netdev - Re: [PATCH v2 net-next 06/14] netlink: hold nlk->cb_mutex longer in __netlink_dump

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Message-ID: <92ac2300-b1ba-44b0-98a0-c6ab084dfddd@I-love.SAKURA.ne.jp>
Date: Mon, 10 Jun 2024 22:21:08 +0900
From: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To: Eric Dumazet <edumazet@...gle.com>, Dmitry Vyukov <dvyukov@...gle.com>
Cc: Jiri Pirko <jiri@...nulli.us>, "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
        netdev@...r.kernel.org, Ido Schimmel <idosch@...dia.com>,
        Jiri Pirko <jiri@...dia.com>, eric.dumazet@...il.com
Subject: Re: [PATCH v2 net-next 06/14] netlink: hold nlk->cb_mutex longer in
 __netlink_dump_start()

On 2024/06/10 21:59, Eric Dumazet wrote:
> On Sun, Jun 9, 2024 at 10:29 AM Tetsuo Handa
> <penguin-kernel@...ove.sakura.ne.jp> wrote:
>>
>> On 2024/06/09 17:17, Tetsuo Handa wrote:
>>> Hello.
>>>
>>> While investigating hung task reports involving rtnl_mutex, I came to
>>> suspect that commit b5590270068c ("netlink: hold nlk->cb_mutex longer
>>> in __netlink_dump_start()") is buggy, for that commit made only
>>> mutex_lock(nlk->cb_mutex) side conditionally. Why don't we need to make
>>> mutex_unlock(nlk->cb_mutex) side conditionally?
>>>
>>
>> Sorry for the noise. That commit should be correct, for the caller
>> no longer calls mutex_unlock(nlk->cb_mutex).
>>
>> I'll try a debug printk() patch for linux-next.
> 
> I also have a lot of hung task reports as well, but in most reports
> the console is flooded
> before the crashes.

Yeah, printk() flooding is the cause of some of hung task reports.

I queued https://sourceforge.net/p/tomoyo/tomoyo.git/ci/c2bfadd666b5852974071df0588d7eb0f499b7b5/
for linux-next.git . You can try this patch to see what the owner of rtnl_mutex is doing.