Re: [PATCH v2 2/4] hung_task: Add hung_task_sys_info sysctl to dump sys info on task-hung

[Lance Yang]

On 2025/11/16 17:11, Feng Tang wrote:
> On Sun, Nov 16, 2025 at 03:58:32PM +0800, Lance Yang wrote:
> > On 2025/11/13 19:10, Feng Tang wrote:
> > > When task-hung happens, developers may need different kinds of system
> > > information (call-stacks, memory info, locks, etc.) to help debugging.
> > >
> > > Add 'hung_task_sys_info' sysctl knob to take human readable string like
> > > "tasks,mem,timers,locks,ftrace,...", and when task-hung happens, all
> > > requested information will be dumped. (refer kernel/sys_info.c for more
> > > details).
> > >
> > > Meanwhile, the newly introduced sys_info() call is used to unify some
> > > existing info-dumping knobs.
> > >
> > > Suggested-by: Petr Mladek <pmladek@xxxxxxxx>
> > > Signed-off-by: Feng Tang <feng.tang@xxxxxxxxxxxxxxxxx>
> > > ---
> > >    Documentation/admin-guide/sysctl/kernel.rst |  5 ++
> > >    kernel/hung_task.c                          | 62 +++++++++++++--------
> > >    2 files changed, 43 insertions(+), 24 deletions(-)
> > >    	 * Ok, the task did not get scheduled for more than 2 minutes,
> > >    	 * complain:
> > >    	 */
> > > -	if (sysctl_hung_task_warnings || hung_task_call_panic) {
> > > +	if (sysctl_hung_task_warnings) {
> >
> > It seems like the behavior changes when sysctl_hung_task_warnings is
> > 0 but a panic is about to be triggered ...
> >
> > Looking at the history:
> >
> > 1) Commit ("hung_task: ignore hung_task_warnings when hung_task_panic
> > is enabled")[1] ensured that hung task information is always dumped
> > when a panic is configured, even if the warning counter is exhausted.
> >
> > 2) Later, commit ("hung_task: panic when there are more than N hung
> > tasks at the same time")[2] refined the logic to trigger a panic based
> > on the number of hung tasks found in a single scan.
> >
> > To stay consistent with the established behavior, I think we should
> > continue to dump the information for hung tasks as long as
> > sysctl_hung_task_panic is enabled :)
> >
> > [1] https://lore.kernel.org/all/20240613033159.3446265-1-leonylgao@xxxxxxxxx
> > [2] https://lore.kernel.org/all/20251015063615.2632-1-lirongqing@xxxxxxxxx
> > [...]
>
> Aha, Petr asked similar question during his review. Thanks for the catch!
>
> How about following fixup patch to restore that part of logic?
>
> Thanks,
> Feng
>
> ---
> diff --git a/kernel/hung_task.c b/kernel/hung_task.c
> index 5b3a7785d3a2..d2254c91450b 100644
> --- a/kernel/hung_task.c
> +++ b/kernel/hung_task.c
> @@ -223,8 +223,11 @@ static inline void debug_show_blocker(struct task_struct *task, unsigned long ti
>   }
>   #endif
>   
> -static void check_hung_task(struct task_struct *t, unsigned long timeout)
> +static void check_hung_task(struct task_struct *t, unsigned long timeout,
> +		unsigned long prev_detect_count)
>   {
> +	unsigned long total_hung_task;
> +
>   	if (!task_is_hung(t, timeout))
>   		return;
>   
> @@ -234,13 +237,19 @@ static void check_hung_task(struct task_struct *t, unsigned long timeout)
>   	 */
>   	sysctl_hung_task_detect_count++;
>   
> +	total_hung_task = sysctl_hung_task_detect_count - prev_detect_count;
>   	trace_sched_process_hang(t);
>   
> +	if (sysctl_hung_task_panic && total_hung_task >= sysctl_hung_task_panic) {
> +		console_verbose();
> +		hung_task_call_panic = true;
> +	}
> +
>   	/*
>   	 * Ok, the task did not get scheduled for more than 2 minutes,
>   	 * complain:
>   	 */
> -	if (sysctl_hung_task_warnings) {
> +	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",
> @@ -295,7 +304,6 @@ static void check_hung_uninterruptible_tasks(unsigned long timeout)
>   {
>   	int max_count = sysctl_hung_task_check_count;
>   	unsigned long last_break = jiffies;
> -	unsigned long total_hung_task;
>   	struct task_struct *g, *t;
>   	unsigned long prev_detect_count = sysctl_hung_task_detect_count;
>   	int need_warning = sysctl_hung_task_warnings;
> @@ -320,20 +328,14 @@ static void check_hung_uninterruptible_tasks(unsigned long timeout)
>   			last_break = jiffies;
>   		}
>   
> -		check_hung_task(t, timeout);
> +		check_hung_task(t, timeout, prev_detect_count);
>   	}
>    unlock:
>   	rcu_read_unlock();
>   
> -	total_hung_task = sysctl_hung_task_detect_count - prev_detect_count;
> -	if (!total_hung_task)
> +	if (!(sysctl_hung_task_detect_count - prev_detect_count))
>   		return;
>   
> -	if (sysctl_hung_task_panic && total_hung_task >= sysctl_hung_task_panic) {
> -		console_verbose();
> -		hung_task_call_panic = true;
> -	}
> -
>   	if (need_warning || hung_task_call_panic) {
>   		si_mask |= SYS_INFO_LOCKS;

Looks good to me now! I assume v3 would be expected, can you
post a new version?

Cheers,
Lance