linux-kernel - Re: [QUESTION] problems report: rcu_read_unlock_special() called in irq

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Message-ID: <506d8c4e-c317-4c85-9bcf-695596551d28@huawei.com>
Date: Wed, 2 Jul 2025 17:14:38 +0800
From: Qi Xi <xiqi2@...wei.com>
To: Joel Fernandes <joelagnelf@...dia.com>, <paulmck@...nel.org>, "Xiongfeng
 Wang" <wangxiongfeng2@...wei.com>
CC: Joel Fernandes <joel@...lfernandes.org>, <ankur.a.arora@...cle.com>,
	Frederic Weisbecker <frederic@...nel.org>, Boqun Feng <boqun.feng@...il.com>,
	<neeraj.upadhyay@...nel.org>, <urezki@...il.com>, <rcu@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, "Wangshaobo (bobo)"
	<bobo.shaobowang@...wei.com>, Xie XiuQi <xiexiuqi@...wei.com>
Subject: Re: [QUESTION] problems report: rcu_read_unlock_special() called in
 irq_exit() causes dead loop

Hi Joel,

After applying the 2 patches, the problem still exists. Compared to the 
previous fixes which did solve the problem, the difference is 
ct_in_irq() in the first patch.

I am wondering why "nesting != CT_NESTING_IRQ_NONIDLE" is added?


(previous fix: problem is solved)

+bool ct_in_irq(void)
+{
+    return ct_nmi_nesting() != 0;
+}

(current fix: problem still exists)

+bool ct_in_irq(void)
+{
+    long nesting = ct_nmi_nesting();
+
+    return (nesting && nesting != CT_NESTING_IRQ_NONIDLE);
+}


On 2025/7/1 21:29, Joel Fernandes wrote:
>
> On 7/1/2025 5:20 AM, Qi Xi wrote:
>> Hello everyone,
>>
>> Friendly ping about this problem :)
>>
> Ah, thanks for checking. The fix is slated for kernel 6.17.
>
> If you want to test it, could you apply it in advance from the RCU tree?
>
> You need these 2:
>
> https://git.kernel.org/pub/scm/linux/kernel/git/rcu/linux.git/commit/?h=next&id=6758c93749f8bf09b9282f100c5dd0a5c501f91c
>
> https://git.kernel.org/pub/scm/linux/kernel/git/rcu/linux.git/commit/?h=next&id=3cd298bf3bb69e3bca6abfe97e1b44ffa37f3dee
>
> Thanks.