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

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Message-Id: <201804080124.GHG87587.SVFOOQFLOHMJtF@I-love.SAKURA.ne.jp>
Date:   Sun, 8 Apr 2018 01:24:24 +0900
From:   Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To:     dvyukov@...gle.com, peterz@...radead.org
Cc:     mingo@...nel.org, akpm@...ux-foundation.org,
        paulmck@...ux.vnet.ibm.com, linux-kernel@...r.kernel.org,
        torvalds@...ux-foundation.org, msb@...omium.org,
        tglx@...utronix.de, vegard.nossum@...cle.com
Subject: Re: [PATCH v2] locking/hung_task: Show all hung tasks before panic

Dmitry Vyukov wrote:
> 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?

Maybe allow khungtaskd to call call_usermode_helper() to run arbitrary operations
instead of just calling panic()?

> 
> 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?
> 

It will be nice if syzbot testing is done with kdump configured, and the
result of automated scripting on vmcore (such as "foreach bt -s -l") is
available.