc: pointer to struct oom_control
  77  *
  78  * Task eligibility is determined by whether or not a candidate task, @tsk,
  79  * shares the same mempolicy nodes as current if it is bound by such a policy
  80  * and whether or not it has the same set of allowed cpuset nodes.
  81  *
  82  * This function is assuming oom-killer context and 'current' has triggered
  83  * the oom-killer.
  84  */
  85 static bool oom_cpuset_eligible(struct task_struct *start,
  86                                 struct oom_control *oc)
  87 {
  88         struct task_struct *tsk;
  89         bool ret = false;
  90         const nodemask_t *mask = oc->nodemask;
  91 
  92         if (is_memcg_oom(oc))
  93                 return true;
  94 
  95         rcu_read_lock();
  96         for_each_thread(start, tsk) {
  97                 if (mask) {
  98                         /*
  99                          * If this is a mempolicy constrained oom, tsk's
 100                          * cpuset is irrelevant.  Only return true if its
 101                          * mempolicy intersects current, otherwise it may be
 102                          * needlessly killed.
 103                          */
 104                         ret = mempolicy_nodemask_intersects(tsk, mask);
 105                 } else {
 106                         /*
 107                          * This is not a mempolicy constrained oom, so only
 108                          * check the mems of tsk's cpuset.
 109                          */
 110                         ret = cpuset_mems_allowed_intersects(current, tsk);
 111                 }
 112                 if (ret)
 113                         break;
 114         }
 115         rcu_read_unlock();
 116 
 117         return ret;
 118 }
 119 #else
 120 static bool oom_cpuset_eligible(struct task_struct *tsk, struct oom_control *oc)
 121 {
 122         return true;
 123 }
 124 #endif /* CONFIG_NUMA */
 125 
 126 /*
 127  * The process p may have detached its own ->mm while exiting or through
 128  * use_mm(), but one or more of its subthreads may still have a valid
 129  * pointer.  Return p, or any of its subthreads with a valid ->mm, with
 130  * task_lock() held.
 131  */
 132 struct task_struct *find_lock_task_mm(struct task_struct *p)
 133 {
 134         struct task_struct *t;
 135 
 136         rcu_read_lock();
 137 
 138         for_each_thread(p, t) {
 139                 task_lock(t);
 140                 if (likely(t->mm))
 141                         goto found;
 142                 task_unlock(t);
 143         }
 144         t = NULL;
 145 found:
 146         rcu_read_unlock();
 147 
 148         return t;
 149 }
 150 
 151 /*
 152  * order == -1 means the oom kill is required by sysrq, otherwise only
 153  * for display purposes.
 154  */
 155 static inline bool is_sysrq_oom(struct oom_control *oc)
 156 {
 157         return oc->order == -1;
 158 }
 159 
 160 /* return true if the task is not adequate as candidate victim task. */
 161 static bool oom_unkillable_task(struct task_struct *p)
 162 {
 163         if (is_global_init(p))
 164                 return true;
 165         if (p->flags & PF_KTHREAD)
 166                 return true;
 167         return false;
 168 }
 169 
 170 /*
 171  * Print out unreclaimble slabs info when unreclaimable slabs amount is greater
 172  * than all user memory (LRU pages)
 173  */
 174 static bool is_dump_unreclaim_slabs(void)
 175 {
 176         unsigned long nr_lru;
 177 
 178         nr_lru = global_node_page_state(NR_ACTIVE_ANON) +
 179                  global_node_page_state(NR_INACTIVE_ANON) +
 180                  global_node_page_state(NR_ACTIVE_FILE) +
 181                  global_node_page_state(NR_INACTIVE_FILE) +
 182                  global_node_page_state(NR_ISOLATED_ANON) +
 183                  global_node_page_state(NR_ISOLATED_FILE) +
 184                  global_node_page_state(NR_UNEVICTABLE);
 185 
 186         return (global_node_page_state(NR_SLAB_UNRECLAIMABLE) > nr_lru);
 187 }
 188 
 189 /**
 190  * oom_badness - heuristic function to determine which candidate task to kill
 191  * @p: task struct of which task we should calculate
 192  * @totalpages: total present RAM allowed for page allocation
 193  *
 194  * The heuristic for determining which task to kill is made to be as simple and
 195  * predictable as possible.  The goal is to return the highest value for the
 196  * task consuming the most memory to avoid subsequent oom failures.
 197  */
 198 unsigned long oom_badness(struct task_struct *p, unsigned long totalpages)
 199 {
 200         long points;
 201         long adj;
 202 
 203         if (oom_unkillable_task(p))
 204                 return 0;
 205 
 206         p = find_lock_task_mm(p);
 207         if (!p)
 208                 return 0;
 209 
 210         /*
 211          * Do not even consider tasks which are explicitly marked oom
 212          * unkillable or have been already oom reaped or the are in
 213          * the middle of vfork
 214          */
 215         adj = (long)p->signal->oom_score_adj;
 216         if (adj == OOM_SCORE_ADJ_MIN ||
 217                         test_bit(MMF_OOM_SKIP, &p->mm->flags) ||
 218                         in_vfork(p)) {
 219                 task_unlock(p);
 220                 return 0;
 221         }
 222 
 223         /*
 224          * The baseline for the badness score is the proportion of RAM that each
 225          * task's rss, pagetable and swap space use.
