From: Christoph Hellwig Subject: Re: [PATCH 3/5] ext4: ext4_mark_recovery_complete() doesn't need to use lock_super Date: Sun, 26 Apr 2009 03:07:14 -0400 Message-ID: <20090426070713.GA17022@infradead.org> 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> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Ext4 Developers List , Linux Kernel Developers List , Christoph Hellwig , Al Viro To: Theodore Ts'o Return-path: Content-Disposition: inline In-Reply-To: <1240717765-16572-4-git-send-email-tytso@mit.edu> Sender: linux-kernel-owner@vger.kernel.org List-Id: linux-ext4.vger.kernel.org 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). So for now I would keep that instance of lock_super, it'll also serve as documentation for the locking requirements once we pushed down lock_super to the filesystem in ->write_super and ->remount_fs so that it can eventually be replaced with an ext4-local lock.