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

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Message-ID: <20070920082105.GB2065@ff.dom.local>
Date:	Thu, 20 Sep 2007 10:21:05 +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 Thu, Sep 20, 2007 at 09:28:21AM +0200, Jarek Poplawski wrote:
> On Thu, Sep 20, 2007 at 08:24:58AM +0200, Nadia Derbey wrote:
...
> > Before Calling msg_unlock() they call ipc_rcu_getref() that increments a 
> > refcount in the rcu header for the msg structure. This guarantees that 
> > the the structure won't be freed before they relock it. Once the 
> > structure is relocked by ipc_lock_by_ptr(), they do the symmetric 
> > operation i.e. ipc_rcu_putref().
...
> which seems to suggest "out" is an RCU protected pointer, so, I
> thought these refcounts were for something else. But, after looking
> at how it's used it turns out to be ~90% wrong: probably 9 out of 10
> places use refcouning around this, so, these rcu_read_locks() don't
> work here at all. So, probably I miss something again, but IMHO,
> these rcu_read_locks/unlocks could be removed here or in
...
...So I missed it again: after all this RCU protection works before
and after refcounting.

Sorry,
Jarek P.
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