 226          */
 227         points = get_mm_rss(p->mm) + get_mm_counter(p->mm, MM_SWAPENTS) +
 228                 mm_pgtables_bytes(p->mm) / PAGE_SIZE;
 229         task_unlock(p);
 230 
 231         /* Normalize to oom_score_adj units */
 232         adj *= totalpages / 1000;
 233         points += adj;
 234 
 235         /*
 236          * Never return 0 for an eligible task regardless of the root bonus and
 237          * oom_score_adj (oom_score_adj can't be OOM_SCORE_ADJ_MIN here).
 238          */
 239         return points > 0 ? points : 1;
 240 }
 241 
 242 static const char * const oom_constraint_text[] = {
 243         [CONSTRAINT_NONE] = "CONSTRAINT_NONE",
 244         [CONSTRAINT_CPUSET] = "CONSTRAINT_CPUSET",
 245         [CONSTRAINT_MEMORY_POLICY] = "CONSTRAINT_MEMORY_POLICY",
 246         [CONSTRAINT_MEMCG] = "CONSTRAINT_MEMCG",
 247 };
 248 
 249 /*
 250  * Determine the type of allocation constraint.
 251  */
 252 static enum oom_constraint constrained_alloc(struct oom_control *oc)
 253 {
 254         struct zone *zone;
 255         struct zoneref *z;
 256         enum zone_type high_zoneidx = gfp_zone(oc->gfp_mask);
 257         bool cpuset_limited = false;
 258         int nid;
 259 
 260         if (is_memcg_oom(oc)) {
 261                 oc->totalpages = mem_cgroup_get_max(oc->memcg) ?: 1;
 262                 return CONSTRAINT_MEMCG;
 263         }
 264 
 265         /* Default to all available memory */
 266         oc->totalpages = totalram_pages() + total_swap_pages;
 267 
 268         if (!IS_ENABLED(CONFIG_NUMA))
 269                 return CONSTRAINT_NONE;
 270 
 271         if (!oc->zonelist)
 272                 return CONSTRAINT_NONE;
 273         /*
 274          * Reach here only when __GFP_NOFAIL is used. So, we should avoid
 275          * to kill current.We have to random task kill in this case.
 276          * Hopefully, CONSTRAINT_THISNODE...but no way to handle it, now.
 277          */
 278         if (oc->gfp_mask & __GFP_THISNODE)
 279                 return CONSTRAINT_NONE;
 280 
 281         /*
 282          * This is not a __GFP_THISNODE allocation, so a truncated nodemask in
 283          * the page allocator means a mempolicy is in effect.  Cpuset policy
 284          * is enforced in get_page_from_freelist().
 285          */
 286         if (oc->nodemask &&
 287             !nodes_subset(node_states[N_MEMORY], *oc->nodemask)) {
 288                 oc->totalpages = total_swap_pages;
 289                 for_each_node_mask(nid, *oc->nodemask)
 290                         oc->totalpages += node_present_pages(nid);
 291                 return CONSTRAINT_MEMORY_POLICY;
 292         }
 293 
 294         /* Check this allocation failure is caused by cpuset's wall function */
 295         for_each_zone_zonelist_nodemask(zone, z, oc->zonelist,
 296                         high_zoneidx, oc->nodemask)
 297                 if (!cpuset_zone_allowed(zone, oc->gfp_mask))
 298                         cpuset_limited = true;
 299 
 300         if (cpuset_limited) {
 301                 oc->totalpages = total_swap_pages;
 302                 for_each_node_mask(nid, cpuset_current_mems_allowed)
 303                         oc->totalpages += node_present_pages(nid);
 304                 return CONSTRAINT_CPUSET;
 305         }
 306         return CONSTRAINT_NONE;
 307 }
 308 
 309 static int oom_evaluate_task(struct task_struct *task, void *arg)
 310 {
 311         struct oom_control *oc = arg;
 312         unsigned long points;
 313 
 314         if (oom_unkillable_task(task))
 315                 goto next;
 316 
 317         /* p may not have freeable memory in nodemask */
 318         if (!is_memcg_oom(oc) && !oom_cpuset_eligible(task, oc))
 319                 goto next;
 320 
 321         /*
 322          * This task already has access to memory reserves and is being killed.
 323          * Don't allow any other task to have access to the reserves unless
 324          * the task has MMF_OOM_SKIP because chances that it would release
 325          * any memory is quite low.
 326          */
 327         if (!is_sysrq_oom(oc) && tsk_is_oom_victim(task)) {
 328                 if (test_bit(MMF_OOM_SKIP, &task->signal->oom_mm->flags))
 329                         goto next;
 330                 goto abort;
 331         }
 332 
 333         /*
 334          * If task is allocating a lot of memory and has been marked to be
 335          * killed first if it triggers an oom, then select it.
