FreeBSD/Linux Kernel Cross Reference
sys/mm/oom_kill.c

     /*
      *  linux/mm/oom_kill.c
      * 
      *  Copyright (C)  1998,2000  Rik van Riel
      *      Thanks go out to Claus Fischer for some serious inspiration and
      *      for goading me into coding this file...
      *  Copyright (C)  2010  Google, Inc.
      *      Rewritten by David Rientjes
      *
     *  The routines in this file are used to kill a process when
     *  we're seriously out of memory. This gets called from __alloc_pages()
     *  in mm/page_alloc.c when we really run out of memory.
     *
     *  Since we won't call these routines often (on a well-configured
     *  machine) this file will double as a 'coding guide' and a signpost
     *  for newbie kernel hackers. It features several pointers to major
     *  kernel subsystems and hints as to where to find out what things do.
     */
    
    #include <linux/oom.h>
    #include <linux/mm.h>
    #include <linux/err.h>
    #include <linux/gfp.h>
    #include <linux/sched.h>
    #include <linux/swap.h>
    #include <linux/timex.h>
    #include <linux/jiffies.h>
    #include <linux/cpuset.h>
    #include <linux/export.h>
    #include <linux/notifier.h>
    #include <linux/memcontrol.h>
    #include <linux/mempolicy.h>
    #include <linux/security.h>
    #include <linux/ptrace.h>
    #include <linux/freezer.h>
    #include <linux/ftrace.h>
    #include <linux/ratelimit.h>
    
    #define CREATE_TRACE_POINTS
    #include <trace/events/oom.h>
    
    int sysctl_panic_on_oom;
    int sysctl_oom_kill_allocating_task;
    int sysctl_oom_dump_tasks = 1;
    static DEFINE_SPINLOCK(zone_scan_lock);
    
    #ifdef CONFIG_NUMA
    /**
     * has_intersects_mems_allowed() - check task eligiblity for kill
     * @tsk: task struct of which task to consider
     * @mask: nodemask passed to page allocator for mempolicy ooms
     *
     * Task eligibility is determined by whether or not a candidate task, @tsk,
     * shares the same mempolicy nodes as current if it is bound by such a policy
     * and whether or not it has the same set of allowed cpuset nodes.
     */
    static bool has_intersects_mems_allowed(struct task_struct *tsk,
                                            const nodemask_t *mask)
    {
            struct task_struct *start = tsk;
    
            do {
                    if (mask) {
                            /*
                             * If this is a mempolicy constrained oom, tsk's
                             * cpuset is irrelevant.  Only return true if its
                             * mempolicy intersects current, otherwise it may be
                             * needlessly killed.
                             */
                            if (mempolicy_nodemask_intersects(tsk, mask))
                                    return true;
                    } else {
                            /*
                             * This is not a mempolicy constrained oom, so only
                             * check the mems of tsk's cpuset.
                             */
                            if (cpuset_mems_allowed_intersects(current, tsk))
                                    return true;
                    }
            } while_each_thread(start, tsk);
    
            return false;
    }
    #else
    static bool has_intersects_mems_allowed(struct task_struct *tsk,
                                            const nodemask_t *mask)
    {
            return true;
    }
    #endif /* CONFIG_NUMA */
    
    /*
     * The process p may have detached its own ->mm while exiting or through
     * use_mm(), but one or more of its subthreads may still have a valid
     * pointer.  Return p, or any of its subthreads with a valid ->mm, with
     * task_lock() held.
     */
    struct task_struct *find_lock_task_mm(struct task_struct *p)
    {
           struct task_struct *t = p;
   
           do {
                   task_lock(t);
                   if (likely(t->mm))
                           return t;
                   task_unlock(t);
           } while_each_thread(p, t);
   
           return NULL;
   }
   
   /* return true if the task is not adequate as candidate victim task. */
   static bool oom_unkillable_task(struct task_struct *p,
                   const struct mem_cgroup *memcg, const nodemask_t *nodemask)
   {
           if (is_global_init(p))
                   return true;
           if (p->flags & PF_KTHREAD)
                   return true;
   
           /* When mem_cgroup_out_of_memory() and p is not member of the group */
           if (memcg && !task_in_mem_cgroup(p, memcg))
                   return true;
   
