From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-it0-f69.google.com (mail-it0-f69.google.com [209.85.214.69]) by kanga.kvack.org (Postfix) with ESMTP id 54A766B0033 for ; Thu, 7 Dec 2017 16:55:11 -0500 (EST) Received: by mail-it0-f69.google.com with SMTP id b11so467268itj.0 for ; Thu, 07 Dec 2017 13:55:11 -0800 (PST) Received: from mail-sor-f65.google.com (mail-sor-f65.google.com. [209.85.220.65]) by mx.google.com with SMTPS id t134sor77523itf.23.2017.12.07.13.55.09 for (Google Transport Security); Thu, 07 Dec 2017 13:55:09 -0800 (PST) Date: Thu, 7 Dec 2017 13:55:07 -0800 (PST) From: David Rientjes Subject: Re: Multiple oom_reaper BUGs: unmap_page_range racing with exit_mmap In-Reply-To: <20171207163003.GM20234@dhcp22.suse.cz> Message-ID: References: <20171207113548.GG20234@dhcp22.suse.cz> <201712080044.BID56711.FFVOLMStJOQHOF@I-love.SAKURA.ne.jp> <20171207163003.GM20234@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-linux-mm@kvack.org List-ID: To: Michal Hocko Cc: Tetsuo Handa , akpm@linux-foundation.org, aarcange@redhat.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org On Thu, 7 Dec 2017, Michal Hocko wrote: > yes. I will fold the following in if this turned out to really address > David's issue. But I suspect this will be the case considering the NULL > pmd in the report which would suggest racing with free_pgtable... > I'm backporting and testing the following patch against Linus's tree. To clarify an earlier point, we don't actually have any change from upstream code that allows for free_pgtables() before the set_bit(MMF_OOM_SKIP);down_write();up_write() cycle. diff --git a/include/linux/oom.h b/include/linux/oom.h --- a/include/linux/oom.h +++ b/include/linux/oom.h @@ -66,6 +66,15 @@ static inline bool tsk_is_oom_victim(struct task_struct * tsk) return tsk->signal->oom_mm; } +/* + * Use this helper if tsk->mm != mm and the victim mm needs a special + * handling. This is guaranteed to stay true after once set. + */ +static inline bool mm_is_oom_victim(struct mm_struct *mm) +{ + return test_bit(MMF_OOM_VICTIM, &mm->flags); +} + /* * Checks whether a page fault on the given mm is still reliable. * This is no longer true if the oom reaper started to reap the diff --git a/include/linux/sched/coredump.h b/include/linux/sched/coredump.h --- a/include/linux/sched/coredump.h +++ b/include/linux/sched/coredump.h @@ -71,6 +71,7 @@ static inline int get_dumpable(struct mm_struct *mm) #define MMF_HUGE_ZERO_PAGE 23 /* mm has ever used the global huge zero page */ #define MMF_DISABLE_THP 24 /* disable THP for all VMAs */ #define MMF_DISABLE_THP_MASK (1 << MMF_DISABLE_THP) +#define MMF_OOM_VICTIM 25 /* mm is the oom victim */ #define MMF_INIT_MASK (MMF_DUMPABLE_MASK | MMF_DUMP_FILTER_MASK |\ MMF_DISABLE_THP_MASK) diff --git a/mm/mmap.c b/mm/mmap.c --- a/mm/mmap.c +++ b/mm/mmap.c @@ -3019,20 +3019,20 @@ void exit_mmap(struct mm_struct *mm) /* Use -1 here to ensure all VMAs in the mm are unmapped */ unmap_vmas(&tlb, vma, 0, -1); - set_bit(MMF_OOM_SKIP, &mm->flags); - if (unlikely(tsk_is_oom_victim(current))) { + if (unlikely(mm_is_oom_victim(mm))) { /* * Wait for oom_reap_task() to stop working on this * mm. Because MMF_OOM_SKIP is already set before * calling down_read(), oom_reap_task() will not run * on this "mm" post up_write(). * - * tsk_is_oom_victim() cannot be set from under us + * mm_is_oom_victim() cannot be set from under us * either because current->mm is already set to NULL * under task_lock before calling mmput and oom_mm is * set not NULL by the OOM killer only if current->mm * is found not NULL while holding the task_lock. */ + set_bit(MMF_OOM_SKIP, &mm->flags); down_write(&mm->mmap_sem); up_write(&mm->mmap_sem); } diff --git a/mm/oom_kill.c b/mm/oom_kill.c --- a/mm/oom_kill.c +++ b/mm/oom_kill.c @@ -683,8 +683,10 @@ static void mark_oom_victim(struct task_struct *tsk) return; /* oom_mm is bound to the signal struct life time. */ - if (!cmpxchg(&tsk->signal->oom_mm, NULL, mm)) + if (!cmpxchg(&tsk->signal->oom_mm, NULL, mm)) { mmgrab(tsk->signal->oom_mm); + set_bit(MMF_OOM_VICTIM, &mm->flags); + } /* * Make sure that the task is woken up from uninterruptible sleep -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org