From: Jeff Layton Subject: Re: [2.6.26-rc4] mount.nfsv4/memory poisoning issues... Date: Tue, 10 Jun 2008 16:13:52 -0400 Message-ID: <20080610161352.4e588653@tleilax.poochiereds.net> References: <6278d2220806041633n3bfe3dd2ke9602697697228b@mail.gmail.com> <20080604203504.62730951@tleilax.poochiereds.net> <1213124088.20459.16.camel@localhost> <20080610151357.150b6f69@tleilax.poochiereds.net> <1213127909.20459.48.camel@localhost> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Cc: Daniel J Blueman , linux-nfs@vger.kernel.org, nfsv4@linux-nfs.org, Linux Kernel To: Trond Myklebust Return-path: Received: from mx1.redhat.com ([66.187.233.31]:36169 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751257AbYFJUOK (ORCPT ); Tue, 10 Jun 2008 16:14:10 -0400 In-Reply-To: <1213127909.20459.48.camel@localhost> Sender: linux-nfs-owner@vger.kernel.org List-ID: On Tue, 10 Jun 2008 15:58:29 -0400 Trond Myklebust wrote: > On Tue, 2008-06-10 at 15:13 -0400, Jeff Layton wrote: > > > I think you're basically correct, but it looks to me like the > > nfs_callback_mutex actually protects nfs_callback_info.task as well. > > > > If we're starting the thread, then we can't call kthread_stop on it > > until we release the mutex. So the thread can't exit until we release > > the mutex, and we can be guaranteed that this: > > > > nfs_callback_info.task = NULL; > > > > ...can't happen until after kthread_run returns and nfs_callback_up > > sets it. > > > > If that's right, then maybe this (untested, RFC only) patch would make sense? > > Hmm... I suppose that is correct, but what if nfs_alloc_client() does > > nfs_callback_up(); > > nfs_callback_down(); > > AFAICS, if nfs_callback_down() gets called before the kthread() function > gets scheduled back in, then you can get left with a value of > nfs_callback_info.task != NULL, since nfs_callback_svc() will never be > called. > I don't see this race. We can't call nfs_callback_down() until after nfs_callback_up() returns, so we're guaranteed to have "task" set to a valid task (presuming that nfs_callback_up() doesn't return error). We also can't return from nfs_callback_down() until after the nfs_callback_svc() has exited. kthread_stop() will block until it does. > Wouldn't it therefore make more sense to clear nfs_callback_info.task in > nfs_callback_down()? > I suppose that makes just as much sense. It also seems more symmetrical given that we also set the var in nfs_callback_up(). I'll roll that into the BKL removal patch, and give it some testing. Look for it in a day or two... Thanks, -- Jeff Layton