From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751215AbWHPRM3 (ORCPT ); Wed, 16 Aug 2006 13:12:29 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751190AbWHPRMJ (ORCPT ); Wed, 16 Aug 2006 13:12:09 -0400 Received: from pentafluge.infradead.org ([213.146.154.40]:46506 "EHLO pentafluge.infradead.org") by vger.kernel.org with ESMTP id S1750775AbWHPRL6 (ORCPT ); Wed, 16 Aug 2006 13:11:58 -0400 Subject: Re: [PATCH] IB/uverbs: Fix lockdep warning when QP is created with 2 CQs From: Arjan van de Ven To: Roland Dreier Cc: openib-general@openib.org, linux-kernel@vger.kernel.org In-Reply-To: References: Content-Type: text/plain Organization: Intel International BV Date: Wed, 16 Aug 2006 19:11:23 +0200 Message-Id: <1155748283.3023.76.camel@laptopd505.fenrus.org> Mime-Version: 1.0 X-Mailer: Evolution 2.2.3 (2.2.3-2.fc4) Content-Transfer-Encoding: 7bit X-SRS-Rewrite: SMTP reverse-path rewritten from by pentafluge.infradead.org See http://www.infradead.org/rpr.html Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 2006-08-16 at 09:43 -0700, Roland Dreier wrote: > Arjan, here's a case that disproves your rule of thumb that rwsems > are equivalent to mutexes as far as correctness goes: you can't have > an AB-BA deadlock with nested rwsems when using down_read(). In other > words, the following: > > down_read(&lock_1); > down_read(&lock_2); > down_read(&lock_2); > down_read(&lock_1); > > is perfectly safe it's safe as long as you never ever do a down_write nested inside or outside a down_read of any of these locks.... -- if you want to mail me at work (you don't), use arjan (at) linux.intel.com