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

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Message-ID: <4dbe929b-7864-4cee-8f19-d0db970ef95a@efficios.com>
Date: Thu, 8 Jan 2026 10:57:41 -0500
From: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To: Frederic Weisbecker <frederic@...nel.org>,
 Joel Fernandes <joel@...lfernandes.org>
Cc: Joel Fernandes <joelagnelf@...dia.com>,
 Paul E McKenney <paulmck@...nel.org>, Boqun Feng <boqun.feng@...il.com>,
 rcu@...r.kernel.org, Neeraj Upadhyay <neeraj.upadhyay@...nel.org>,
 Josh Triplett <josh@...htriplett.org>, Uladzislau Rezki <urezki@...il.com>,
 Steven Rostedt <rostedt@...dmis.org>, 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, Kai Yao <yaokai34@...wei.com>,
 Tengda Wu <wutengda2@...wei.com>
Subject: Re: [PATCH -next 1/8] rcu: Fix rcu_read_unlock() deadloop due to
 softirq

On 2026-01-08 10:39, Frederic Weisbecker wrote:
> Le Wed, Jan 07, 2026 at 10:35:44PM -0500, Joel Fernandes a écrit :
>>>
>>> By the way, when I last tried to do it from rcu_qs, it was not fixing the original bug with the IRQ work recursion.
>>>
>>> I found that it was always resetting the flag. But probably it is not even the right place to do it in the first place.
>>
>> I think we need to reset the flag in rcu_report_exp_rdp() as well if exp_hint
>> is set and we reported exp qs.
> 
> To avoid needlessly reaching the rcu_read_unlock() slowpath whenever the exp QS has
> already been reported, yes indeed.

This seems related to:

https://lore.kernel.org/lkml/6c96dbb5-bffc-423f-bb6a-3072abb5f711@efficios.com/

Is it the same issue ?

Thanks,

Mathieu

-- 
Mathieu Desnoyers
EfficiOS Inc.
https://www.efficios.com