Re: [PATCH -next 1/8] rcu: Fix rcu_read_unlock() deadloop due to softirq

[Yao Kai <yaokai34@huawei.com>]

On 1/3/2026 8:41 AM, Joel Fernandes wrote:
> 
> 
> On 1/2/2026 2:51 PM, Paul E. McKenney wrote:
>> On Fri, Jan 02, 2026 at 12:30:09PM -0500, Steven Rostedt wrote:
>>> On Fri, 2 Jan 2026 12:28:07 -0500
>>> Steven Rostedt <rostedt@goodmis.org> wrote:
>>>
>>>> Stacktrace should have recursion protection too.
>>>>
>>>> Can you try this patch to see if it would have fixed the problem too?
>>>
>>> As I believe the recursion protection should be in the tracing
>>> infrastructure more than in RCU. As RCU is used as an active participant in
>>> the kernel whereas tracing is supposed to be only an observer.
>>>
>>> If tracing is the culprit, it should be the one that is fixed.
>>
>> Makes sense to me!  But then it would...  ;-)
>>
> Could we fix it in both? (RCU and tracing). The patch just adds 3 more net lines
> to RCU code. It'd be good to have a guard rail against softirq recursion in RCU
> read unlock path, as much as the existing guard rail we already have with
> irq_work? After all, both paths attempt to do deferred work when it is safer to
> do so.
> 
> Yao, if you could test Steve's patch and reply whether it fixes it too?
> 
> thanks,
> 
>   - Joel
> 
> 
> 
> 

Yes, I tested Steve's patch. It fixes the issue too.

Tested-by: Yao Kai <yaokai34@huawei.com>

  - Yao