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

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Message-ID: <20170822203632.GQ32112@worktop.programming.kicks-ass.net>
Date:   Tue, 22 Aug 2017 22:36:32 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Imran Khan <kimran@...eaurora.org>
Cc:     mingo@...nel.org, imrank140517@...il.com,
        "Luis R. Rodriguez" <mcgrof@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Shile Zhang <shile.zhang@...ia.com>,
        Matt Fleming <matt@...eblueprint.co.uk>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Vegard Nossum <vegard.nossum@...cle.com>,
        Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
        John Siddle <jsiddle@...hat.com>,
        open list <linux-kernel@...r.kernel.org>,
        "open list:PROC SYSCTL" <linux-fsdevel@...r.kernel.org>
Subject: Re: [PATCH] RFC: hung task: Check specific tasks for long
 uninterruptible sleep state

On Mon, Aug 21, 2017 at 03:55:53PM +0530, Imran Khan wrote:
> khungtask by default monitors either all tasks or no tasks at all
> for long unterruptible sleeps.
> For Android like environments this arrangement is not optimal because
> on one hand it may be permissible to have some background(bg) task
> in uninterruptible sleep state for long duration while on the other
> hand it may not be permissible to have some foreground(fg) task like
> surfaceflinger in uninterruptible sleep state for long duration.

How are you getting tasks in UNINTERRUPTIBLE state for a long time to
begin with? That's not a good thing, background or not.

> So it would be good to have some arrangement so that few specified tasks
> can be monitored by khungtaskd, on a need basis.
> This change introduces a sysctl option, /proc/sys/kernel/
> hung_task_check_selected, to enable monitoring of selected tasks using
> khungtask daemon. If this sysctl option is enabled then only the tasks
> specified in /proc/hung_task_monitor_list are monitored otherwise all
> tasks are monitored, just like the default case.

That's horrible. Why not a file in /proc/$PID/ that excludes it from
things?