linux-ext4 - Re: [syzbot] possible deadlock in start_this

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Message-ID: <03304bf8-d153-698f-0376-9e9a0ec1048e@I-love.SAKURA.ne.jp>
Date:   Fri, 15 Jul 2022 10:53:12 +0900
From:   Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To:     Shakeel Butt <shakeelb@...gle.com>
Cc:     Jan Kara <jack@...e.cz>, linux-mm@...ck.org, jack@...e.com,
        linux-ext4@...r.kernel.org, linux-kernel@...r.kernel.org,
        syzkaller-bugs@...glegroups.com, tytso@....edu,
        linux-fsdevel@...r.kernel.org
Subject: Re: [syzbot] possible deadlock in start_this_handle (3)

On 2022/07/15 10:39, Shakeel Butt wrote:
>> I think mem_cgroup_print_oom_meminfo() should use GFP_ATOMIC, for it will fall into
>> infinite loop if kmalloc(GFP_NOFS) under oom_lock reached __alloc_pages_may_oom() path.
> 
> I would prefer GFP_NOWAIT. This is printing info for memcg OOMs and if
> the system is low on memory then memcg OOMs has lower importance than
> the system state.

Since killing a process in some memcg likely helps solving global OOM state,
system OOM condition might not be reported when memory allocation by
mem_cgroup_print_oom_meminfo() caused system OOM condition.

Therefore, we don't need to discard output from memcg OOM condition.