 336          */
 337         if (oom_task_origin(task)) {
 338                 points = ULONG_MAX;
 339                 goto select;
 340         }
 341 
 342         points = oom_badness(task, oc->totalpages);
 343         if (!points || points < oc->chosen_points)
 344                 goto next;
 345 
 346 select:
 347         if (oc->chosen)
 348                 put_task_struct(oc->chosen);
 349         get_task_struct(task);
 350         oc->chosen = task;
 351         oc->chosen_points = points;
 352 next:
 353         return 0;
 354 abort:
 355         if (oc->chosen)
 356                 put_task_struct(oc->chosen);
 357         oc->chosen = (void *)-1UL;
 358         return 1;
 359 }
 360 
 361 /*
 362  * Simple selection loop. We choose the process with the highest number of
 363  * 'points'. In case scan was aborted, oc->chosen is set to -1.
 364  */
 365 static void select_bad_process(struct oom_control *oc)
 366 {
 367         if (is_memcg_oom(oc))
 368                 mem_cgroup_scan_tasks(oc->memcg, oom_evaluate_task, oc);
 369         else {
 370                 struct task_struct *p;
 371 
 372                 rcu_read_lock();
 373                 for_each_process(p)
 374                         if (oom_evaluate_task(p, oc))
 375                                 break;
 376                 rcu_read_unlock();
 377         }
 378 }
 379 
 380 static int dump_task(struct task_struct *p, void *arg)
 381 {
 382         struct oom_control *oc = arg;
 383         struct task_struct *task;
 384 
 385         if (oom_unkillable_task(p))
 386                 return 0;
 387 
 388         /* p may not have freeable memory in nodemask */
 389         if (!is_memcg_oom(oc) && !oom_cpuset_eligible(p, oc))
 390                 return 0;
 391 
 392         task = find_lock_task_mm(p);
 393         if (!task) {
 394                 /*
 395                  * This is a kthread or all of p's threads have already
 396                  * detached their mm's.  There's no need to report
 397                  * them; they can't be oom killed anyway.
 398                  */
 399                 return 0;
 400         }
 401 
 402         pr_info("[%7d] %5d %5d %8lu %8lu %8ld %8lu         %5hd %s\n",
 403                 task->pid, from_kuid(&init_user_ns, task_uid(task)),
 404                 task->tgid, task->mm->total_vm, get_mm_rss(task->mm),
 405                 mm_pgtables_bytes(task->mm),
 406                 get_mm_counter(task->mm, MM_SWAPENTS),
 407                 task->signal->oom_score_adj, task->comm);
 408         task_unlock(task);
 409 
 410         return 0;
 411 }
 412 
 413 /**
 414  * dump_tasks - dump current memory state of all system tasks
 415  * @oc: pointer to struct oom_control
 416  *
 417  * Dumps the current memory state of all eligible tasks.  Tasks not in the same
 418  * memcg, not in the same cpuset, or bound to a disjoint set of mempolicy nodes
 419  * are not shown.
 420  * State information includes task's pid, uid, tgid, vm size, rss,
 421  * pgtables_bytes, swapents, oom_score_adj value, and name.
 422  */
 423 static void dump_tasks(struct oom_control *oc)
 424 {
 425         pr_info("Tasks state (memory values in pages):\n");
 426         pr_info("[  pid  ]   uid  tgid total_vm      rss pgtables_bytes swapents oom_score_adj name\n");
 427 
 428         if (is_memcg_oom(oc))
 429                 mem_cgroup_scan_tasks(oc->memcg, dump_task, oc);
 430         else {
 431                 struct task_struct *p;
 432 
 433                 rcu_read_lock();
 434                 for_each_process(p)
 435                         dump_task(p, oc);
 436                 rcu_read_unlock();
 437         }
 438 }
 439 
 440 static void dump_oom_summary(struct oom_control *oc, struct task_struct *victim)
 441 {
 442         /* one line summary of the oom killer context. */
 443         pr_info("oom-kill:constraint=%s,nodemask=%*pbl",
 444                         oom_constraint_text[oc->constraint],
 445                         nodemask_pr_args(oc->nodemask));
 446         cpuset_print_current_mems_allowed();
 447         mem_cgroup_print_oom_context(oc->memcg, victim);
 448         pr_cont(",task=%s,pid=%d,uid=%d\n", victim->comm, victim->pid,
 449                 from_kuid(&init_user_ns, task_uid(victim)));
 450 }
 451 
 452 static void dump_header(struct oom_control *oc, struct task_struct *p)
 453 {
 454         pr_warn("%s invoked oom-killer: gfp_mask=%#x(%pGg), order=%d, oom_score_adj=%hd\n",
 455                 current->comm, oc->gfp_mask, &oc->gfp_mask, oc->order,
 456                         current->signal->oom_score_adj);
 457         if (!IS_ENABLED(CONFIG_COMPACTION) && oc->order)
 458                 pr_warn("COMPACTION is disabled!!!\n");
 459 
 460         dump_stack();
 461         if (is_memcg_oom(oc))
 462                 mem_cgroup_print_oom_meminfo(oc->memcg);
 463         else {
 464                 show_mem(SHOW_MEM_FILTER_NODES, oc->nodemask);
 465                 if (is_dump_unreclaim_slabs())
 466                         dump_unreclaimable_slab();
 467         }
 468         if (sysctl_oom_dump_tasks)
 469                 dump_tasks(oc);
 470         if (p)
 471                 dump_oom_summary(oc, p);
 472 }
 473 
 474 /*
 475  * Number of OOM victims in flight
 476  */
 477 static atomic_t oom_victims = ATOMIC_INIT(0);
 478 static DECLARE_WAIT_QUEUE_HEAD(oom_victims_wait);
 479 
 480 static bool oom_killer_disabled __read_mostly;
 481 
 482 #define K(x) ((x) << (PAGE_SHIFT-10))
 483 
 484 /*
 485  * task->mm can be NULL if the task is the exited group leader.  So to
 486  * determine whether the task is using a particular mm, we examine all the
 487  * task's threads: if one of those is using this mm then this task was also
 488  * using it.
