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    SubjectRe: [PATCH v8] oom_kill.c: futex: Don't OOM reap the VMA containing the robust_list_head
    From
    > diff --git a/mm/oom_kill.c b/mm/oom_kill.c
    > index 7ec38194f8e1..be6d65ead7ec 100644
    > --- a/mm/oom_kill.c
    > +++ b/mm/oom_kill.c
    > @@ -632,7 +632,7 @@ static void oom_reap_task(struct task_struct *tsk)
    > */
    > set_bit(MMF_OOM_SKIP, &mm->flags);
    >
    > - /* Drop a reference taken by wake_oom_reaper */
    > + /* Drop a reference taken by queue_oom_repaer */
    > put_task_struct(tsk);
    > }
    >
    > @@ -644,12 +644,12 @@ static int oom_reaper(void *unused)
    > struct task_struct *tsk = NULL;
    >
    > wait_event_freezable(oom_reaper_wait, oom_reaper_list != NULL);
    > - spin_lock(&oom_reaper_lock);
    > + spin_lock_irq(&oom_reaper_lock);
    > if (oom_reaper_list != NULL) {
    > tsk = oom_reaper_list;
    > oom_reaper_list = tsk->oom_reaper_list;
    > }
    > - spin_unlock(&oom_reaper_lock);
    > + spin_unlock_irq(&oom_reaper_lock);
    >
    > if (tsk)
    > oom_reap_task(tsk);
    > @@ -658,22 +658,50 @@ static int oom_reaper(void *unused)
    > return 0;
    > }
    >
    > -static void wake_oom_reaper(struct task_struct *tsk)
    > +static void wake_oom_reaper_fn(struct timer_list *timer)
    > {
    > - /* mm is already queued? */
    > - if (test_and_set_bit(MMF_OOM_REAP_QUEUED, &tsk->signal->oom_mm->flags))
    > - return;
    > + struct task_struct *tsk = container_of(timer, struct task_struct, oom_reaper_timer);
    > + struct mm_struct *mm = tsk->signal->oom_mm;
    > + unsigned long flags;
    >
    > - get_task_struct(tsk);
    > + /* The victim managed to terminate on its own - see exit_mmap */
    > + if (test_bit(MMF_OOM_SKIP, &mm->flags)) {
    > + put_task_struct(tsk);
    > + return;
    > + }
    >
    > - spin_lock(&oom_reaper_lock);
    > + spin_lock_irqsave(&oom_reaper_lock, flags);
    > tsk->oom_reaper_list = oom_reaper_list;
    > oom_reaper_list = tsk;
    > - spin_unlock(&oom_reaper_lock);
    > + spin_unlock_irqrestore(&oom_reaper_lock, flags);
    > trace_wake_reaper(tsk->pid);
    > wake_up(&oom_reaper_wait);
    > }
    >
    > +/*
    > + * Give OOM victims some head room to exit themselves. If they do not exit
    > + * on their own the oom reaper is invoked.
    > + * The timeout is basically arbitrary and there is no best value to use.
    > + * The longer it will be the longer the worst case scenario OOM can
    > + * take. The smaller the timeout the more likely the oom_reaper can get
    > + * into the way and release resources which could be needed during the
    > + * exit path - e.g. futex robust lists can sit in the anonymous memory
    > + * which could be reaped and the exit path won't be able to let waiters
    > + * know the holding task has terminated.
    > + */
    > +#define OOM_REAPER_DELAY (2*HZ)
    > +static void queue_oom_repaer(struct task_struct *tsk)
    > +{
    > + /* mm is already queued? */
    > + if (test_and_set_bit(MMF_OOM_REAP_QUEUED, &tsk->signal->oom_mm->flags))
    > + return;
    > +
    > + get_task_struct(tsk);
    > + timer_setup(&tsk->oom_reaper_timer, wake_oom_reaper_fn, 0);
    > + tsk->oom_reaper_timer.expires = jiffies + OOM_REAPER_DELAY;
    > + add_timer(&tsk->oom_reaper_timer);
    > +}
    > +
    > static int __init oom_init(void)
    > {
    > oom_reaper_th = kthread_run(oom_reaper, NULL, "oom_reaper");
    > @@ -681,7 +709,7 @@ static int __init oom_init(void)
    > }
    > subsys_initcall(oom_init)
    > #else
    > -static inline void wake_oom_reaper(struct task_struct *tsk)
    > +static inline void queue_oom_repaer(struct task_struct *tsk)
    > {
    > }
    > #endif /* CONFIG_MMU */
    > @@ -932,7 +960,7 @@ static void __oom_kill_process(struct task_struct *victim, const char *message)
    > rcu_read_unlock();
    >
    > if (can_oom_reap)
    > - wake_oom_reaper(victim);
    > + queue_oom_repaer(victim);
    >
    > mmdrop(mm);
    > put_task_struct(victim);
    > @@ -968,7 +996,7 @@ static void oom_kill_process(struct oom_control *oc, const char *message)
    > task_lock(victim);
    > if (task_will_free_mem(victim)) {
    > mark_oom_victim(victim);
    > - wake_oom_reaper(victim);
    > + queue_oom_repaer(victim);
    > task_unlock(victim);
    > put_task_struct(victim);
    > return;
    > @@ -1067,7 +1095,7 @@ bool out_of_memory(struct oom_control *oc)
    > */
    > if (task_will_free_mem(current)) {
    > mark_oom_victim(current);
    > - wake_oom_reaper(current);
    > + queue_oom_repaer(current);
    > return true;
    > }

    Thanks for the code Michal-- It does seem to fix our issue! I will post it after
    I finish running it through a few more test cases, and our internal testing suites.

    Cheers,
    -- Nico

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