linux-kernel - Re: 2.6.23-rc6-mm1: IPC: sleeping function called ...

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Date:	Wed, 19 Sep 2007 16:07:26 +0200
From:	Jarek Poplawski <jarkao2@...pl>
To:	Nadia Derbey <Nadia.Derbey@...l.net>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Alexey Dobriyan <adobriyan@...ru>, linux-kernel@...r.kernel.org
Subject: Re: 2.6.23-rc6-mm1: IPC: sleeping function called ...

On 18-09-2007 16:55, Nadia Derbey wrote:
...
> 
> Well, reviewing the code I found another place where the 
> rcu_read_unlock() was missing.
> I'm so sorry for the inconvenience. It's true that I should have tested 
> with CONFIG_PREEMPT=y :-(
> Now, the ltp tests pass even with this option set...
> 
> In attachment you'll find a patch thhat
> 1) adds the missing rcu_read_unlock()
> 2) replaces Andrew's fix with a new one: the rcu_read_lock() is now 
> taken in ipc_lock() / ipc_lock_by_ptr() and released in ipc_unlock(), 
> exactly as it was done in the ref code.

BTW, probably I miss something, but I wonder, how this RCU is working
here. E.g. in msg.c do_msgsnd() there is:

msq = msg_lock_check(ns, msqid);
...

msg_unlock(msq);
schedule();

ipc_lock_by_ptr(&msq->q_perm);

Since msq_lock_check() gets msq with ipc_lock_check() under
rcu_read_lock(), and then goes msg_unlock(msq) (i.e. ipc_unlock())
with rcu_read_unlock(), is it valid to use this with
ipc_lock_by_ptr() yet?

Regards,
Jarek P.
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