 489  */
 490 bool process_shares_mm(struct task_struct *p, struct mm_struct *mm)
 491 {
 492         struct task_struct *t;
 493 
 494         for_each_thread(p, t) {
 495                 struct mm_struct *t_mm = READ_ONCE(t->mm);
 496                 if (t_mm)
 497                         return t_mm == mm;
 498         }
 499         return false;
 500 }
 501 
 502 #ifdef CONFIG_MMU
 503 /*
 504  * OOM Reaper kernel thread which tries to reap the memory used by the OOM
 505  * victim (if that is possible) to help the OOM killer to move on.
 506  */
 507 static struct task_struct *oom_reaper_th;
 508 static DECLARE_WAIT_QUEUE_HEAD(oom_reaper_wait);
 509 static struct task_struct *oom_reaper_list;
 510 static DEFINE_SPINLOCK(oom_reaper_lock);
 511 
 512 bool __oom_reap_task_mm(struct mm_struct *mm)
 513 {
 514         struct vm_area_struct *vma;
 515         bool ret = true;
 516 
 517         /*
 518          * Tell all users of get_user/copy_from_user etc... that the content
 519          * is no longer stable. No barriers really needed because unmapping
 520          * should imply barriers already and the reader would hit a page fault
 521          * if it stumbled over a reaped memory.
 522          */
 523         set_bit(MMF_UNSTABLE, &mm->flags);
 524 
 525         for (vma = mm->mmap ; vma; vma = vma->vm_next) {
 526                 if (!can_madv_lru_vma(vma))
 527                         continue;
 528 
 529                 /*
 530                  * Only anonymous pages have a good chance to be dropped
 531                  * without additional steps which we cannot afford as we
 532                  * are OOM already.
 533                  *
 534                  * We do not even care about fs backed pages because all
 535                  * which are reclaimable have already been reclaimed and
 536                  * we do not want to block exit_mmap by keeping mm ref
 537                  * count elevated without a good reason.
 538                  */
 539                 if (vma_is_anonymous(vma) || !(vma->vm_flags & VM_SHARED)) {
 540                         struct mmu_notifier_range range;
 541                         struct mmu_gather tlb;
 542 
 543                         mmu_notifier_range_init(&range, MMU_NOTIFY_UNMAP, 0,
 544                                                 vma, mm, vma->vm_start,
 545                                                 vma->vm_end);
 546                         tlb_gather_mmu(&tlb, mm, range.start, range.end);
 547                         if (mmu_notifier_invalidate_range_start_nonblock(&range)) {
 548                                 tlb_finish_mmu(&tlb, range.start, range.end);
 549                                 ret = false;
 550                                 continue;
 551                         }
 552                         unmap_page_range(&tlb, vma, range.start, range.end, NULL);
 553                         mmu_notifier_invalidate_range_end(&range);
 554                         tlb_finish_mmu(&tlb, range.start, range.end);
 555                 }
 556         }
 557 
 558         return ret;
 559 }
 560 
 561 /*
 562  * Reaps the address space of the give task.
 563  *
 564  * Returns true on success and false if none or part of the address space
 565  * has been reclaimed and the caller should retry later.
 566  */
 567 static bool oom_reap_task_mm(struct task_struct *tsk, struct mm_struct *mm)
 568 {
 569         bool ret = true;
 570 
 571         if (!down_read_trylock(&mm->mmap_sem)) {
 572                 trace_skip_task_reaping(tsk->pid);
 573                 return false;
 574         }
 575 
 576         /*
 577          * MMF_OOM_SKIP is set by exit_mmap when the OOM reaper can't
 578          * work on the mm anymore. The check for MMF_OOM_SKIP must run
 579          * under mmap_sem for reading because it serializes against the
 580          * down_write();up_write() cycle in exit_mmap().
