From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S265966AbUGIUEf (ORCPT ); Fri, 9 Jul 2004 16:04:35 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S265959AbUGIUDZ (ORCPT ); Fri, 9 Jul 2004 16:03:25 -0400 Received: from fw.osdl.org ([65.172.181.6]:12710 "EHLO mail.osdl.org") by vger.kernel.org with ESMTP id S265955AbUGIUB5 (ORCPT ); Fri, 9 Jul 2004 16:01:57 -0400 Date: Fri, 9 Jul 2004 13:00:45 -0700 From: Andrew Morton To: Jesse Stockall Cc: s.rivoir@gts.it, linux-kernel@vger.kernel.org, stern@rowland.harvard.edu Subject: Re: 2.6.7-mm7 Message-Id: <20040709130045.211b6d50.akpm@osdl.org> In-Reply-To: <1089402736.8067.12.camel@homer.blizzard.org> References: <20040708235025.5f8436b7.akpm@osdl.org> <40EE5418.2040000@gts.it> <20040709024112.7ef44d1d.akpm@osdl.org> <40EE732C.5020404@gts.it> <1089373506.8067.7.camel@homer.blizzard.org> <20040709115411.23d96699.akpm@osdl.org> <1089402736.8067.12.camel@homer.blizzard.org> X-Mailer: Sylpheed version 0.9.7 (GTK+ 1.2.10; i386-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 X-Mailing-List: linux-kernel@vger.kernel.org Jesse Stockall wrote: > > On Fri, 2004-07-09 at 14:54, Andrew Morton wrote: > down_write_trylock(&usb_all_devices_rwsem)); > > > > That's a bit unusual. Could you (or Alan) please explain the reason for > > this a little more? > > I believe you want this thread > > http://marc.theaimsgroup.com/?l=linux-usb-devel&m=108923404032264&w=2 Oh, OK. Recursively taking an rwsem for reading is certainly deadlocky. The main reason for not supporting this is that heavy down_read() traffic can trivially livelock down_write() waiters. Alan's patch will introduce that shortcoming. Really, it would be better to get the locking sorted out.