Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755766AbZCLKIR (ORCPT ); Thu, 12 Mar 2009 06:08:17 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1755633AbZCLKHx (ORCPT ); Thu, 12 Mar 2009 06:07:53 -0400 Received: from bombadil.infradead.org ([18.85.46.34]:51191 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755606AbZCLKHw (ORCPT ); Thu, 12 Mar 2009 06:07:52 -0400 Subject: Re: [PATCH 3/6] futex: add double_unlock_hb() From: Peter Zijlstra To: Darren Hart Cc: linux-kernel@vger.kernel.org, Thomas Gleixner , Ingo Molnar , Rusty Russell In-Reply-To: <20090312075552.9856.48021.stgit@Aeon> References: <20090312075349.9856.83687.stgit@Aeon> <20090312075552.9856.48021.stgit@Aeon> Content-Type: text/plain Date: Thu, 12 Mar 2009 11:07:35 +0100 Message-Id: <1236852455.5090.105.camel@laptop> Mime-Version: 1.0 X-Mailer: Evolution 2.25.92 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 923 Lines: 20 On Thu, 2009-03-12 at 00:55 -0700, Darren Hart wrote: > The futex code uses double_lock_hb() which locks the hb->lock's in pointer > value order. There is no parallel unlock routine, and the code unlocks them > in name order, ignoring pointer value. This opens up a window for an ABBA > deadlock. This patch adds double_unlock_hb() to remove the window as well > as refactor the duplicated code segments. While I don't mind the patch per-se, I'm hard pressed to see any deadlock potential in the unordered unlock. All sites (at least those in the patch) always release both locks without taking another in between, therefore one would think there's no deadlock possible. -- 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/