From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id C0979C4167E for ; Thu, 14 Apr 2022 15:45:17 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1358614AbiDNPmB (ORCPT ); Thu, 14 Apr 2022 11:42:01 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:33868 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1348537AbiDNOwj (ORCPT ); Thu, 14 Apr 2022 10:52:39 -0400 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 90B93C31CB for ; Thu, 14 Apr 2022 07:41:44 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1649947303; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding; bh=KbkJclTWBay2PEj54Brgd+xYZFlm7dVc8gZa/bypjmU=; b=cieRv6cJsGgpKDTt5w3djP6WkWdi8kOK/HJWsFQMjNF/JBOMVQc8yuxo20Ps++PrJwxnE6 5gxgDjluIi5IUrUQuoX9EgEgcVr4ujCSqtCBQDZxRxvLg4fsC5CscIPmWjVFB/slJ8Lyk6 XsuUsmnwdorxGHZzcbpayeU81OS61yc= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-524-bSWFm-5SPb64ZSQ6S0QV2w-1; Thu, 14 Apr 2022 10:41:40 -0400 X-MC-Unique: bSWFm-5SPb64ZSQ6S0QV2w-1 Received: from smtp.corp.redhat.com (int-mx10.intmail.prod.int.rdu2.redhat.com [10.11.54.10]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 3AD6018E5312; Thu, 14 Apr 2022 14:41:38 +0000 (UTC) Received: from localhost.localdomain.com (unknown [10.22.11.30]) by smtp.corp.redhat.com (Postfix) with ESMTP id 130444AE6FC; Thu, 14 Apr 2022 14:41:32 +0000 (UTC) From: Nico Pache To: linux-mm@kvack.org, linux-kernel@vger.kernel.org Cc: Rafael Aquini , Waiman Long , "Herton R . Krzesinski" , Juri Lelli , Vincent Guittot , Dietmar Eggemann , Steven Rostedt , Ben Segall , Mel Gorman , Daniel Bristot de Oliveira , David Rientjes , Michal Hocko , Andrea Arcangeli , Andrew Morton , Davidlohr Bueso , Peter Zijlstra , Ingo Molnar , Joel Savitz , Darren Hart , stable@kernel.org, Thomas Gleixner Subject: [PATCH v9] oom_kill.c: futex: Delay the OOM reaper to allow time for proper futex cleanup Date: Thu, 14 Apr 2022 10:40:42 -0400 Message-Id: <20220414144042.677008-1-npache@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 2.85 on 10.11.54.10 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 Cc: Waiman Long Cc: Herton R. Krzesinski Cc: Juri Lelli Cc: Vincent Guittot Cc: Dietmar Eggemann Cc: Steven Rostedt Cc: Ben Segall Cc: Mel Gorman Cc: Daniel Bristot de Oliveira Cc: David Rientjes Cc: Michal Hocko Cc: Andrea Arcangeli Cc: Andrew Morton Cc: Davidlohr Bueso Cc: Peter Zijlstra Cc: Ingo Molnar Cc: Joel Savitz Cc: Darren Hart Cc: stable@kernel.org Cc: Thomas Gleixner Suggested-by: Thomas Gleixner [ Based on a patch by Michal Hocko ] Co-developed-by: Joel Savitz Signed-off-by: Joel Savitz Signed-off-by: Nico Pache --- 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