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Message-ID: <YmABoUYOPqhVTCBl@dhcp22.suse.cz>
Date: Wed, 20 Apr 2022 14:50:41 +0200
From: Michal Hocko <mhocko@...e.com>
To: Nico Pache <npache@...hat.com>
Cc: linux-mm@...ck.org, linux-kernel@...r.kernel.org,
Rafael Aquini <aquini@...hat.com>,
Waiman Long <longman@...hat.com>,
"Herton R . Krzesinski" <herton@...hat.com>,
Juri Lelli <juri.lelli@...hat.com>,
Vincent Guittot <vincent.guittot@...aro.org>,
Dietmar Eggemann <dietmar.eggemann@....com>,
Steven Rostedt <rostedt@...dmis.org>,
Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
Daniel Bristot de Oliveira <bristot@...hat.com>,
David Rientjes <rientjes@...gle.com>,
Andrea Arcangeli <aarcange@...hat.com>,
Andrew Morton <akpm@...ux-foundation.org>,
Davidlohr Bueso <dave@...olabs.net>,
Peter Zijlstra <peterz@...radead.org>,
Ingo Molnar <mingo@...hat.com>,
Joel Savitz <jsavitz@...hat.com>,
Darren Hart <dvhart@...radead.org>, stable@...nel.org,
Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH v9] oom_kill.c: futex: Delay the OOM reaper to allow time
for proper futex cleanup
On Thu 14-04-22 10:40:42, Nico Pache wrote:
> The pthread struct is allocated on PRIVATE|ANONYMOUS memory [1] which can
> be targeted by the oom reaper. This mapping is used to store the futex
> robust list head; the kernel does not keep a copy of the robust list and
> instead references a userspace address to maintain the robustness during
> a process death. A race can occur between exit_mm and the oom reaper that
> allows the oom reaper to free the memory of the futex robust list before
> the exit path has handled the futex death:
>
> CPU1 CPU2
> ------------------------------------------------------------------------
> page_fault
> do_exit "signal"
> wake_oom_reaper
> oom_reaper
> oom_reap_task_mm (invalidates mm)
> exit_mm
> exit_mm_release
> futex_exit_release
> futex_cleanup
> exit_robust_list
> get_user (EFAULT- can't access memory)
>
> If the get_user EFAULT's, the kernel will be unable to recover the
> waiters on the robust_list, leaving userspace mutexes hung indefinitely.
>
> Delay the OOM reaper, allowing more time for the exit path to perform
> the futex cleanup.
>
> Reproducer: https://gitlab.com/jsavitz/oom_futex_reproducer
>
> [1] https://elixir.bootlin.com/glibc/latest/source/nptl/allocatestack.c#L370
>
> Fixes: 212925802454 ("mm: oom: let oom_reap_task and exit_mmap run concurrently")
> Cc: Rafael Aquini <aquini@...hat.com>
> Cc: Waiman Long <longman@...hat.com>
> Cc: Herton R. Krzesinski <herton@...hat.com>
> Cc: Juri Lelli <juri.lelli@...hat.com>
> Cc: Vincent Guittot <vincent.guittot@...aro.org>
> Cc: Dietmar Eggemann <dietmar.eggemann@....com>
> Cc: Steven Rostedt <rostedt@...dmis.org>
> Cc: Ben Segall <bsegall@...gle.com>
> Cc: Mel Gorman <mgorman@...e.de>
> Cc: Daniel Bristot de Oliveira <bristot@...hat.com>
> Cc: David Rientjes <rientjes@...gle.com>
> Cc: Michal Hocko <mhocko@...e.com>
> Cc: Andrea Arcangeli <aarcange@...hat.com>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: Davidlohr Bueso <dave@...olabs.net>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Ingo Molnar <mingo@...hat.com>
> Cc: Joel Savitz <jsavitz@...hat.com>
> Cc: Darren Hart <dvhart@...radead.org>
> Cc: stable@...nel.org
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Suggested-by: Thomas Gleixner <tglx@...utronix.de>
> [ Based on a patch by Michal Hocko ]
> Co-developed-by: Joel Savitz <jsavitz@...hat.com>
> Signed-off-by: Joel Savitz <jsavitz@...hat.com>
> Signed-off-by: Nico Pache <npache@...hat.com>
Acked-by: Michal Hocko <mhocko@...e.com>
Thanks!
> ---
> include/linux/sched.h | 1 +
> mm/oom_kill.c | 54 ++++++++++++++++++++++++++++++++-----------
> 2 files changed, 41 insertions(+), 14 deletions(-)
>
> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index d5e3c00b74e1..a8911b1f35aa 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -1443,6 +1443,7 @@ struct task_struct {
> int pagefault_disabled;
> #ifdef CONFIG_MMU
> struct task_struct *oom_reaper_list;
> + struct timer_list oom_reaper_timer;
> #endif
> #ifdef CONFIG_VMAP_STACK
> struct vm_struct *stack_vm_area;
> diff --git a/mm/oom_kill.c b/mm/oom_kill.c
> index 7ec38194f8e1..49d7df39b02d 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_reaper */
> 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 +658,48 @@ static int oom_reaper(void *unused)
> return 0;
> }
>
> -static void wake_oom_reaper(struct task_struct *tsk)
> +static void wake_oom_reaper(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 the OOM victim time to exit naturally before invoking the oom_reaping.
> + * The timers timeout is arbitrary... the longer it is, the longer the worst
> + * case scenario for the OOM can take. If it is too small, the oom_reaper can
> + * get in the way and release resources needed by the process exit path.
> + * e.g. The futex robust list can sit in Anon|Private memory that gets reaped
> + * before the exit path is able to wake the futex waiters.
> + */
> +#define OOM_REAPER_DELAY (2*HZ)
> +static void queue_oom_reaper(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, 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 +707,7 @@ 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_reaper(struct task_struct *tsk)
> {
> }
> #endif /* CONFIG_MMU */
> @@ -932,7 +958,7 @@ 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_reaper(victim);
>
> mmdrop(mm);
> put_task_struct(victim);
> @@ -968,7 +994,7 @@ 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_reaper(victim);
> task_unlock(victim);
> put_task_struct(victim);
> return;
> @@ -1067,7 +1093,7 @@ bool out_of_memory(struct oom_control *oc)
> */
> if (task_will_free_mem(current)) {
> mark_oom_victim(current);
> - wake_oom_reaper(current);
> + queue_oom_reaper(current);
> return true;
> }
>
> --
> 2.35.1
--
Michal Hocko
SUSE Labs
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