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

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Message-ID: <096168a6-8687-4dae-a774-0741d3e5a891@linux.dev>
Date: Tue, 14 Oct 2025 19:40:58 +0800
From: Lance Yang <lance.yang@...ux.dev>
To: "Li,Rongqing" <lirongqing@...du.com>, Petr Mladek <pmladek@...e.com>
Cc: "wireguard@...ts.zx2c4.com" <wireguard@...ts.zx2c4.com>,
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 <linux-arm-kernel@...ts.infradead.org>,
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 David Hildenbrand <david@...hat.com>, Randy Dunlap <rdunlap@...radead.org>,
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Subject: Re: [外部邮件] Re: [PATCH][v3] hung_task: Panic after fixed number of hung tasks

On 2025/10/14 19:18, Li,Rongqing wrote:
>>>>> 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.
>>
>> Cool. Sounds good to me!
>>
>>>
>>>>> --- a/kernel/hung_task.c
>>>>> +++ b/kernel/hung_task.c
>>>>> @@ -229,9 +232,11 @@ 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) {
>>>>> +	if (sysctl_hung_task_panic &&
>>>>> +			(total_hung_task >= sysctl_hung_task_panic)) {
>>>>>     		console_verbose();
>>>>>     		hung_task_show_lock = true;
>>>>>     		hung_task_call_panic = true;
>>>
>>> I would expect that this patch added another counter, similar to
>>> sysctl_hung_task_detect_count. It would be incremented only once per
>>> check when a hung task was detected. And it would be cleared (reset)
>>> when no hung task was found.
>>
>> Much cleaner. We could add an internal counter for that, yeah. No need to
>> expose it to userspace ;)
>>
>> Petr's suggestion seems to align better with the goal of panicking on
>> persistent hangs, IMHO. Panic after N consecutive checks with hung tasks.
>>
>> @RongQing does that work for you?
> 
> 
> In my opinion, a single task hang is not a critical issue, fatal hangs—such as those caused by I/O hangs, network card failures, or hangs while holding locks—will inevitably lead to multiple tasks being hung. In such scenarios, users cannot even log in to the machine, making it extremely difficult to investigate the root cause. Therefore, I believe the current approach is sound. What's your opinion?

Thanks! I'm fine with either approach. Let's hear what the other folks 
think ;)