linux-kernel - Re: [RFC] hung task: check specific tasks for long uninterruptible sleep state

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Message-Id: <20171108154429.909e12c5f7141cde37416469@linux-foundation.org>
Date:   Wed, 8 Nov 2017 15:44:29 -0800
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
Cc:     clingutla@...eaurora.org, kimran@...eaurora.org, mingo@...nel.org,
        peterz@...radead.org, mcgrof@...nel.org, keescook@...omium.org,
        shile.zhang@...ia.com, matt@...eblueprint.co.uk,
        vegard.nossum@...cle.com, jsiddle@...hat.com,
        linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [RFC] hung task: check specific tasks for long uninterruptible
 sleep state

On Wed, 8 Nov 2017 20:57:42 +0900 Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp> wrote:

> Lingutla Chandrasekhar wrote:
> > Some tasks may intentionally moves to uninterruptable sleep state,
> > which shouldn't leads to khungtask panics, as those are recoverable
> > hungs. So to avoid false hung reports, add an option to select tasks
> > to be monitored and report/panic them only.
> 
> What are backtraces of such tasks? Please point the locations in the code.
> 
> If they are absolutely recoverable, why can't we let themselves declare that
> "I'm intentionally in uninterruptible state. But there is no dependency that
> prevents me from recovering. So, please ignore me." using per "struct
> task_struct" flags rather than introducing userspace controlled interface?

Yes.  Please tell us much much much more about the use case and
scenarios which inspired this change.