Re: [外部邮件] Re: [PATCH] hung_task: Panic after fixed number of hung tasks

[Lance Yang]

On 2025/9/28 11:19, Li,Rongqing wrote:
> > -----Original Message-----
> > From: Lance Yang <lance.yang@xxxxxxxxx>
> > Sent: 2025年9月27日 10:39
> > To: Li,Rongqing <lirongqing@xxxxxxxxx>
> > Cc: linux-doc@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; arnd@xxxxxxxx;
> > joel.granados@xxxxxxxxxx; feng.tang@xxxxxxxxxxxxxxxxx; pauld@xxxxxxxxxx;
> > kees@xxxxxxxxxx; rostedt@xxxxxxxxxxx; pawan.kumar.gupta@xxxxxxxxxxxxxxx;
> > akpm@xxxxxxxxxxxxxxxxxxxx; dave.hansen@xxxxxxxxxxxxxxx; mingo@xxxxxxxxxx;
> > paulmck@xxxxxxxxxx; corbet@xxxxxxx; mhiramat@xxxxxxxxxx
> > Subject: [外部邮件] Re: [PATCH] hung_task: Panic after fixed number of hung
> > tasks
> >
> >
> >
> > On 2025/9/25 14:06, lirongqing wrote:
> > > From: Li RongQing <lirongqing@xxxxxxxxx>
> > >
> > > Currently, when hung_task_panic is enabled, kernel will panic
> > > immediately upon detecting the first hung task. However, some hung
> > > tasks are transient and the system can recover fully, while others are
> > > unrecoverable and trigger consecutive hung task reports, and a panic is
> > expected.
> > > This commit adds a new sysctl parameter hung_task_count_to_panic to
> > > allows specifying the number of consecutive hung tasks that must be
> > > detected before triggering a kernel panic. This provides finer control
> > > for environments where transient hangs maybe happen but persistent
> > > hangs should still be fatal.
> > >
> > > Signed-off-by: Li RongQing <lirongqing@xxxxxxxxx>
> > > ---
> > >    Documentation/admin-guide/sysctl/kernel.rst |  6 ++++++
> > >    kernel/hung_task.c                          | 14 +++++++++++++-
> > >    2 files changed, 19 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/Documentation/admin-guide/sysctl/kernel.rst
> > > b/Documentation/admin-guide/sysctl/kernel.rst
> > > index 8b49eab..4240e7b 100644
> > > --- a/Documentation/admin-guide/sysctl/kernel.rst
> > > +++ b/Documentation/admin-guide/sysctl/kernel.rst
> > > @@ -405,6 +405,12 @@ This file shows up if
> > ``CONFIG_DETECT_HUNG_TASK`` is enabled.
> > >    1 Panic immediately.
> > >    = =================================================
> > >
> > > +hung_task_count_to_panic
> > > +=====================
> > > +
> > > +When set to a non-zero value, after the number of consecutive hung
> > > +task occur, the kernel will triggers a panic
> >
> > Hmm... the documentation here seems a bit misleading.
> >
> > hung_task_panic=1 will always cause an immediate panic, regardless of the
> > hung_task_count_to_panic setting, right?
> >
> > Perhaps something like this would be more accurate?
> >
> > ```
> > hung_task_count_to_panic
> > ========================
> >
> > When set to a non-zero value, a kernel panic will be triggered if the number of
> > detected hung tasks reaches this value.
> >
> > Note that setting hung_task_panic=1 will still cause an immediate panic on the
> > first hung task, overriding this setting.
> > ```
> >
> > >    hung_task_check_count
> > >    =====================
> > > diff --git a/kernel/hung_task.c b/kernel/hung_task.c index
> > > 8708a12..87a6421 100644
> > > --- a/kernel/hung_task.c
> > > +++ b/kernel/hung_task.c
> > > @@ -83,6 +83,8 @@ static unsigned int __read_mostly
> > sysctl_hung_task_all_cpu_backtrace;
> > >    static unsigned int __read_mostly sysctl_hung_task_panic =
> > >    	IS_ENABLED(CONFIG_BOOTPARAM_HUNG_TASK_PANIC);
> > >
> > > +static unsigned int __read_mostly sysctl_hung_task_count_to_panic;
> >
> > Nit: while static variables are guaranteed to be zero-initialized, it's a good
> > practice and clearer for readers to initialize them explicitly.
> >
> > static unsigned int __read_mostly sysctl_hung_task_count_to_panic = 0;
>
> ./scripts/checkpatch.pl reports error when initialise statics to 0, so I will keep it uninitialized
>
> ERROR: do not initialise statics to 0
> #51: FILE: kernel/hung_task.c:86:
> +static unsigned int __read_mostly sysctl_hung_task_count_to_panic = 0;

Ah, good spot! Let’s leave it as is ;)

Cheers,
Lance

> thanks
>
> -Li
>
> > Otherwise, this patch looks good to me!
> > Acked-by: Lance Yang <lance.yang@xxxxxxxxx>
> >
> > > +
> > >    static int
> > >    hung_task_panic(struct notifier_block *this, unsigned long event, void *ptr)
> > >    {
> > > @@ -219,7 +221,9 @@ static void check_hung_task(struct task_struct *t,
> > > unsigned long timeout)
> > >
> > >    	trace_sched_process_hang(t);
> > >
> > > -	if (sysctl_hung_task_panic) {
> > > +	if (sysctl_hung_task_panic ||
> > > +	    (sysctl_hung_task_count_to_panic &&
> > > +	     (sysctl_hung_task_detect_count >=
> > > +sysctl_hung_task_count_to_panic))) {
> > >    		console_verbose();
> > >    		hung_task_show_lock = true;
> > >    		hung_task_call_panic = true;
> > > @@ -388,6 +392,14 @@ static const struct ctl_table hung_task_sysctls[] = {
> > >    		.extra2		= SYSCTL_ONE,
> > >    	},
> > >    	{
> > > +		.procname	= "hung_task_count_to_panic",
> > > +		.data		= &sysctl_hung_task_count_to_panic,
> > > +		.maxlen		= sizeof(int),
> > > +		.mode		= 0644,
> > > +		.proc_handler	= proc_dointvec_minmax,
> > > +		.extra1		= SYSCTL_ZERO,
> > > +	},
> > > +	{
> > >    		.procname	= "hung_task_check_count",
> > >    		.data		= &sysctl_hung_task_check_count,
> > >    		.maxlen		= sizeof(int),