 581          */
 582         if (test_bit(MMF_OOM_SKIP, &mm->flags)) {
 583                 trace_skip_task_reaping(tsk->pid);
 584                 goto out_unlock;
 585         }
 586 
 587         trace_start_task_reaping(tsk->pid);
 588 
 589         /* failed to reap part of the address space. Try again later */
 590         ret = __oom_reap_task_mm(mm);
 591         if (!ret)
 592                 goto out_finish;
 593 
 594         pr_info("oom_reaper: reaped process %d (%s), now anon-rss:%lukB, file-rss:%lukB, shmem-rss:%lukB\n",
 595                         task_pid_nr(tsk), tsk->comm,
 596                         K(get_mm_counter(mm, MM_ANONPAGES)),
 597                         K(get_mm_counter(mm, MM_FILEPAGES)),
 598                         K(get_mm_counter(mm, MM_SHMEMPAGES)));
 599 out_finish:
 600         trace_finish_task_reaping(tsk->pid);
 601 out_unlock:
 602         up_read(&mm->mmap_sem);
 603 
 604         return ret;
 605 }
 606 
 607 #define MAX_OOM_REAP_RETRIES 10
 608 static void oom_reap_task(struct task_struct *tsk)
 609 {
 610         int attempts = 0;
 611         struct mm_struct *mm = tsk->signal->oom_mm;
 612 
 613         /* Retry the down_read_trylock(mmap_sem) a few times */
 614         while (attempts++ < MAX_OOM_REAP_RETRIES && !oom_reap_task_mm(tsk, mm))
 615                 schedule_timeout_idle(HZ/10);
 616 
 617         if (attempts <= MAX_OOM_REAP_RETRIES ||
 618             test_bit(MMF_OOM_SKIP, &mm->flags))
 619                 goto done;
 620 
 621         pr_info("oom_reaper: unable to reap pid:%d (%s)\n",
 622                 task_pid_nr(tsk), tsk->comm);
 623         debug_show_all_locks();
 624 
 625 done:
 626         tsk->oom_reaper_list = NULL;
 627 
 628         /*
 629          * Hide this mm from OOM killer because it has been either reaped or
 630          * somebody can't call up_write(mmap_sem).
 631          */
 632         set_bit(MMF_OOM_SKIP, &mm->flags);
 633 
 634         /* Drop a reference taken by wake_oom_reaper */
 635         put_task_struct(tsk);
 636 }
 637 
 638 static int oom_reaper(void *unused)
 639 {
 640         while (true) {
 641                 struct task_struct *tsk = NULL;
 642 
 643                 wait_event_freezable(oom_reaper_wait, oom_reaper_list != NULL);
 644                 spin_lock(&oom_reaper_lock);
 645                 if (oom_reaper_list != NULL) {
 646                         tsk = oom_reaper_list;
 647                         oom_reaper_list = tsk->oom_reaper_list;
 648                 }
 649                 spin_unlock(&oom_reaper_lock);
 650 
 651                 if (tsk)
 652                         oom_reap_task(tsk);
 653         }
 654 
 655         return 0;
 656 }
 657 
 658 static void wake_oom_reaper(struct task_struct *tsk)
 659 {
 660         /* mm is already queued? */
 661         if (test_and_set_bit(MMF_OOM_REAP_QUEUED, &tsk->signal->oom_mm->flags))
 662                 return;
 663 
 664         get_task_struct(tsk);
 665 
 666         spin_lock(&oom_reaper_lock);
 667         tsk->oom_reaper_list = oom_reaper_list;
 668         oom_reaper_list = tsk;
 669         spin_unlock(&oom_reaper_lock);
 670         trace_wake_reaper(tsk->pid);
 671         wake_up(&oom_reaper_wait);
 672 }
 673 
 674 static int __init oom_init(void)
 675 {
 676         oom_reaper_th = kthread_run(oom_reaper, NULL, "oom_reaper");
 677         return 0;
 678 }
 679 subsys_initcall(oom_init)
 680 #else
 681 static inline void wake_oom_reaper(struct task_struct *tsk)
 682 {
 683 }
 684 #endif /* CONFIG_MMU */
 685 
 686 /**
 687  * mark_oom_victim - mark the given task as OOM victim
 688  * @tsk: task to mark
 689  *
 690  * Has to be called with oom_lock held and never after
 691  * oom has been disabled already.
 692  *
 693  * tsk->mm has to be non NULL and caller has to guarantee it is stable (either
 694  * under task_lock or operate on the current).
 695  */
 696 static void mark_oom_victim(struct task_struct *tsk)
 697 {
 698         struct mm_struct *mm = tsk->mm;
 699 
 700         WARN_ON(oom_killer_disabled);
 701         /* OOM killer might race with memcg OOM */
 702         if (test_and_set_tsk_thread_flag(tsk, TIF_MEMDIE))
 703                 return;
 704 
 705         /* oom_mm is bound to the signal struct life time. */
 706         if (!cmpxchg(&tsk->signal->oom_mm, NULL, mm)) {
 707                 mmgrab(tsk->signal->oom_mm);
 708                 set_bit(MMF_OOM_VICTIM, &mm->flags);
 709         }
 710 
 711         /*
 712          * Make sure that the task is woken up from uninterruptible sleep
 713          * if it is frozen because OOM killer wouldn't be able to free
 714          * any memory and livelock. freezing_slow_path will tell the freezer
 715          * that TIF_MEMDIE tasks should be ignored.
 716          */
 717         __thaw_task(tsk);
 718         atomic_inc(&oom_victims);
 719         trace_mark_victim(tsk->pid);
 720 }
 721 
 722 /**
 723  * exit_oom_victim - note the exit of an OOM victim
 724  */
 725 void exit_oom_victim(void)
 726 {
 727         clear_thread_flag(TIF_MEMDIE);
 728 
 729         if (!atomic_dec_return(&oom_victims))
 730                 wake_up_all(&oom_victims_wait);
 731 }
 732 
 733 /**
 734  * oom_killer_enable - enable OOM killer
 735  */
 736 void oom_killer_enable(void)
 737 {
 738         oom_killer_disabled = false;
 739         pr_info("OOM killer enabled.\n");
 740 }
 741 
 742 /**
 743  * oom_killer_disable - disable OOM killer
 744  * @timeout: maximum timeout to wait for oom victims in jiffies
 745  *
 746  * Forces all page allocations to fail rather than trigger OOM killer.
