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

[Feng Tang]

On Sun, Nov 16, 2025 at 09:22:43PM +0800, Lance Yang wrote:
> > > 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?

Andrew has taken the patchset to -mm tree. 

Andrew, which way do you prefer? I send a v3 patch for hung-task or you
pickup the fixup patch and squash it into the orginal 0002 patch?

Anyway, I make a squshed version v3 patch below.

Thanks,
Feng

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