linux-kernel - Re: [PATCH v3 1/2] hung_task: Introduce helper for hung task warning

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Message-ID: <aUJ6O9cYXd_9ANF1@pathway.suse.cz>
Date: Wed, 17 Dec 2025 10:39:07 +0100
From: Petr Mladek <pmladek@...e.com>
To: Aaron Tomlin <atomlin@...mlin.com>
Cc: akpm@...ux-foundation.org, lance.yang@...ux.dev, mhiramat@...nel.org,
	gregkh@...uxfoundation.org, sean@...e.io,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 1/2] hung_task: Introduce helper for hung task warning

On Mon 2025-12-15 22:00:35, Aaron Tomlin wrote:
> Consolidate the multi-line console output block for reporting a hung
> task into a new helper function, hung_task_diagnostics(). This improves
> readability in the main check_hung_task() loop and makes the diagnostic
> output structure easier to maintain and update in the future.
> 
> Signed-off-by: Aaron Tomlin <atomlin@...mlin.com>
> ---
>  kernel/hung_task.c | 37 +++++++++++++++++++++++++++----------
>  1 file changed, 27 insertions(+), 10 deletions(-)
> 
> diff --git a/kernel/hung_task.c b/kernel/hung_task.c
> index d2254c91450b..5902573200c0 100644
> --- a/kernel/hung_task.c
> +++ b/kernel/hung_task.c
> @@ -223,6 +223,32 @@ static inline void debug_show_blocker(struct task_struct *task, unsigned long ti
>  }
>  #endif
>  
> +/**
> + * hung_task_diagnostics - Print structured diagnostic info for a hung task.
> + * @t: Pointer to the detected hung task.
> + *
> + * This function consolidates the printing of core diagnostic information
> + * for a task found to be blocked.
> + */
> +static inline void hung_task_diagnostics(struct task_struct *t)
> +{
> +	unsigned long blocked_secs = (jiffies - t->last_switch_time) / HZ;

It makes sense to make the computation separately.

> +	const char *coredump_msg = "      Blocked by coredump.";

Honestly, I do not see any advantage in storing the string into a
variable and passing it via %s. It does not help with readability
because the reader has to lookup the variable definition. And it
is less effective code (not a big deal but...).

Instead, I would add "\n". It will allow to show the message
immediately on consoles. Without the trailing "\n", the message
is not finalized because it might still get extended by pr_cont().

> +	const char *disable_msg =
> +		"\"echo 0 > /proc/sys/kernel/hung_task_timeout_secs\""
> +		" disables this message.";

Same here. I would avoid the %s and add the trailing '\n'.

Also the message should be on a single line. It makes it easier
to find it via "git grep". ./scripts/checkpatch.pl even complain
about it:

WARNING: quoted string split across lines
#37: FILE: kernel/hung_task.c:239:
+		"\"echo 0 > /proc/sys/kernel/hung_task_timeout_secs\""
+		" disables this message.";


> +	pr_err("INFO: task %s:%d blocked for more than %ld seconds.\n",
> +	       t->comm, t->pid, blocked_secs);
> +	pr_err("      %s %s %.*s\n",
> +	       print_tainted(), init_utsname()->release,
> +	       (int)strcspn(init_utsname()->version, " "),
> +	       init_utsname()->version);
> +	if (t->flags & PF_POSTCOREDUMP)
> +		pr_err("%s\n", coredump_msg);
> +	pr_err("%s\n", disable_msg);
> +}

Otherwise, I like the change.

Best Regards,
Petr