 747  * Will block and wait until all OOM victims are killed or the given
 748  * timeout expires.
 749  *
 750  * The function cannot be called when there are runnable user tasks because
 751  * the userspace would see unexpected allocation failures as a result. Any
 752  * new usage of this function should be consulted with MM people.
 753  *
 754  * Returns true if successful and false if the OOM killer cannot be
 755  * disabled.
 756  */
 757 bool oom_killer_disable(signed long timeout)
 758 {
 759         signed long ret;
 760 
 761         /*
 762          * Make sure to not race with an ongoing OOM killer. Check that the
 763          * current is not killed (possibly due to sharing the victim's memory).
 764          */
 765         if (mutex_lock_killable(&oom_lock))
 766                 return false;
 767         oom_killer_disabled = true;
 768         mutex_unlock(&oom_lock);
 769 
 770         ret = wait_event_interruptible_timeout(oom_victims_wait,
 771                         !atomic_read(&oom_victims), timeout);
 772         if (ret <= 0) {
 773                 oom_killer_enable();
 774                 return false;
 775         }
 776         pr_info("OOM killer disabled.\n");
 777 
 778         return true;
 779 }
 780 
 781 static inline bool __task_will_free_mem(struct task_struct *task)
 782 {
 783         struct signal_struct *sig = task->signal;
 784 
 785         /*
 786          * A coredumping process may sleep for an extended period in exit_mm(),
 787          * so the oom killer cannot assume that the process will promptly exit
 788          * and release memory.
 789          */
 790         if (sig->flags & SIGNAL_GROUP_COREDUMP)
 791                 return false;
 792 
 793         if (sig->flags & SIGNAL_GROUP_EXIT)
 794                 return true;
 795 
 796         if (thread_group_empty(task) && (task->flags & PF_EXITING))
 797                 return true;
 798 
 799         return false;
 800 }
 801 
 802 /*
 803  * Checks whether the given task is dying or exiting and likely to
 804  * release its address space. This means that all threads and processes
 805  * sharing the same mm have to be killed or exiting.
 806  * Caller has to make sure that task->mm is stable (hold task_lock or
 807  * it operates on the current).
 808  */
 809 static bool task_will_free_mem(struct task_struct *task)
 810 {
 811         struct mm_struct *mm = task->mm;
 812         struct task_struct *p;
 813         bool ret = true;
 814 
 815         /*
 816          * Skip tasks without mm because it might have passed its exit_mm and
 817          * exit_oom_victim. oom_reaper could have rescued that but do not rely
 818          * on that for now. We can consider find_lock_task_mm in future.
 819          */
 820         if (!mm)
 821                 return false;
 822 
 823         if (!__task_will_free_mem(task))
 824                 return false;
 825 
 826         /*
 827          * This task has already been drained by the oom reaper so there are
 828          * only small chances it will free some more
 829          */
 830         if (test_bit(MMF_OOM_SKIP, &mm->flags))
 831                 return false;
 832 
 833         if (atomic_read(&mm->mm_users) <= 1)
 834                 return true;
 835 
 836         /*
 837          * Make sure that all tasks which share the mm with the given tasks
 838          * are dying as well to make sure that a) nobody pins its mm and
 839          * b) the task is also reapable by the oom reaper.
 840          */
 841         rcu_read_lock();
 842         for_each_process(p) {
 843                 if (!process_shares_mm(p, mm))
 844                         continue;
 845                 if (same_thread_group(task, p))
 846                         continue;
 847                 ret = __task_will_free_mem(p);
 848                 if (!ret)
 849                         break;
 850         }
 851         rcu_read_unlock();
 852 
 853         return ret;
 854 }
 855 
 856 static void __oom_kill_process(struct task_struct *victim, const char *message)
 857 {
 858         struct task_struct *p;
 859         struct mm_struct *mm;
 860         bool can_oom_reap = true;
 861 
 862         p = find_lock_task_mm(victim);
 863         if (!p) {
 864                 put_task_struct(victim);
 865                 return;
 866         } else if (victim != p) {
 867                 get_task_struct(p);
 868                 put_task_struct(victim);
 869                 victim = p;
 870         }
 871 
 872         /* Get a reference to safely compare mm after task_unlock(victim) */
 873         mm = victim->mm;
 874         mmgrab(mm);
 875 
 876         /* Raise event before sending signal: task reaper must see this */
 877         count_vm_event(OOM_KILL);
 878         memcg_memory_event_mm(mm, MEMCG_OOM_KILL);
 879 
 880         /*
 881          * We should send SIGKILL before granting access to memory reserves
 882          * in order to prevent the OOM victim from depleting the memory
 883          * reserves from the user space under its control.
