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

[Lance Yang <lance.yang@linux.dev>]

On 2025/9/28 11:19, Li,Rongqing wrote:
> 
> 
>> -----Original Message-----
>> From: Lance Yang <lance.yang@linux.dev>
>> Sent: 2025年9月27日 10:39
>> To: Li,Rongqing <lirongqing@baidu.com>
>> Cc: linux-doc@vger.kernel.org; linux-kernel@vger.kernel.org; arnd@arndb.de;
>> joel.granados@kernel.org; feng.tang@linux.alibaba.com; pauld@redhat.com;
>> kees@kernel.org; rostedt@goodmis.org; pawan.kumar.gupta@linux.intel.com;
>> akpm@linux-foundation.org; dave.hansen@linux.intel.com; mingo@kernel.org;
>> paulmck@kernel.org; corbet@lwn.net; mhiramat@kernel.org
>> 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@baidu.com>
>>>
>>> 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@baidu.com>
>>> ---
>>>    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@linux.dev>
>>
>>> +
>>>    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),
>