linux-kernel - Re: Question on (locking: Make spinlock_t and rwlock

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Message-ID: <20210730144427.357annugmfjap24e@linutronix.de>
Date:   Fri, 30 Jul 2021 16:44:27 +0200
From:   Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:     "Zhang, Qiang" <Qiang.Zhang@...driver.com>
Cc:     "linux-rt-users@...r.kernel.org" <linux-rt-users@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: Question on (locking: Make spinlock_t and rwlock_t a RCU section
 on RT)

On 2021-07-26 07:43:33 [+0000], Zhang, Qiang wrote:
> Operation of sleep is not allowed in RCU read critical area,  If
> after acquiring a rt-spinlock , try to acquire another one
> rt-spinlock,  This may cause sleep, and trigger RCU warning.  
> 
> Is there a problem with my analysis or something I missed?

This warning is suppressed on RT. Same as on CONFIG_PREEMPT when a task
gets preempted while in a rcu_read_lock() section.

> Thanks
> Qiang

Sebastian