[cascardo/linux.git] / 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
 * @start: 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 *start,
                                        const nodemask_t *mask)
{
        struct task_struct *tsk;
        bool ret = false;

        rcu_read_lock();
        for_each_thread(start, tsk) {
                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.
                         */
                        ret = mempolicy_nodemask_intersects(tsk, mask);
                } else {
                        /*
                         * This is not a mempolicy constrained oom, so only
                         * check the mems of tsk's cpuset.
                         */
                        ret = cpuset_mems_allowed_intersects(current, tsk);
                }
                if (ret)
                        break;
        }
        rcu_read_unlock();

        return ret;
}
#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;

        rcu_read_lock();

        for_each_thread(p, t) {
                task_lock(t);
                if (likely(t->mm))
                        goto found;
                task_unlock(t);
        }
        t = NULL;
found:
        rcu_read_unlock();

        return t;
}

/* return true if the task is not adequate as candidate victim task. */
static bool oom_unkillable_task(struct task_struct *p,
                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) + get_mm_counter(p->mm, MM_SWAPENTS) +
                atomic_long_read(&p->mm->nr_ptes) + mm_nr_pmds(p->mm);
        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))
                points -= (points * 3) / 100;

        /* 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(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 (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 (!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_will_free_mem(task) && !force_kill)
                return OOM_SCAN_ABORT;

        return OOM_SCAN_OK;
}

/*
 * Simple selection loop. We chose the process with the highest
 * number of 'points'.  Returns -1 on scan abort.
 *
 * (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();
        for_each_process_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 (struct task_struct *)(-1UL);
                case OOM_SCAN_OK:
                        break;
                };
                points = oom_badness(p, NULL, nodemask, totalpages);
                if (!points || points < chosen_points)
                        continue;
                /* Prefer thread group leaders for display purposes */
                if (points == chosen_points && thread_group_leader(chosen))
                        continue;

                chosen = p;
                chosen_points = points;
        }
        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(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 nr_pmds 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 %7ld %7ld %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),
                        atomic_long_read(&task->mm->nr_ptes),
                        mm_nr_pmds(task->mm),
                        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();
        if (memcg)
                mem_cgroup_print_oom_info(memcg, p);
        else
                show_mem(SHOW_MEM_FILTER_NODES);
        if (sysctl_oom_dump_tasks)
                dump_tasks(memcg, nodemask);
}

/*
 * Number of OOM victims in flight
 */
static atomic_t oom_victims = ATOMIC_INIT(0);
static DECLARE_WAIT_QUEUE_HEAD(oom_victims_wait);

bool oom_killer_disabled __read_mostly;
static DECLARE_RWSEM(oom_sem);

/**
 * mark_oom_victim - mark the given task as OOM victim
 * @tsk: task to mark
 *
 * Has to be called with oom_sem taken for read and never after
 * oom has been disabled already.
 */
void mark_oom_victim(struct task_struct *tsk)
{
        WARN_ON(oom_killer_disabled);
        /* OOM killer might race with memcg OOM */
        if (test_and_set_tsk_thread_flag(tsk, TIF_MEMDIE))
                return;
        /*
         * Make sure that the task is woken up from uninterruptible sleep
         * if it is frozen because OOM killer wouldn't be able to free
         * any memory and livelock. freezing_slow_path will tell the freezer
         * that TIF_MEMDIE tasks should be ignored.
         */
        __thaw_task(tsk);
        atomic_inc(&oom_victims);
}

/**
 * exit_oom_victim - note the exit of an OOM victim
 */
void exit_oom_victim(void)
{
        if (!test_and_clear_thread_flag(TIF_MEMDIE))
                return;

        down_read(&oom_sem);
        /*
         * There is no need to signal the lasst oom_victim if there
         * is nobody who cares.
         */
        if (!atomic_dec_return(&oom_victims) && oom_killer_disabled)
                wake_up_all(&oom_victims_wait);
        up_read(&oom_sem);
}

