Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755249AbXJ1Xbc (ORCPT ); Sun, 28 Oct 2007 19:31:32 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752408AbXJ1XbW (ORCPT ); Sun, 28 Oct 2007 19:31:22 -0400 Received: from palinux.external.hp.com ([192.25.206.14]:33473 "EHLO mail.parisc-linux.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752206AbXJ1XbV (ORCPT ); Sun, 28 Oct 2007 19:31:21 -0400 Date: Sun, 28 Oct 2007 17:31:20 -0600 From: Matthew Wilcox To: Jiri Kosina Cc: Trond Myklebust , Alan Cox , "J. Bruce Fields" , Linus Torvalds , linux-kernel@vger.kernel.org, "George G. Davis" , Andrew Morton , linux-fsdevel@vger.kernel.org Subject: Re: [RFC, PATCH] locks: remove posix deadlock detection Message-ID: <20071028233119.GE32359@parisc-linux.org> References: <20071026170750.GC13033@fieldses.org> <20071026224707.GO13033@fieldses.org> <20071028173136.GA16905@fieldses.org> <20071028174321.GB16905@fieldses.org> <20071028182732.GK27248@parisc-linux.org> <20071028184052.49abd092@the-village.bc.nu> <20071028201101.GA32359@parisc-linux.org> <1193608230.7561.11.camel@heimdal.trondhjem.org> <20071028224157.GC32359@parisc-linux.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.13 (2006-08-11) Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1590 Lines: 37 On Sun, Oct 28, 2007 at 11:55:52PM +0100, Jiri Kosina wrote: > On Sun, 28 Oct 2007, Matthew Wilcox wrote: > > > Bzzt. You get a false deadlock with multiple threads like so: > > Thread A of task B takes lock 1 > > Thread C of task D takes lock 2 > > Thread C of task D blocks on lock 1 > > Thread E of task B blocks on lock 2 > > A potential for deadlock occurs if a process controlling a locked > region is put to sleep by attempting to lock another process' > locked region. If the system detects that sleeping until a locked > region is unlocked would cause a deadlock, fcntl() shall fail with > an [EDEADLK] error. > > This is what POSIX says [1], even after being modified with respect to > POSIX Threads Extension, right? > > So it doesn't deal with threads at all, just processess are taken into > account. Probably for a reason :) Did you have a concrete suggestion, or are you just quoting the spec? The problem is that it's nonsense -- processes don't sleep, threads do. I think the key is "would deadlock", not "might deadlock". Our current behaviour is clearly in violation of SuSv3. -- Intel are signing my paycheques ... these opinions are still mine "Bill, look, we understand that you're interested in selling us this operating system, but compare it to ours. We can't possibly take such a retrograde step." - 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/