linux-kernel - Re: [????] Re: [PATCH][v3] hung_task: Panic after fixed number of hung tasks

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Message-ID: <aO5Ldv4U8QSGgfog@pathway.suse.cz>
Date: Tue, 14 Oct 2025 15:09:10 +0200
From: Petr Mladek <pmladek@...e.com>
To: "Li,Rongqing" <lirongqing@...du.com>
Cc: Lance Yang <lance.yang@...ux.dev>,
	"wireguard@...ts.zx2c4.com" <wireguard@...ts.zx2c4.com>,
	"linux-arm-kernel@...ts.infradead.org" <linux-arm-kernel@...ts.infradead.org>,
	"Liam R . Howlett" <Liam.Howlett@...cle.com>,
	"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
	David Hildenbrand <david@...hat.com>,
	Randy Dunlap <rdunlap@...radead.org>,
	Stanislav Fomichev <sdf@...ichev.me>,
	"linux-aspeed@...ts.ozlabs.org" <linux-aspeed@...ts.ozlabs.org>,
	Andrew Jeffery <andrew@...econstruct.com.au>,
	Joel Stanley <joel@....id.au>, Russell King <linux@...linux.org.uk>,
	Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
	Shuah Khan <shuah@...nel.org>, Steven Rostedt <rostedt@...dmis.org>,
	Jonathan Corbet <corbet@....net>,
	Joel Granados <joel.granados@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
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	Masami Hiramatsu <mhiramat@...nel.org>,
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	"Jason A . Donenfeld" <Jason@...c4.com>
Subject: Re: [????] Re: [PATCH][v3] hung_task: Panic after fixed number of
 hung tasks

On Tue 2025-10-14 10:49:53, Li,Rongqing wrote:
> 
> > On Tue 2025-10-14 13:23:58, Lance Yang wrote:
> > > Thanks for the patch!
> > >
> > > I noticed the implementation panics only when N tasks are detected
> > > within a single scan, because total_hung_task is reset for each
> > > check_hung_uninterruptible_tasks() run.
> > 
> > Great catch!
> > 
> > Does it make sense?
> > Is is the intended behavior, please?
> > 
> 
> Yes, this is intended behavior
> 
> > > So some suggestions to align the documentation with the code's
> > > behavior below :)
> > 
> > > On 2025/10/12 19:50, lirongqing wrote:
> > > > From: Li RongQing <lirongqing@...du.com>
> > > >
> > > > Currently, when 'hung_task_panic' is enabled, the kernel panics
> > > > immediately upon detecting the first hung task. However, some hung
> > > > tasks are transient and the system can recover, while others are
> > > > persistent and may accumulate progressively.
> > 
> > My understanding is that this patch wanted to do:
> > 
> >    + report even temporary stalls
> >    + panic only when the stall was much longer and likely persistent
> > 
> > Which might make some sense. But the code does something else.
> > 
> 
> A single task hanging for an extended period may not be a critical
> issue, as users might still log into the system to investigate.
> However, if multiple tasks hang simultaneously-such as in cases
> of I/O hangs caused by disk failures-it could prevent users from
> logging in and become a serious problem, and a panic is expected.

I see. This another approach and it makes sense as well.
An this is much more clear description than the original text.

I would also update the subject to something like:

    hung_task: Panic when there are more than N hung tasks at the same time



That said, I think that both approaches make sense.

Your approach would trigger the panic when many processes are stuck.
Note that it still might be a transient state. But I agree that
the more stuck processes exist the more serious the problem
likely is for the heath of the system.

My approach would trigger panic when a single process hangs
for a long time. It will trigger more likely only when the problem
is persistent. The seriousness depends on which particular process
get stuck.

I am fine with your approach. Just please, make more clear that
the number means the number of hung tasks at the same time.
And mention the problems to login, ...

Best Regards,
Petr