           /* p may not have freeable memory in nodemask */
           if (!has_intersects_mems_allowed(p, nodemask))
                   return true;
   
           return false;
   }
   
   /**
    * oom_badness - heuristic function to determine which candidate task to kill
    * @p: task struct of which task we should calculate
    * @totalpages: total present RAM allowed for page allocation
    *
    * The heuristic for determining which task to kill is made to be as simple and
    * predictable as possible.  The goal is to return the highest value for the
    * task consuming the most memory to avoid subsequent oom failures.
    */
   unsigned long oom_badness(struct task_struct *p, struct mem_cgroup *memcg,
                             const nodemask_t *nodemask, unsigned long totalpages)
   {
           long points;
           long adj;
   
           if (oom_unkillable_task(p, memcg, nodemask))
                   return 0;
   
           p = find_lock_task_mm(p);
           if (!p)
                   return 0;
   
           adj = (long)p->signal->oom_score_adj;
           if (adj == OOM_SCORE_ADJ_MIN) {
                   task_unlock(p);
                   return 0;
           }
   
           /*
            * The baseline for the badness score is the proportion of RAM that each
            * task's rss, pagetable and swap space use.
            */
           points = get_mm_rss(p->mm) + p->mm->nr_ptes +
                    get_mm_counter(p->mm, MM_SWAPENTS);
           task_unlock(p);
   
           /*
            * Root processes get 3% bonus, just like the __vm_enough_memory()
            * implementation used by LSMs.
            */
           if (has_capability_noaudit(p, CAP_SYS_ADMIN))
                   adj -= 30;
   
           /* Normalize to oom_score_adj units */
           adj *= totalpages / 1000;
           points += adj;
   
           /*
            * Never return 0 for an eligible task regardless of the root bonus and
            * oom_score_adj (oom_score_adj can't be OOM_SCORE_ADJ_MIN here).
            */
           return points > 0 ? points : 1;
   }
   
   /*
    * Determine the type of allocation constraint.
    */
   #ifdef CONFIG_NUMA
   static enum oom_constraint constrained_alloc(struct zonelist *zonelist,
                                   gfp_t gfp_mask, nodemask_t *nodemask,
                                   unsigned long *totalpages)
   {
           struct zone *zone;
           struct zoneref *z;
           enum zone_type high_zoneidx = gfp_zone(gfp_mask);
           bool cpuset_limited = false;
           int nid;
   
           /* Default to all available memory */
           *totalpages = totalram_pages + total_swap_pages;
   
           if (!zonelist)
                   return CONSTRAINT_NONE;
           /*
            * Reach here only when __GFP_NOFAIL is used. So, we should avoid
            * to kill current.We have to random task kill in this case.
            * Hopefully, CONSTRAINT_THISNODE...but no way to handle it, now.
            */
           if (gfp_mask & __GFP_THISNODE)
                   return CONSTRAINT_NONE;
   
           /*
            * This is not a __GFP_THISNODE allocation, so a truncated nodemask in
            * the page allocator means a mempolicy is in effect.  Cpuset policy
            * is enforced in get_page_from_freelist().
            */
           if (nodemask && !nodes_subset(node_states[N_MEMORY], *nodemask)) {
                   *totalpages = total_swap_pages;
                   for_each_node_mask(nid, *nodemask)
                           *totalpages += node_spanned_pages(nid);
                   return CONSTRAINT_MEMORY_POLICY;
           }
   
           /* Check this allocation failure is caused by cpuset's wall function */
           for_each_zone_zonelist_nodemask(zone, z, zonelist,
                           high_zoneidx, nodemask)
                   if (!cpuset_zone_allowed_softwall(zone, gfp_mask))
                           cpuset_limited = true;
   
           if (cpuset_limited) {
                   *totalpages = total_swap_pages;
                   for_each_node_mask(nid, cpuset_current_mems_allowed)
                           *totalpages += node_spanned_pages(nid);
                   return CONSTRAINT_CPUSET;
           }
           return CONSTRAINT_NONE;
   }
   #else
   static enum oom_constraint constrained_alloc(struct zonelist *zonelist,
                                   gfp_t gfp_mask, nodemask_t *nodemask,
                                   unsigned long *totalpages)
   {
           *totalpages = totalram_pages + total_swap_pages;
           return CONSTRAINT_NONE;
   }
   #endif
   
