From mboxrd@z Thu Jan 1 00:00:00 1970 From: Dave Chinner Subject: Re: [PATCH 2/5] fsfreeze: emergency thaw will deadlock on s_umount Date: Tue, 15 Jun 2010 09:21:50 +1000 Message-ID: <20100614232150.GI6590@dastard> References: <1276154395-24766-1-git-send-email-david@fromorbit.com> <1276154395-24766-3-git-send-email-david@fromorbit.com> <20100614152011.GB32354@infradead.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, viro@ZenIV.linux.org.uk, josef@redhat.com, jeffmerkey@gmail.com To: Christoph Hellwig Return-path: Content-Disposition: inline In-Reply-To: <20100614152011.GB32354@infradead.org> Sender: linux-kernel-owner@vger.kernel.org List-Id: linux-fsdevel.vger.kernel.org On Mon, Jun 14, 2010 at 11:20:11AM -0400, Christoph Hellwig wrote: > On Thu, Jun 10, 2010 at 05:19:51PM +1000, Dave Chinner wrote: > > The emergency thaw process uses iterate_super() which holds the > > sb->s_umount lock in read mode. The current thaw_super() code takes > > the sb->s_umount lock in write mode, hence leading to an instant > > deadlock. > > > > Pass the emergency state into the thaw_bdev/thaw_super code to avoid > > taking the s_umount lock in this case. We are running under the bdev > > freeze mutex, so this is still serialised against freeze despite > > only having a read lock on the sb->s_umount. Hence it should be safe > > to execute in this manner, especially given that emergency thaw is a > > rarely executed "get-out-of-jail" feature. > > This is correct as long as no one calls thaw_super directly, which > is not the case currently. Yeah, the idea of the first two patches is that they can be applied to a current tree and backported and prevent the infinite loop or deadlock. The problem of thaw_bdev/thaw_super is what the rest of the patches are supposed to address. Cheers, Dave. -- Dave Chinner david@fromorbit.com