linux-kernel - Re: [PATCH -next 1/8] rcu: Fix rcu_read

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Message-ID: <34ff0ff6-217e-4574-a3b1-af74b2f40937@huawei.com>
Date: Sun, 4 Jan 2026 11:20:07 +0800
From: Yao Kai <yaokai34@...wei.com>
To: Joel Fernandes <joelagnelf@...dia.com>, <paulmck@...nel.org>, Steven
 Rostedt <rostedt@...dmis.org>
CC: Boqun Feng <boqun.feng@...il.com>, <rcu@...r.kernel.org>, Frederic
 Weisbecker <frederic@...nel.org>, Neeraj Upadhyay
	<neeraj.upadhyay@...nel.org>, Josh Triplett <josh@...htriplett.org>,
	Uladzislau Rezki <urezki@...il.com>, Mathieu Desnoyers
	<mathieu.desnoyers@...icios.com>, Lai Jiangshan <jiangshanlai@...il.com>,
	Zqiang <qiang.zhang@...ux.dev>, Shuah Khan <shuah@...nel.org>,
	<linux-kernel@...r.kernel.org>, <linux-kselftest@...r.kernel.org>, Tengda Wu
	<wutengda2@...wei.com>, <liuyongqiang13@...wei.com>, <yujiacheng3@...wei.com>
Subject: Re: [PATCH -next 1/8] rcu: Fix rcu_read_unlock() deadloop due to
 softirq



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@...dmis.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@...wei.com>

  - Yao