   enum oom_scan_t oom_scan_process_thread(struct task_struct *task,
                   unsigned long totalpages, const nodemask_t *nodemask,
                   bool force_kill)
   {
           if (task->exit_state)
                   return OOM_SCAN_CONTINUE;
           if (oom_unkillable_task(task, NULL, nodemask))
                   return OOM_SCAN_CONTINUE;
   
           /*
            * This task already has access to memory reserves and is being killed.
            * Don't allow any other task to have access to the reserves.
            */
           if (test_tsk_thread_flag(task, TIF_MEMDIE)) {
                   if (unlikely(frozen(task)))
                           __thaw_task(task);
                   if (!force_kill)
                           return OOM_SCAN_ABORT;
           }
           if (!task->mm)
                   return OOM_SCAN_CONTINUE;
   
           /*
            * If task is allocating a lot of memory and has been marked to be
            * killed first if it triggers an oom, then select it.
            */
           if (oom_task_origin(task))
                   return OOM_SCAN_SELECT;
   
           if (task->flags & PF_EXITING && !force_kill) {
                   /*
                    * If this task is not being ptraced on exit, then wait for it
                    * to finish before killing some other task unnecessarily.
                    */
                   if (!(task->group_leader->ptrace & PT_TRACE_EXIT))
                           return OOM_SCAN_ABORT;
           }
           return OOM_SCAN_OK;
   }
   
   /*
    * Simple selection loop. We chose the process with the highest
    * number of 'points'.
    *
    * (not docbooked, we don't want this one cluttering up the manual)
    */
   static struct task_struct *select_bad_process(unsigned int *ppoints,
                   unsigned long totalpages, const nodemask_t *nodemask,
                   bool force_kill)
   {
           struct task_struct *g, *p;
           struct task_struct *chosen = NULL;
           unsigned long chosen_points = 0;
   
           rcu_read_lock();
           do_each_thread(g, p) {
                   unsigned int points;
   
                   switch (oom_scan_process_thread(p, totalpages, nodemask,
                                                   force_kill)) {
                   case OOM_SCAN_SELECT:
                           chosen = p;
                           chosen_points = ULONG_MAX;
                           /* fall through */
                   case OOM_SCAN_CONTINUE:
                           continue;
                   case OOM_SCAN_ABORT:
                           rcu_read_unlock();
                           return ERR_PTR(-1UL);
                   case OOM_SCAN_OK:
                           break;
                   };
                   points = oom_badness(p, NULL, nodemask, totalpages);
                   if (points > chosen_points) {
                           chosen = p;
                           chosen_points = points;
                   }
           } while_each_thread(g, p);
           if (chosen)
                   get_task_struct(chosen);
           rcu_read_unlock();
   
           *ppoints = chosen_points * 1000 / totalpages;
           return chosen;
   }
   
   /**
    * dump_tasks - dump current memory state of all system tasks
    * @memcg: current's memory controller, if constrained
    * @nodemask: nodemask passed to page allocator for mempolicy ooms
    *
    * Dumps the current memory state of all eligible tasks.  Tasks not in the same
    * memcg, not in the same cpuset, or bound to a disjoint set of mempolicy nodes
    * are not shown.
    * State information includes task's pid, uid, tgid, vm size, rss, nr_ptes,
    * swapents, oom_score_adj value, and name.
    */
   static void dump_tasks(const struct mem_cgroup *memcg, const nodemask_t *nodemask)
   {
           struct task_struct *p;
           struct task_struct *task;
   
           pr_info("[ pid ]   uid  tgid total_vm      rss nr_ptes swapents oom_score_adj name\n");
           rcu_read_lock();
           for_each_process(p) {
                   if (oom_unkillable_task(p, memcg, nodemask))
                           continue;
   
                   task = find_lock_task_mm(p);
                   if (!task) {
                           /*
                            * This is a kthread or all of p's threads have already
                            * detached their mm's.  There's no need to report
                            * them; they can't be oom killed anyway.
                            */
                           continue;
                   }
   
