linux-kernel - Re: [v2 PATCH 1/1] hung_task: Explicitly report I/O wait state in log output

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Message-ID: <p5xxorc3bzljkw6qgan2vxt4ar6wq4jaopoc7ysdjr7xzj2mes@uqfsz3x27k6o>
Date: Mon, 2 Feb 2026 20:24:42 -0500
From: Aaron Tomlin <atomlin@...mlin.com>
To: Petr Mladek <pmladek@...e.com>
Cc: akpm@...ux-foundation.org, lance.yang@...ux.dev, mhiramat@...nel.org, 
	gregkh@...uxfoundation.org, joel.granados@...nel.org, neelx@...e.com, sean@...e.io, 
	mproche@...il.com, chjohnst@...il.com, nick.lange@...il.com, 
	linux-kernel@...r.kernel.org
Subject: Re: [v2 PATCH 1/1] hung_task: Explicitly report I/O wait state in
 log output

On Mon, Feb 02, 2026 at 04:14:42PM +0100, Petr Mladek wrote:
> > Furthermore, as the task is
> > confirmed to be in a persistent TASK_UNINTERRUPTIBLE state, it cannot
> > modify its own in_iowait flag, rendering the read operation stable and
> > free from data races.
> 
> Strictly speaking, this is not true. IMHO, nothing prevents the task
> from waking up in parallel. Just the chance is small.
> 
> I would say that the information will be valid in 99.99% of situations
> because the message is printed only when the task has been stuck
> in the state for a long time. A possible mistake should be
> visible from the later printed backtrace.

Hi Petr,

Thank you for the review and the keen eye on the formatting.

You are entirely correct regarding the potential race; claiming the value
is strictly "stable" was imprecise. I have updated the commit message to
reflect that this is a diagnostic snapshot.

I also agree that we should not attempt to strictly prevent this race.

Theoretically, io_schedule_finish() could be called immediately after
"khungtaskd" checks the flag, rendering the output stale. However, strictly
preventing this would require blocking the waking task (e.g., within the
mutex unlock code path - see mutex_lock_io()) to inhibit the state change
during the scan. This seems entirely disproportionate for a "best effort"
diagnostic tool, especially given the probability of such a race is
negligible after a long hang, by default.

I have also adjusted the pr_err() format string to eliminate the potential
double space in the non-I/O case.

> Otherwise, it looks good.

Kind Regards,
-- 
Aaron Tomlin

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