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

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Message-Id: <201711082057.IDF56726.OMHOSFVFJtQOFL@I-love.SAKURA.ne.jp>
Date:   Wed, 8 Nov 2017 20:57:42 +0900
From:   Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To:     clingutla@...eaurora.org, kimran@...eaurora.org
Cc:     mingo@...nel.org, peterz@...radead.org, mcgrof@...nel.org,
        keescook@...omium.org, shile.zhang@...ia.com,
        matt@...eblueprint.co.uk, akpm@...ux-foundation.org,
        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

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?