                   pr_info("[%5d] %5d %5d %8lu %8lu %7lu %8lu         %5hd %s\n",
                           task->pid, from_kuid(&init_user_ns, task_uid(task)),
                           task->tgid, task->mm->total_vm, get_mm_rss(task->mm),
                           task->mm->nr_ptes,
                           get_mm_counter(task->mm, MM_SWAPENTS),
                           task->signal->oom_score_adj, task->comm);
                   task_unlock(task);
           }
           rcu_read_unlock();
   }
   
   static void dump_header(struct task_struct *p, gfp_t gfp_mask, int order,
                           struct mem_cgroup *memcg, const nodemask_t *nodemask)
   {
           task_lock(current);
           pr_warning("%s invoked oom-killer: gfp_mask=0x%x, order=%d, "
                   "oom_score_adj=%hd\n",
                   current->comm, gfp_mask, order,
                   current->signal->oom_score_adj);
           cpuset_print_task_mems_allowed(current);
           task_unlock(current);
           dump_stack();
           mem_cgroup_print_oom_info(memcg, p);
           show_mem(SHOW_MEM_FILTER_NODES);
           if (sysctl_oom_dump_tasks)
                   dump_tasks(memcg, nodemask);
   }
   
   #define K(x) ((x) << (PAGE_SHIFT-10))
   /*
    * Must be called while holding a reference to p, which will be released upon
    * returning.
    */
   void oom_kill_process(struct task_struct *p, gfp_t gfp_mask, int order,
                         unsigned int points, unsigned long totalpages,
                         struct mem_cgroup *memcg, nodemask_t *nodemask,
                         const char *message)
   {
           struct task_struct *victim = p;
           struct task_struct *child;
           struct task_struct *t = p;
           struct mm_struct *mm;
           unsigned int victim_points = 0;
           static DEFINE_RATELIMIT_STATE(oom_rs, DEFAULT_RATELIMIT_INTERVAL,
                                                 DEFAULT_RATELIMIT_BURST);
   
           /*
            * If the task is already exiting, don't alarm the sysadmin or kill
            * its children or threads, just set TIF_MEMDIE so it can die quickly
            */
           if (p->flags & PF_EXITING) {
                   set_tsk_thread_flag(p, TIF_MEMDIE);
                   put_task_struct(p);
                   return;
           }
   
           if (__ratelimit(&oom_rs))
                   dump_header(p, gfp_mask, order, memcg, nodemask);
   
           task_lock(p);
           pr_err("%s: Kill process %d (%s) score %d or sacrifice child\n",
                   message, task_pid_nr(p), p->comm, points);
           task_unlock(p);
   
           /*
            * If any of p's children has a different mm and is eligible for kill,
            * the one with the highest oom_badness() score is sacrificed for its
            * parent.  This attempts to lose the minimal amount of work done while
            * still freeing memory.
            */
           read_lock(&tasklist_lock);
           do {
                   list_for_each_entry(child, &t->children, sibling) {
                           unsigned int child_points;
   
                           if (child->mm == p->mm)
                                   continue;
                           /*
                            * oom_badness() returns 0 if the thread is unkillable
                            */
                           child_points = oom_badness(child, memcg, nodemask,
                                                                   totalpages);
                           if (child_points > victim_points) {
                                   put_task_struct(victim);
                                   victim = child;
                                   victim_points = child_points;
                                   get_task_struct(victim);
                           }
                   }
           } while_each_thread(p, t);
           read_unlock(&tasklist_lock);
   
           rcu_read_lock();
           p = find_lock_task_mm(victim);
           if (!p) {
                   rcu_read_unlock();
                   put_task_struct(victim);
                   return;
           } else if (victim != p) {
                   get_task_struct(p);
                   put_task_struct(victim);
                   victim = p;
           }
   
           /* mm cannot safely be dereferenced after task_unlock(victim) */
           mm = victim->mm;
           pr_err("Killed process %d (%s) total-vm:%lukB, anon-rss:%lukB, file-rss:%lukB\n",
                   task_pid_nr(victim), victim->comm, K(victim->mm->total_vm),
                   K(get_mm_counter(victim->mm, MM_ANONPAGES)),
                   K(get_mm_counter(victim->mm, MM_FILEPAGES)));
           task_unlock(victim);
   
