Re: [v6 PATCH 0/2] hung_task: Provide runtime reset interface for hung task detector

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

On 2026/1/20 17:46, Petr Mladek wrote:
> On Fri 2026-01-16 10:22:34, Lance Yang wrote:
>>
>>
>> On 2026/1/16 02:18, Aaron Tomlin wrote:
>>> On Thu, Jan 15, 2026 at 11:24:13AM +0800, Lance Yang wrote:
>>>> IIUC, we should just do:
>>>> - Patch 1: Full cmpxchg-based counting (Petr's POC), sysctl read-only
>>>> - Patch 2: Add write handler for userspace reset
>>>>
>>>> That way Patch 1 is the real logic change, and Patch 2 is just adding
>>>> the userspace interface.
>>>
>>> Hi Lance,
>>>
>>> Thank you for your feedback.
>>> If I am not mistaken, Joel suggested the following structure [1]:
>>>
>>>       1. Create a preparatory patch to change the data type to atomic_long_t
>>>       2. Introduce the required functionality to support a reset to "0"
>>>
>>> [1]: https://lore.kernel.org/lkml/d4vx6k7d4tlagesq55yrbma26i2nyt4tpijkme6ckioeyfqfec@txrs27niaj2m/
>>>
>>
>> Yeah, either way works :)
>>
>> But that way (changing to atomic with the old logic first, then
>> rewriting to the new logic) seems like it creates more churn
>> and makes review harder.
> 
> I agree that adding the atomic and keeping the old logic is not
> good. I would prefer to split it into two patches the following
> way:
> 
>    1. Reshufle the code so that "sysctl_hung_task_detect_count"
>       gets incremented in check_hung_uninterruptible_tasks()
>       and hung_task_info() will just get "this_round_count".
> 
>       Plus convert "sysctl_hung_task_detect_count" to atomic.
> 
>       It is the change that I suggested at
>       https://lore.kernel.org/lkml/aWTzhLSWQRIGt8Xu@pathway.suse.cz/
> 
>       This way, it would be clear why the reshufling was done.
>       And the atomic operations will get the right acquire/release
>       semantic right away.
> 
> 
>     2. Add support to reset the couter to "0".
> 
>        It should be a quite simple patch easy to review.

+1

Thanks,
Lance

> 
> 
> I think that this is how Joel meant it. We could even have 3 patches:
> 
>     1. Move "sysctl_hung_task_detect_count" increment to
>        check_hung_uninterruptible_tasks().
> 
>     2. Convert the counter to atomic operations.
> 
>     3. Add reset to "0" support.
> 
> But I think that two patches might be good enough.
> 
> Best Regards,
> Petr