linux-kernel - Re: [PATCH] hung_task: Skip hung task detection during core dump operations

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Message-Id: <20250814155825.851f99458a7be18069fc49aa@kernel.org>
Date: Thu, 14 Aug 2025 15:58:25 +0900
From: Masami Hiramatsu (Google) <mhiramat@...nel.org>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: "Nanji Parmar (he/him)" <nparmar@...estorage.com>, lance.yang@...ux.dev,
 mhiramat@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] hung_task: Skip hung task detection during core dump
 operations

On Wed, 13 Aug 2025 15:01:55 -0700
Andrew Morton <akpm@...ux-foundation.org> wrote:

> On Wed, 13 Aug 2025 11:30:36 -0700 "Nanji Parmar (he/him)" <nparmar@...estorage.com> wrote:
> 
> > Tasks involved in core dump operations can legitimately block for
> > extended periods, especially for large memory processes. The hung
> > task detector should skip tasks with PF_DUMPCORE (main dumping
> > thread) or PF_POSTCOREDUMP (other threads in the group) flags to
> > avoid false positive warnings.
> > 
> > This prevents incorrect hung task reports during legitimate core
> > dump generation that can take xx minutes for large processes.
> 
> It isn't pleasing to be putting coredump special cases into the core of
> the hung-task detector.  Perhaps the hung task detector should get an
> equivalent to touch_softlockup_watchdog().  I'm surprised it doesn't
> already have such a thing.  Maybe it does and I've forgotten where it is.

Hmm, maybe we can increase nvcsw/nivcsw to reset the hung task checker.
But usually this means the task does context switch while core-dump.

> 
> Please provide a full description of the problem, mainly the relevant
> dmesg output.  Please always provide this full description when
> addressing kernel issues, thanks.

+1, dmesg will show where (in kernel) we hit the hung_task during core dump.

Thanks,

-- 
Masami Hiramatsu (Google) <mhiramat@...nel.org>