From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754818AbaESO2L (ORCPT ); Mon, 19 May 2014 10:28:11 -0400 Received: from mail-qc0-f178.google.com ([209.85.216.178]:50785 "EHLO mail-qc0-f178.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754731AbaESO2H (ORCPT ); Mon, 19 May 2014 10:28:07 -0400 Date: Mon, 19 May 2014 10:28:02 -0400 From: Jeff Layton To: "Michael Kerrisk (man-pages)" Cc: "linux-man@vger.kernel.org" , lkml , Linux-Fsdevel , Andy Lutomirski Subject: Re: OFD locks and deadlock detection Message-ID: <20140519102802.16dee141@tlielax.poochiereds.net> In-Reply-To: <537A0495.60107@gmail.com> References: <537A0495.60107@gmail.com> X-Mailer: Claws Mail 3.9.3 (GTK+ 2.24.22; x86_64-redhat-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 19 May 2014 15:18:13 +0200 "Michael Kerrisk (man-pages)" wrote: > Hi Jeff, > > I just happened to notice : > > commit 57b65325fe34ec4c917bc4e555144b4a94d9e1f7 > Author: Jeff Layton > Date: Mon Feb 3 12:13:09 2014 -0500 > > locks: skip deadlock detection on FL_FILE_PVT locks > > And then this thread: > > http://thread.gmane.org/gmane.linux.file-systems/81318/focus=81327 > From: Jeff Layton redhat.com> > Subject: [PATCH v5 13/14] locks: skip deadlock detection on FL_FILE_PVT locks > Date: 2014-01-09 14:19:46 GMT > > I think it's pretty important to document that. All implementations > of traditional process-associated (.k.a. "POSIX") locks that I've ever > come across do detect deadlocks, so it's important to note that OFD locks > do not. > > I plan to add the following text to the fcntl(2) page: > > [[ > In the current implementation, > no deadlock detection is performed for open file description locks. > (This contrasts with process-associated record locks, > for which the kernel does perform deadlock detection.) > ]] > > Okay? > > cheers, > > Michael > > (note: I'm no longer with Red Hat, so jlayton@redhat.com no longer works) Sounds fine to me. FWIW, the deadlock detection for process-associated record locks is pretty worthless except in certain narrow circumstances. At some point, we probably should have a discussion as to whether deadlock detection is really something we want to keep. The current implementation requires a global spinlock which has obvious consequences for scalability. Thanks, -- Jeff Layton