linux-kernel - Re: [PATCH v2] locking/hung_task: Show all hung tasks before panic

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Date:   Sat, 7 Apr 2018 18:03:09 +0200
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
        Ingo Molnar <mingo@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Paul McKenney <paulmck@...ux.vnet.ibm.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Mandeep Singh Baines <msb@...omium.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Vegard Nossum <vegard.nossum@...cle.com>
Subject: Re: [PATCH v2] locking/hung_task: Show all hung tasks before panic

On Sat, Apr 7, 2018 at 5:39 PM, Peter Zijlstra <peterz@...radead.org> wrote:
> On Sat, Apr 07, 2018 at 09:31:19PM +0900, Tetsuo Handa wrote:
>> are for replacing debug_show_all_locks() in check_hung_task() for cases like
>> https://syzkaller.appspot.com/bug?id=26aa22915f5e3b7ca2cfca76a939f12c25d624db
>> because we are interested in only threads holding locks.
>>
>> SysRq-t is too much but SysRq-w is useless for killable/interruptible threads...
>
> Or use a script to process the sysrq-t output? I mean, we can add all
> sorts, but where does it end?

Good question.
We are talking about few dozen more stacks, right?

Not all kernel bugs are well reproducible, so it's not always possible
to go back and hit sysrq-t. And this come up in the context of syzbot,
which is an automated system. It reported a bunch of hangs and most of
them are real bugs, but not all of them are easily actionable.
Can it be a config or a command line argument, which will make syzbot
capture more useful context for each such hang?