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

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Message-Id: <20250922145754.31890092257495f70db3909d@linux-foundation.org>
Date: Mon, 22 Sep 2025 14:57:54 -0700
From: Andrew Morton <akpm@...ux-foundation.org>
To: Lance Yang <lance.yang@...ux.dev>
Cc: Julian Sun <sunjunchao@...edance.com>, mhiramat@...nel.org,
 viro@...iv.linux.org.uk, brauner@...nel.org, jack@...e.cz,
 mingo@...hat.com, peterz@...radead.org, juri.lelli@...hat.com,
 vincent.guittot@...aro.org, dietmar.eggemann@....com, rostedt@...dmis.org,
 bsegall@...gle.com, mgorman@...e.de, vschneid@...hat.com,
 agruenba@...hat.com, hannes@...xchg.org, mhocko@...nel.org,
 roman.gushchin@...ux.dev, shakeel.butt@...ux.dev, muchun.song@...ux.dev,
 linux-kernel@...r.kernel.org, cgroups@...r.kernel.org,
 linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH 0/3] Suppress undesirable hung task warnings.

On Mon, 22 Sep 2025 19:38:21 +0800 Lance Yang <lance.yang@...ux.dev> wrote:

> On 2025/9/22 17:41, 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
> 
> Yep, I understand the goal is to suppress what can be a benign hung task
> warning during memcg teardown.
> 
> > 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.
> 
> However, I'm concerned that the PF_DONT_HUNG flag is a bit too powerful
> and might mask real, underlying hangs.

I think that's OK if the calling task is discriminating about it.  Just
set PF_DONT_HUNG (unpleasing name!) around those bits of code where
it's needed, clear it otherwise.

Julian, did you take a look at what a touch_hung_task_detector() would
involve?  It's a bit of an interface inconsistency - our various other
timeout detectors (softlockup, NMI, rcu) each have a touch_ function.