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

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Message-ID: <166bc5aa-a715-438e-8805-c74c2b5fc83b@nvidia.com>
Date: Wed, 2 Jul 2025 06:59:38 -0400
From: Joel Fernandes <joelagnelf@...dia.com>
To: Qi Xi <xiqi2@...wei.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



On 7/2/2025 5:14 AM, Qi Xi wrote:
> 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);
> +}

Oh gosh, thanks for spotting that! Indeed,  I had changed it to != 0 in the last
version but applied an older patch. I will fix it in the tree. Thank you again!

Neeraj, would you like this as a separate commit that you can then squash? Or
could you fix it up in your tree?

 - Joel