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From: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
To: Michal Hocko <mhocko@kernel.org>
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>
Subject: Re: [PATCH] mm, oom: Introduce time limit for dump_tasks duration.
Date: Thu, 6 Sep 2018 20:40:34 +0900	[thread overview]
Message-ID: <1611e45d-235e-67e9-26e3-d0228255fa2f@i-love.sakura.ne.jp> (raw)
In-Reply-To: <20180906112306.GO14951@dhcp22.suse.cz>

On 2018/09/06 20:23, Michal Hocko wrote:
> 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).

I know /proc/sys/vm/oom_dump_tasks . Showing some entries while not always
printing all entries might be helpful. For example, allow
/proc/sys/vm/oom_dump_tasks > 1 and use it as timeout in seconds.

  reply	other threads:[~2018-09-06 12:24 UTC|newest]

Thread overview: 25+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <0000000000004a6b700575178b5a@google.com>
     [not found] ` <CACT4Y+aPRGUqAdJCMDWM=Zcy8ZQcHyrsB1ZuWS4VB_+wvLfeaQ@mail.gmail.com>
2018-09-05 10:53   ` INFO: task hung in ext4_da_get_block_prep Tetsuo Handa
2018-09-05 11:06     ` Dmitry Vyukov
2018-09-06  5:53       ` Tetsuo Handa
2018-09-06  9:54         ` Dmitry Vyukov
2018-09-06 10:58           ` [PATCH] mm, oom: Introduce time limit for dump_tasks duration Tetsuo Handa
2018-09-06 11:07             ` Dmitry Vyukov
2018-09-06 11:25               ` Tetsuo Handa
2018-09-06 11:23             ` Michal Hocko
2018-09-06 11:40               ` Tetsuo Handa [this message]
2018-09-06 11:53                 ` Michal Hocko
2018-09-06 12:08                   ` Dmitry Vyukov
2018-09-06 12:16                     ` Michal Hocko
2018-09-11 16:37                       ` Oleg Nesterov
2018-09-12 16:45                         ` Oleg Nesterov
2018-09-06 13:45                   ` Tetsuo Handa
2018-09-06 14:39                     ` Michal Hocko
2018-09-06 20:58                       ` Tetsuo Handa
2018-09-07  8:27                         ` Michal Hocko
2018-09-07  9:36                           ` Dmitry Vyukov
2018-09-07 10:49                             ` Tetsuo Handa
2018-09-07 11:08                             ` Michal Hocko
2018-09-08 14:00                               ` Dmitry Vyukov
2018-09-10 14:36                                 ` Dmitry Vyukov
2018-09-07 10:20                           ` Tetsuo Handa
2019-03-03 11:33 ` INFO: task hung in ext4_da_get_block_prep syzbot

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