 884          */
 885         do_send_sig_info(SIGKILL, SEND_SIG_PRIV, victim, PIDTYPE_TGID);
 886         mark_oom_victim(victim);
 887         pr_err("%s: Killed process %d (%s) total-vm:%lukB, anon-rss:%lukB, file-rss:%lukB, shmem-rss:%lukB, UID:%u pgtables:%lukB oom_score_adj:%hd\n",
 888                 message, task_pid_nr(victim), victim->comm, K(mm->total_vm),
 889                 K(get_mm_counter(mm, MM_ANONPAGES)),
 890                 K(get_mm_counter(mm, MM_FILEPAGES)),
 891                 K(get_mm_counter(mm, MM_SHMEMPAGES)),
 892                 from_kuid(&init_user_ns, task_uid(victim)),
 893                 mm_pgtables_bytes(mm) >> 10, victim->signal->oom_score_adj);
 894         task_unlock(victim);
 895 
 896         /*
 897          * Kill all user processes sharing victim->mm in other thread groups, if
 898          * any.  They don't get access to memory reserves, though, to avoid
 899          * depletion of all memory.  This prevents mm->mmap_sem livelock when an
 900          * oom killed thread cannot exit because it requires the semaphore and
 901          * its contended by another thread trying to allocate memory itself.
 902          * That thread will now get access to memory reserves since it has a
 903          * pending fatal signal.
 904          */
 905         rcu_read_lock();
 906         for_each_process(p) {
 907                 if (!process_shares_mm(p, mm))
 908                         continue;
 909                 if (same_thread_group(p, victim))
 910                         continue;
 911                 if (is_global_init(p)) {
 912                         can_oom_reap = false;
 913                         set_bit(MMF_OOM_SKIP, &mm->flags);
 914                         pr_info("oom killer %d (%s) has mm pinned by %d (%s)\n",
 915                                         task_pid_nr(victim), victim->comm,
 916                                         task_pid_nr(p), p->comm);
 917                         continue;
 918                 }
 919                 /*
 920                  * No use_mm() user needs to read from the userspace so we are
 921                  * ok to reap it.
 922                  */
 923                 if (unlikely(p->flags & PF_KTHREAD))
 924                         continue;
 925                 do_send_sig_info(SIGKILL, SEND_SIG_PRIV, p, PIDTYPE_TGID);
 926         }
 927         rcu_read_unlock();
 928 
 929         if (can_oom_reap)
 930                 wake_oom_reaper(victim);
 931 
 932         mmdrop(mm);
 933         put_task_struct(victim);
 934 }
 935 #undef K
 936 
 937 /*
 938  * Kill provided task unless it's secured by setting
 939  * oom_score_adj to OOM_SCORE_ADJ_MIN.
 940  */
 941 static int oom_kill_memcg_member(struct task_struct *task, void *message)
 942 {
 943         if (task->signal->oom_score_adj != OOM_SCORE_ADJ_MIN &&
 944             !is_global_init(task)) {
 945                 get_task_struct(task);
 946                 __oom_kill_process(task, message);
 947         }
 948         return 0;
 949 }
 950 
 951 static void oom_kill_process(struct oom_control *oc, const char *message)
 952 {
 953         struct task_struct *victim = oc->chosen;
 954         struct mem_cgroup *oom_group;
 955         static DEFINE_RATELIMIT_STATE(oom_rs, DEFAULT_RATELIMIT_INTERVAL,
 956                                               DEFAULT_RATELIMIT_BURST);
 957 
 958         /*
 959          * If the task is already exiting, don't alarm the sysadmin or kill
 960          * its children or threads, just give it access to memory reserves
 961          * so it can die quickly
 962          */
 963         task_lock(victim);
 964         if (task_will_free_mem(victim)) {
 965                 mark_oom_victim(victim);
 966                 wake_oom_reaper(victim);
 967                 task_unlock(victim);
 968                 put_task_struct(victim);
 969                 return;
 970         }
 971         task_unlock(victim);
 972 
 973         if (__ratelimit(&oom_rs))
 974                 dump_header(oc, victim);
 975 
 976         /*
 977          * Do we need to kill the entire memory cgroup?
 978          * Or even one of the ancestor memory cgroups?
 979          * Check this out before killing the victim task.
 980          */
 981         oom_group = mem_cgroup_get_oom_group(victim, oc->memcg);
 982 
 983         __oom_kill_process(victim, message);
 984 
 985         /*
 986          * If necessary, kill all tasks in the selected memory cgroup.
 987          */
 988         if (oom_group) {
 989                 mem_cgroup_print_oom_group(oom_group);
 990                 mem_cgroup_scan_tasks(oom_group, oom_kill_memcg_member,
 991                                       (void*)message);
 992                 mem_cgroup_put(oom_group);
 993         }
 994 }
 995 
 996 /*
 997  * Determines whether the kernel must panic because of the panic_on_oom sysctl.
 998  */
 999 static void check_panic_on_oom(struct oom_control *oc)
1000 {
1001         if (likely(!sysctl_panic_on_oom))
1002                 return;
1003         if (sysctl_panic_on_oom != 2) {
1004                 /*
1005                  * panic_on_oom == 1 only affects CONSTRAINT_NONE, the kernel
1006                  * does not panic for cpuset, mempolicy, or memcg allocation
1007                  * failures.
