From: Theodore Tso Subject: Re: [PATCH 3/5] ext4: ext4_mark_recovery_complete() doesn't need to use lock_super Date: Sun, 26 Apr 2009 07:46:08 -0400 Message-ID: <20090426114608.GC10248@mit.edu> References: <1240717765-16572-1-git-send-email-tytso@mit.edu> <1240717765-16572-2-git-send-email-tytso@mit.edu> <1240717765-16572-3-git-send-email-tytso@mit.edu> <1240717765-16572-4-git-send-email-tytso@mit.edu> <20090426070713.GA17022@infradead.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Ext4 Developers List , Linux Kernel Developers List , Al Viro To: Christoph Hellwig Return-path: Content-Disposition: inline In-Reply-To: <20090426070713.GA17022@infradead.org> Sender: linux-kernel-owner@vger.kernel.org List-Id: linux-ext4.vger.kernel.org On Sun, Apr 26, 2009 at 03:07:14AM -0400, Christoph Hellwig wrote: > On Sat, Apr 25, 2009 at 11:49:23PM -0400, Theodore Ts'o wrote: > > The function ext4_mark_recovery_complete() is called from two call > > paths: either (a) while mounting the filesystem, in which case there's > > no danger of any other CPU calling write_super() until the mount is > > completed, and (b) while remounting the filesystem read-write, in > > which case the fs core has already locked the superblock, and in any > > case write_super() wouldn't be called until the filesystem is > > successfully changed from being mounted read-only to read-write. > > Currently ext4_remount releases/reqacquires lock_super around > ext4_mark_recovery_complete, and unfortunately currently ->write_super > can be called on a r/o filesystem (that's why we have the MS_RDONLY > checks in all instance, I plan to clean that mess up). That's true, but the patch also takes out the release/reacquire in in ext4_remount (which was particularly ugly, belch). So even if write_super gets called on an r/o filesystem (why?!?), we should be safe because remount will hold lock_super() throughout the entire remount operation. We could delay this cleanup until you clean the mess with write_super, but I don't think it would be harmful in removing the lock_super()/unlock_super() pair in ext4_mark_recovery_complete(), and the unlock_super()/lock_super() pair in ext4_remount before then. Am I missing something? - Ted