           /*
            * Kill all user processes sharing victim->mm in other thread groups, if
            * any.  They don't get access to memory reserves, though, to avoid
            * depletion of all memory.  This prevents mm->mmap_sem livelock when an
            * oom killed thread cannot exit because it requires the semaphore and
            * its contended by another thread trying to allocate memory itself.
            * That thread will now get access to memory reserves since it has a
            * pending fatal signal.
            */
           for_each_process(p)
                   if (p->mm == mm && !same_thread_group(p, victim) &&
                       !(p->flags & PF_KTHREAD)) {
                           if (p->signal->oom_score_adj == OOM_SCORE_ADJ_MIN)
                                   continue;
   
                           task_lock(p);   /* Protect ->comm from prctl() */
                           pr_err("Kill process %d (%s) sharing same memory\n",
                                   task_pid_nr(p), p->comm);
                           task_unlock(p);
                           do_send_sig_info(SIGKILL, SEND_SIG_FORCED, p, true);
                   }
           rcu_read_unlock();
   
           set_tsk_thread_flag(victim, TIF_MEMDIE);
           do_send_sig_info(SIGKILL, SEND_SIG_FORCED, victim, true);
           put_task_struct(victim);
   }
   #undef K
   
   /*
    * Determines whether the kernel must panic because of the panic_on_oom sysctl.
    */
   void check_panic_on_oom(enum oom_constraint constraint, gfp_t gfp_mask,
                           int order, const nodemask_t *nodemask)
   {
           if (likely(!sysctl_panic_on_oom))
                   return;
           if (sysctl_panic_on_oom != 2) {
                   /*
                    * panic_on_oom == 1 only affects CONSTRAINT_NONE, the kernel
                    * does not panic for cpuset, mempolicy, or memcg allocation
                    * failures.
                    */
                   if (constraint != CONSTRAINT_NONE)
                           return;
           }
           dump_header(NULL, gfp_mask, order, NULL, nodemask);
           panic("Out of memory: %s panic_on_oom is enabled\n",
                   sysctl_panic_on_oom == 2 ? "compulsory" : "system-wide");
   }
   
   static BLOCKING_NOTIFIER_HEAD(oom_notify_list);
   
   int register_oom_notifier(struct notifier_block *nb)
   {
           return blocking_notifier_chain_register(&oom_notify_list, nb);
   }
   EXPORT_SYMBOL_GPL(register_oom_notifier);
   
   int unregister_oom_notifier(struct notifier_block *nb)
   {
           return blocking_notifier_chain_unregister(&oom_notify_list, nb);
   }
   EXPORT_SYMBOL_GPL(unregister_oom_notifier);
   
   /*
    * Try to acquire the OOM killer lock for the zones in zonelist.  Returns zero
    * if a parallel OOM killing is already taking place that includes a zone in
    * the zonelist.  Otherwise, locks all zones in the zonelist and returns 1.
    */
   int try_set_zonelist_oom(struct zonelist *zonelist, gfp_t gfp_mask)
   {
           struct zoneref *z;
           struct zone *zone;
           int ret = 1;
   
           spin_lock(&zone_scan_lock);
           for_each_zone_zonelist(zone, z, zonelist, gfp_zone(gfp_mask)) {
                   if (zone_is_oom_locked(zone)) {
                           ret = 0;
                           goto out;
                   }
           }
   
           for_each_zone_zonelist(zone, z, zonelist, gfp_zone(gfp_mask)) {
                   /*
                    * Lock each zone in the zonelist under zone_scan_lock so a
                    * parallel invocation of try_set_zonelist_oom() doesn't succeed
                    * when it shouldn't.
                    */
                   zone_set_flag(zone, ZONE_OOM_LOCKED);
           }
   
   out:
           spin_unlock(&zone_scan_lock);
           return ret;
   }
   
   /*
    * Clears the ZONE_OOM_LOCKED flag for all zones in the zonelist so that failed
    * allocation attempts with zonelists containing them may now recall the OOM
    * killer, if necessary.
    */
   void clear_zonelist_oom(struct zonelist *zonelist, gfp_t gfp_mask)
   {
           struct zoneref *z;
           struct zone *zone;
   
           spin_lock(&zone_scan_lock);
           for_each_zone_zonelist(zone, z, zonelist, gfp_zone(gfp_mask)) {
                   zone_clear_flag(zone, ZONE_OOM_LOCKED);
           }
           spin_unlock(&zone_scan_lock);
   }
   
