From: Ted Ts'o Subject: Re: ext4: Fix data corruption with multi-block writepages support Date: Thu, 3 Feb 2011 13:38:55 -0500 Message-ID: <20110203183854.GA2623@thunk.org> References: Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: ext4 development , Jon Nelson To: Curt Wohlgemuth Return-path: Received: from li9-11.members.linode.com ([67.18.176.11]:33593 "EHLO test.thunk.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932312Ab1BCSjA (ORCPT ); Thu, 3 Feb 2011 13:39:00 -0500 Content-Disposition: inline In-Reply-To: Sender: linux-ext4-owner@vger.kernel.org List-ID: Thanks, added to the ext4 patch queue. I modified the commit description slightly to give credit to Jon Nelson, who reported the bug and really helped by devising a reproduceable test case. Many thanks, Jon!! - Ted ext4: Fix data corruption with multi-block writepages support From: Curt Wohlgemuth This fixes a corruption problem with the multi-block writepages submittal change for ext4, from commit bd2d0210cf22f2bd0cef72eb97cf94fc7d31d8cc ("ext4: use bio layer instead of buffer layer in mpage_da_submit_io"). (Note that this corruption is not present in 2.6.37 on ext4, because the corruption was detected after the feature was merged in 2.6.37-rc1, and so it was turned off by adding a non-default mount option, mblk_io_submit. With this commit, which hopefully fixes the last of the bugs with this feature, we'll be able to turn on this performance feature by default in 2.6.38, and remove the mblk_io_submit option.) The ext4 code path to bundle multiple pages for writeback in ext4_bio_write_page() had a bug: we should be clearing buffer head dirty flags *before* we submit the bio, not in the completion routine. The patch below was tested on 2.6.37 under KVM with the postgresql script which was submitted by Jon Nelson as documented in commit 1449032be1. Without the patch, I'd hit the corruption problem about 50-70% of the time. With the patch, I executed the script > 100 times with no corruption seen. I also fixed a bug to make sure ext4_end_bio() doesn't dereference the bio after the bio_put() call. Reported-by: Jon Nelson Signed-off-by: Curt Wohlgemuth Signed-off-by: "Theodore Ts'o"