From mboxrd@z Thu Jan 1 00:00:00 1970 From: tytso@mit.edu Subject: Re: [PATCH] ext4_freeze: don't return to userspace with a mutex held Date: Sun, 4 Apr 2010 17:03:02 -0400 Message-ID: <20100404210302.GL18524@thunk.org> References: <4BB12B03.9070906@redhat.com> <20100404205237.GK18524@thunk.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: ext4 development To: Eric Sandeen Return-path: Received: from THUNK.ORG ([69.25.196.29]:39399 "EHLO thunker.thunk.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751115Ab0DDVDE (ORCPT ); Sun, 4 Apr 2010 17:03:04 -0400 Content-Disposition: inline In-Reply-To: <20100404205237.GK18524@thunk.org> Sender: linux-ext4-owner@vger.kernel.org List-ID: On Sun, Apr 04, 2010 at 04:52:37PM -0400, tytso@MIT.EDU wrote: > On Mon, Mar 29, 2010 at 05:34:43PM -0500, Eric Sandeen wrote: > > > > I don't -think- we need to do this; by now we should have s_frozen > > set, and nobody else should be coming down the pipe to get to > > the journal. However, just to be on the safe side, I added > > a couple of vfs_check_frozen() calls in ext4 functions which will > > arrive at start_this_handle(), which should ensure that we never > > get any journal traffic generated while frozen. > > Um, I think the addition of vfs_check_frozen(), esp. to > ext4_journal_start_sb() is absolutely necessary. What else do we have > to prevent filesystem modifications from going to the file systme > layer? I didn't see anything in the VFS layer that checks s_frozen; > am I missing something? Added to the ext4 patch queue, with the following patch comment: ext4: don't return to userspace after freezing the fs with a mutex held ext4_freeze() used jbd2_journal_lock_updates() which takes the j_barrier mutex, and then returns to userspace. The kernel does not like this: ================================================ [ BUG: lock held when returning to user space! ] ------------------------------------------------ lvcreate/1075 is leaving the kernel with locks still held! 1 lock held by lvcreate/1075: #0: (&journal->j_barrier){+.+...}, at: [] jbd2_journal_lock_updates+0xe1/0xf0 Use vfs_check_frozen() added to ext4_journal_start_sb() and ext4_force_commit() instead. Addresses-Red-Hat-Bugzilla: #568503 Signed-off-by: Eric Sandeen Signed-off-by: "Theodore Ts'o" - Ted