linux-kernel - Re: [PATCH 0/3] Suppress undesirable hung task warnings.

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Message-ID: <20250922132718.GB49638@noisy.programming.kicks-ass.net>
Date: Mon, 22 Sep 2025 15:27:18 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Julian Sun <sunjunchao@...edance.com>
Cc: cgroups@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org, viro@...iv.linux.org.uk,
	brauner@...nel.org, jack@...e.cz, mingo@...hat.com,
	juri.lelli@...hat.com, vincent.guittot@...aro.org,
	dietmar.eggemann@....com, rostedt@...dmis.org, bsegall@...gle.com,
	mgorman@...e.de, vschneid@...hat.com, akpm@...ux-foundation.org,
	lance.yang@...ux.dev, mhiramat@...nel.org, agruenba@...hat.com,
	hannes@...xchg.org, mhocko@...nel.org, roman.gushchin@...ux.dev,
	shakeel.butt@...ux.dev, muchun.song@...ux.dev
Subject: Re: [PATCH 0/3] Suppress undesirable hung task warnings.

On Mon, Sep 22, 2025 at 05:41:43PM +0800, Julian Sun wrote:
> As suggested by Andrew Morton in [1], we need a general mechanism 
> that allows the hung task detector to ignore unnecessary hung 
> tasks. This patch set implements this functionality.
> 
> Patch 1 introduces a PF_DONT_HUNG flag. The hung task detector will 
> ignores all tasks that have the PF_DONT_HUNG flag set.
> 
> Patch 2 introduces wait_event_no_hung() and wb_wait_for_completion_no_hung(), 
> which enable the hung task detector to ignore hung tasks caused by these
> wait events.
> 
> Patch 3 uses wb_wait_for_completion_no_hung() in the final phase of memcg 
> teardown to eliminate the hung task warning.
> 
> Julian Sun (3):
>   sched: Introduce a new flag PF_DONT_HUNG.
>   writeback: Introduce wb_wait_for_completion_no_hung().
>   memcg: Don't trigger hung task when memcg is releasing.

This is all quite terrible. I'm not at all sure why a task that is
genuinely not making progress and isn't killable should not be reported.