linux-kernel - Re: + mm-memcontrol-fix-potential-oom_lock-recursion-deadlock.patch added to mm-unstable branch

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Date:   Tue, 26 Jul 2022 11:50:29 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
Cc:     Michal Hocko <mhocko@...e.com>, mm-commits@...r.kernel.org,
        syzbot+2d2aeadc6ce1e1f11d45@...kaller.appspotmail.com,
        shakeelb@...gle.com, roman.gushchin@...ux.dev, hannes@...xchg.org,
        linux-kernel@...r.kernel.org
Subject: Re: + mm-memcontrol-fix-potential-oom_lock-recursion-deadlock.patch
 added to mm-unstable branch

On Tue, 26 Jul 2022 20:31:17 +0900 Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp> wrote:

> syzbot is reporting GFP_KERNEL allocation with oom_lock held when
> reporting memcg OOM [1]. If this allocation triggers the global OOM
> situation then the system can livelock because the GFP_KERNEL allocation
> with oom_lock held cannot trigger the global OOM killer because
> __alloc_pages_may_oom() fails to hold oom_lock.
> 
> Fix this problem by removing the allocation from memory_stat_format()
> completely, and pass static buffer when calling from memcg OOM path.
> 
> Note that the caller holding filesystem lock was the trigger for syzbot
> to report this locking dependency. Doing GFP_KERNEL allocation with
> filesystem lock held can deadlock the system even without involving OOM
> situation.

I used the above as the new changelog text.