/**
 * oom_killer_disable - disable OOM killer
 *
 * Forces all page allocations to fail rather than trigger OOM killer.
 * Will block and wait until all OOM victims are killed.
 *
 * The function cannot be called when there are runnable user tasks because
 * the userspace would see unexpected allocation failures as a result. Any
 * new usage of this function should be consulted with MM people.
 *
 * Returns true if successful and false if the OOM killer cannot be
 * disabled.
 */
bool oom_killer_disable(void)
{
        /*
         * Make sure to not race with an ongoing OOM killer
         * and that the current is not the victim.
         */
        down_write(&oom_sem);
        if (test_thread_flag(TIF_MEMDIE)) {
                up_write(&oom_sem);
                return false;
        }

        oom_killer_disabled = true;
        up_write(&oom_sem);

        wait_event(oom_victims_wait, !atomic_read(&oom_victims));

        return true;
}

/**
 * oom_killer_enable - enable OOM killer
 */
void oom_killer_enable(void)
{
        oom_killer_disabled = false;
}

#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;
        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
         */
        task_lock(p);
        if (p->mm && task_will_free_mem(p)) {
                mark_oom_victim(p);
                task_unlock(p);
                put_task_struct(p);
                return;
        }
        task_unlock(p);

        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);
        for_each_thread(p, t) {
                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);
                        }
                }
        }
        read_unlock(&tasklist_lock);

        p = find_lock_task_mm(victim);
        if (!p) {
                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;
        mark_oom_victim(victim);
        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.
         */
        rcu_read_lock();
        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();

        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,
                        struct mem_cgroup *memcg)
{
        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, memcg, 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.
 */
bool oom_zonelist_trylock(struct zonelist *zonelist, gfp_t gfp_mask)
{
        struct zoneref *z;
        struct zone *zone;
        bool ret = true;

        spin_lock(&zone_scan_lock);
        for_each_zone_zonelist(zone, z, zonelist, gfp_zone(gfp_mask))
                if (test_bit(ZONE_OOM_LOCKED, &zone->flags)) {
                        ret = false;
                        goto out;
                }

        /*
         * Lock each zone in the zonelist under zone_scan_lock so a parallel
         * call to oom_zonelist_trylock() doesn't succeed when it shouldn't.
         */
        for_each_zone_zonelist(zone, z, zonelist, gfp_zone(gfp_mask))
                set_bit(ZONE_OOM_LOCKED, &zone->flags);

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 oom_zonelist_unlock(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))
                clear_bit(ZONE_OOM_LOCKED, &zone->flags);
        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.
 */
static 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.
         *
         * But don't select if current has already released its mm and cleared
         * TIF_MEMDIE flag at exit_mm(), otherwise an OOM livelock may occur.
         */
        if (current->mm &&
            (fatal_signal_pending(current) || task_will_free_mem(current))) {
                mark_oom_victim(current);
                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, NULL);

        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 (p != (void *)-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);
}

/**
 * out_of_memory -  tries to invoke OOM killer.
 * @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
 *
 * invokes __out_of_memory if the OOM is not disabled by oom_killer_disable()
 * when it returns false. Otherwise returns true.
 */
bool out_of_memory(struct zonelist *zonelist, gfp_t gfp_mask,
                int order, nodemask_t *nodemask, bool force_kill)
{
        bool ret = false;

        down_read(&oom_sem);
        if (!oom_killer_disabled) {
                __out_of_memory(zonelist, gfp_mask, order, nodemask, force_kill);
                ret = true;
        }
        up_read(&oom_sem);

        return ret;
}

/*
 * 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;

        down_read(&oom_sem);
        if (mem_cgroup_oom_synchronize(true))
                goto unlock;

        zonelist = node_zonelist(first_memory_node, GFP_KERNEL);
        if (oom_zonelist_trylock(zonelist, GFP_KERNEL)) {
                if (!oom_killer_disabled)
                        __out_of_memory(NULL, 0, 0, NULL, false);
                else
                        /*
                         * There shouldn't be any user tasks runable while the
                         * OOM killer is disabled so the current task has to
                         * be a racing OOM victim for which oom_killer_disable()
                         * is waiting for.
                         */
                        WARN_ON(test_thread_flag(TIF_MEMDIE));

                oom_zonelist_unlock(zonelist, GFP_KERNEL);
        }
unlock:
        up_read(&oom_sem);
}