   /**
    * out_of_memory - kill the "best" process when we run out of memory
    * @zonelist: zonelist pointer
    * @gfp_mask: memory allocation flags
    * @order: amount of memory being requested as a power of 2
    * @nodemask: nodemask passed to page allocator
    * @force_kill: true if a task must be killed, even if others are exiting
    *
    * If we run out of memory, we have the choice between either
    * killing a random task (bad), letting the system crash (worse)
    * OR try to be smart about which process to kill. Note that we
    * don't have to be perfect here, we just have to be good.
    */
   void out_of_memory(struct zonelist *zonelist, gfp_t gfp_mask,
                   int order, nodemask_t *nodemask, bool force_kill)
   {
           const nodemask_t *mpol_mask;
           struct task_struct *p;
           unsigned long totalpages;
           unsigned long freed = 0;
           unsigned int uninitialized_var(points);
           enum oom_constraint constraint = CONSTRAINT_NONE;
           int killed = 0;
   
           blocking_notifier_call_chain(&oom_notify_list, 0, &freed);
           if (freed > 0)
                   /* Got some memory back in the last second. */
                   return;
   
           /*
            * If current has a pending SIGKILL or is exiting, then automatically
            * select it.  The goal is to allow it to allocate so that it may
            * quickly exit and free its memory.
            */
           if (fatal_signal_pending(current) || current->flags & PF_EXITING) {
                   set_thread_flag(TIF_MEMDIE);
                   return;
           }
   
           /*
            * Check if there were limitations on the allocation (only relevant for
            * NUMA) that may require different handling.
            */
           constraint = constrained_alloc(zonelist, gfp_mask, nodemask,
                                                   &totalpages);
           mpol_mask = (constraint == CONSTRAINT_MEMORY_POLICY) ? nodemask : NULL;
           check_panic_on_oom(constraint, gfp_mask, order, mpol_mask);
   
           if (sysctl_oom_kill_allocating_task && current->mm &&
               !oom_unkillable_task(current, NULL, nodemask) &&
               current->signal->oom_score_adj != OOM_SCORE_ADJ_MIN) {
                   get_task_struct(current);
                   oom_kill_process(current, gfp_mask, order, 0, totalpages, NULL,
                                    nodemask,
                                    "Out of memory (oom_kill_allocating_task)");
                   goto out;
           }
   
           p = select_bad_process(&points, totalpages, mpol_mask, force_kill);
           /* Found nothing?!?! Either we hang forever, or we panic. */
           if (!p) {
                   dump_header(NULL, gfp_mask, order, NULL, mpol_mask);
                   panic("Out of memory and no killable processes...\n");
           }
           if (PTR_ERR(p) != -1UL) {
                   oom_kill_process(p, gfp_mask, order, points, totalpages, NULL,
                                    nodemask, "Out of memory");
                   killed = 1;
           }
   out:
           /*
            * Give the killed threads a good chance of exiting before trying to
            * allocate memory again.
            */
           if (killed)
                   schedule_timeout_killable(1);
   }
   
   /*
    * The pagefault handler calls here because it is out of memory, so kill a
    * memory-hogging task.  If any populated zone has ZONE_OOM_LOCKED set, a
    * parallel oom killing is already in progress so do nothing.
    */
   void pagefault_out_of_memory(void)
   {
           struct zonelist *zonelist = node_zonelist(first_online_node,
                                                     GFP_KERNEL);
   
           if (try_set_zonelist_oom(zonelist, GFP_KERNEL)) {
                   out_of_memory(NULL, 0, 0, NULL, false);
                   clear_zonelist_oom(zonelist, GFP_KERNEL);
           }
   }

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