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Date: Thu, 6 Sep 2018 13:23:06 +0200
From: Michal Hocko <mhocko@kernel.org>
Subject: Re: [PATCH] mm, oom: Introduce time limit for dump_tasks duration.
Message-ID: <20180906112306.GO14951@dhcp22.suse.cz>
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To: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
Cc: Dmitry Vyukov <dvyukov@google.com>, Andrew Morton <akpm@linux-foundation.org>, David Rientjes <rientjes@google.com>, syzbot <syzbot+f0fc7f62e88b1de99af3@syzkaller.appspotmail.com>, 'Dmitry Vyukov' via syzkaller-upstream-moderation <syzkaller-upstream-moderation@googlegroups.com>, linux-mm <linux-mm@kvack.org>

On Thu 06-09-18 19:58:25, Tetsuo Handa wrote:
[...]
> >From 18876f287dd69a7c33f65c91cfcda3564233f55e Mon Sep 17 00:00:00 2001
> From: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
> Date: Thu, 6 Sep 2018 19:53:18 +0900
> Subject: [PATCH] mm, oom: Introduce time limit for dump_tasks duration.
> 
> Since printk() is slow, printing one line takes nearly 0.01 second.
> As a result, syzbot is stalling for 52 seconds trying to dump 5600
> tasks at for_each_process() under RCU. Since such situation is almost
> inflight fork bomb attack (the OOM killer will print similar tasks for
> so many times), it makes little sense to print all candidate tasks.
> Thus, this patch introduces 3 seconds limit for printing.
> 
> Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
> Cc: Dmitry Vyukov <dvyukov@google.com>

You really love timeout based solutions with randomly chosen timeouts,
don't you. This is just ugly as hell. We already have means to disable
tasks dumping (see /proc/sys/vm/oom_dump_tasks).
-- 
Michal Hocko
SUSE Labs