Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756363AbXITGV0 (ORCPT ); Thu, 20 Sep 2007 02:21:26 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752508AbXITGVT (ORCPT ); Thu, 20 Sep 2007 02:21:19 -0400 Received: from ecfrec.frec.bull.fr ([129.183.4.8]:47737 "EHLO ecfrec.frec.bull.fr" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752092AbXITGVS (ORCPT ); Thu, 20 Sep 2007 02:21:18 -0400 Message-ID: <46F2123A.9070201@bull.net> Date: Thu, 20 Sep 2007 08:24:58 +0200 From: Nadia Derbey Organization: BULL/DT/OSwR&D/Linux User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.6) Gecko/20040115 X-Accept-Language: en-us, en MIME-Version: 1.0 To: Jarek Poplawski Cc: Andrew Morton , Alexey Dobriyan , linux-kernel@vger.kernel.org Subject: Re: 2.6.23-rc6-mm1: IPC: sleeping function called ... References: <20070919140726.GA4603@ff.dom.local> In-Reply-To: <20070919140726.GA4603@ff.dom.local> X-MIMETrack: Itemize by SMTP Server on ECN002/FR/BULL(Release 5.0.12 |February 13, 2003) at 20/09/2007 08:25:12, Serialize by Router on ECN002/FR/BULL(Release 5.0.12 |February 13, 2003) at 20/09/2007 08:25:14, Serialize complete at 20/09/2007 08:25:14 Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset=us-ascii; format=flowed Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1622 Lines: 46 Jarek Poplawski wrote: > 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? 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(). Regards, Nadia - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/