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

[Masami Hiramatsu (Google) <mhiramat@kernel.org>]

On Wed, 28 Jan 2026 15:45:16 -0500
Aaron Tomlin <atomlin@atomlin.com> wrote:

> Currently, the hung task reporting mechanism indiscriminately labels all
> TASK_UNINTERRUPTIBLE (D) tasks as "blocked", irrespective of whether they
> are awaiting I/O completion or kernel locking primitives. This ambiguity
> compels system administrators to manually inspect stack traces to discern
> whether the delay stems from an I/O wait (typically indicative of
> hardware or filesystem anomalies) or software contention. Such detailed
> analysis is not always immediately accessible to system administrators
> or support engineers.
> 
> To address this, this patch utilises the existing in_iowait field within
> struct task_struct to augment the failure report. If the task is blocked
> due to I/O (e.g., via io_schedule_prepare()), the log message is updated
> to explicitly state "blocked in I/O wait".
> 
> Examples:
>         - Standard Block: "INFO: task bash:123 blocked for more than 120
>           seconds".
> 
>         - I/O Block: "INFO: task dd:456 blocked in I/O wait for more than
>           120 seconds".
> 
> Accessing in_iowait is safe in this context. The detector holds
> rcu_read_lock() within check_hung_uninterruptible_tasks(), ensuring the
> task structure remains valid in memory. 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.
> 
> Signed-off-by: Aaron Tomlin <atomlin@atomlin.com>

Looks good to me.

Acked-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>

Thanks,


> ---
>  kernel/hung_task.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/kernel/hung_task.c b/kernel/hung_task.c
> index 350093de0535..abfbb5d9eeee 100644
> --- a/kernel/hung_task.c
> +++ b/kernel/hung_task.c
> @@ -250,8 +250,9 @@ static void hung_task_info(struct task_struct *t, unsigned long timeout,
>  	if (sysctl_hung_task_warnings || hung_task_call_panic) {
>  		if (sysctl_hung_task_warnings > 0)
>  			sysctl_hung_task_warnings--;
> -		pr_err("INFO: task %s:%d blocked for more than %ld seconds.\n",
> -		       t->comm, t->pid, (jiffies - t->last_switch_time) / HZ);
> +		pr_err("INFO: task %s:%d blocked %s for more than %ld seconds.\n",
> +		       t->comm, t->pid, t->in_iowait ? "in I/O wait" : "",
> +		       (jiffies - t->last_switch_time) / HZ);
>  		pr_err("      %s %s %.*s\n",
>  			print_tainted(), init_utsname()->release,
>  			(int)strcspn(init_utsname()->version, " "),
> -- 
> 2.51.0
> 


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