1008                  */
1009                 if (oc->constraint != CONSTRAINT_NONE)
1010                         return;
1011         }
1012         /* Do not panic for oom kills triggered by sysrq */
1013         if (is_sysrq_oom(oc))
1014                 return;
1015         dump_header(oc, NULL);
1016         panic("Out of memory: %s panic_on_oom is enabled\n",
1017                 sysctl_panic_on_oom == 2 ? "compulsory" : "system-wide");
1018 }
1019 
1020 static BLOCKING_NOTIFIER_HEAD(oom_notify_list);
1021 
1022 int register_oom_notifier(struct notifier_block *nb)
1023 {
1024         return blocking_notifier_chain_register(&oom_notify_list, nb);
1025 }
1026 EXPORT_SYMBOL_GPL(register_oom_notifier);
1027 
1028 int unregister_oom_notifier(struct notifier_block *nb)
1029 {
1030         return blocking_notifier_chain_unregister(&oom_notify_list, nb);
1031 }
1032 EXPORT_SYMBOL_GPL(unregister_oom_notifier);
1033 
1034 /**
1035  * out_of_memory - kill the "best" process when we run out of memory
1036  * @oc: pointer to struct oom_control
1037  *
1038  * If we run out of memory, we have the choice between either
1039  * killing a random task (bad), letting the system crash (worse)
1040  * OR try to be smart about which process to kill. Note that we
1041  * don't have to be perfect here, we just have to be good.
1042  */
1043 bool out_of_memory(struct oom_control *oc)
1044 {
1045         unsigned long freed = 0;
1046 
1047         if (oom_killer_disabled)
1048                 return false;
1049 
1050         if (!is_memcg_oom(oc)) {
1051                 blocking_notifier_call_chain(&oom_notify_list, 0, &freed);
1052                 if (freed > 0)
1053                         /* Got some memory back in the last second. */
1054                         return true;
1055         }
1056 
1057         /*
1058          * If current has a pending SIGKILL or is exiting, then automatically
1059          * select it.  The goal is to allow it to allocate so that it may
1060          * quickly exit and free its memory.
1061          */
1062         if (task_will_free_mem(current)) {
1063                 mark_oom_victim(current);
1064                 wake_oom_reaper(current);
1065                 return true;
1066         }
1067 
1068         /*
1069          * The OOM killer does not compensate for IO-less reclaim.
1070          * pagefault_out_of_memory lost its gfp context so we have to
1071          * make sure exclude 0 mask - all other users should have at least
1072          * ___GFP_DIRECT_RECLAIM to get here. But mem_cgroup_oom() has to
1073          * invoke the OOM killer even if it is a GFP_NOFS allocation.
1074          */
1075         if (oc->gfp_mask && !(oc->gfp_mask & __GFP_FS) && !is_memcg_oom(oc))
1076                 return true;
1077 
1078         /*
1079          * Check if there were limitations on the allocation (only relevant for
1080          * NUMA and memcg) that may require different handling.
1081          */
1082         oc->constraint = constrained_alloc(oc);
1083         if (oc->constraint != CONSTRAINT_MEMORY_POLICY)
1084                 oc->nodemask = NULL;
1085         check_panic_on_oom(oc);
1086 
1087         if (!is_memcg_oom(oc) && sysctl_oom_kill_allocating_task &&
1088             current->mm && !oom_unkillable_task(current) &&
1089             oom_cpuset_eligible(current, oc) &&
1090             current->signal->oom_score_adj != OOM_SCORE_ADJ_MIN) {
1091                 get_task_struct(current);
1092                 oc->chosen = current;
1093                 oom_kill_process(oc, "Out of memory (oom_kill_allocating_task)");
1094                 return true;
1095         }
1096 
1097         select_bad_process(oc);
1098         /* Found nothing?!?! */
1099         if (!oc->chosen) {
1100                 dump_header(oc, NULL);
1101                 pr_warn("Out of memory and no killable processes...\n");
1102                 /*
1103                  * If we got here due to an actual allocation at the
1104                  * system level, we cannot survive this and will enter
1105                  * an endless loop in the allocator. Bail out now.
1106                  */
1107                 if (!is_sysrq_oom(oc) && !is_memcg_oom(oc))
1108                         panic("System is deadlocked on memory\n");
1109         }
1110         if (oc->chosen && oc->chosen != (void *)-1UL)
1111                 oom_kill_process(oc, !is_memcg_oom(oc) ? "Out of memory" :
1112                                  "Memory cgroup out of memory");
1113         return !!oc->chosen;
1114 }
1115 
1116 /*
1117  * The pagefault handler calls here because it is out of memory, so kill a
1118  * memory-hogging task. If oom_lock is held by somebody else, a parallel oom
1119  * killing is already in progress so do nothing.
1120  */
1121 void pagefault_out_of_memory(void)
1122 {
1123         struct oom_control oc = {
1124                 .zonelist = NULL,
1125                 .nodemask = NULL,
1126                 .memcg = NULL,
1127                 .gfp_mask = 0,
1128                 .order = 0,
1129         };
1130 
1131         if (mem_cgroup_oom_synchronize(true))
1132                 return;
1133 
1134         if (!mutex_trylock(&oom_lock))
1135                 return;
1136         out_of_memory(&oc);
1137         mutex_unlock(&oom_lock);
1138 }