linux-kernel - Re: Sleeping in RCU list traversal

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Date:	Sun, 7 Oct 2007 22:26:23 +0900
From:	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To:	junwang1234@...il.com, a.p.zijlstra@...llo.nl
Cc:	linux-kernel@...r.kernel.org, linux-security-module@...r.kernel.org
Subject: Re: Sleeping in RCU list traversal

Hello.

Thank you for pointing out.

Jun WANG wrote:
> >rcu_read_lock();
> >list_for_each_rcu(p, ...) {
> >   ptr = list_entry(p, struct ..., list);
> >   /* Grab a reference to "ptr". */
> >   rcu_read_unlock();
> >   my_task_that_may_sleep(ptr);
> >   rcu_read_lock();
> >   /* Drop a reference to "ptr". */
> > }
> > rcu_read_unlock();
> 
> In Document/RCU/whatisRCU.txt
> Note that the value returned by rcu_dereference() is valid
> 	only within the enclosing RCU read-side critical section.
Excuse me, but I think "p" is used only between rcu_read_lock() and rcu_read_unlock().
Is it illegal to use "ptr" after rcu_read_unlock() if "ptr" is obtained before rcu_read_unlock() ?

Regards.

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