oom_kill.c

Go to the documentation of this file.

/*
 *  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);

/*
 * compare_swap_oom_score_adj() - compare and swap current's oom_score_adj
 * @old_val: old oom_score_adj for compare
 * @new_val: new oom_score_adj for swap
 *
 * Sets the oom_score_adj value for current to @new_val iff its present value is
 * @old_val.  Usually used to reinstate a previous value to prevent racing with
 * userspacing tuning the value in the interim.
 */
void compare_swap_oom_score_adj(int old_val, int new_val)
{
    struct sighand_struct *sighand = current->sighand;

    spin_lock_irq(&sighand->siglock);
    if (current->signal->oom_score_adj == old_val)
        current->signal->oom_score_adj = new_val;
    trace_oom_score_adj_update(current);
    spin_unlock_irq(&sighand->siglock);
}

int test_set_oom_score_adj(int new_val)
{
    struct sighand_struct *sighand = current->sighand;
    int old_val;

    spin_lock_irq(&sighand->siglock);
    old_val = current->signal->oom_score_adj;
    current->signal->oom_score_adj = new_val;
    trace_oom_score_adj_update(current);
    spin_unlock_irq(&sighand->siglock);

    return old_val;
}

#ifdef CONFIG_NUMA

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;
}

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 = 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_HIGH_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->flags & PF_EXITING) {
        /*
         * If task is current and is in the process of releasing memory,
         * allow the "kill" to set TIF_MEMDIE, which will allow it to
         * access memory reserves.  Otherwise, it may stall forever.
         *
         * The iteration isn't broken here, however, in case other
         * threads are found to have already been oom killed.
         */
        if (task == current)
            return OOM_SCAN_SELECT;
        else if (!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;
}

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         %5d %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=%d\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);
}

/*
 * Try to acquire the oom killer lock for all system zones.  Returns zero if a
 * parallel oom killing is taking place, otherwise locks all zones and returns
 * non-zero.
 */
static int try_set_system_oom(void)
{
    struct zone *zone;
    int ret = 1;

    spin_lock(&zone_scan_lock);
    for_each_populated_zone(zone)
        if (zone_is_oom_locked(zone)) {
            ret = 0;
            goto out;
        }
    for_each_populated_zone(zone)
        zone_set_flag(zone, ZONE_OOM_LOCKED);
out:
    spin_unlock(&zone_scan_lock);
    return ret;
}

/*
 * Clears ZONE_OOM_LOCKED for all system zones so that failed allocation
 * attempts or page faults may now recall the oom killer, if necessary.
 */
static void clear_system_oom(void)
{
    struct zone *zone;

    spin_lock(&zone_scan_lock);
    for_each_populated_zone(zone)
        zone_clear_flag(zone, ZONE_OOM_LOCKED);
    spin_unlock(&zone_scan_lock);
}

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, 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)) {
        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 a populated zone has ZONE_OOM_LOCKED set, a parallel
 * oom killing is already in progress so do nothing.  If a task is found with
 * TIF_MEMDIE set, it has been killed so do nothing and allow it to exit.
 */
void pagefault_out_of_memory(void)
{
    if (try_set_system_oom()) {
        out_of_memory(NULL, 0, 0, NULL, false);
        clear_system_oom();
    }
    schedule_timeout_killable(1);
}