Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756055Ab1BXSzm (ORCPT ); Thu, 24 Feb 2011 13:55:42 -0500 Received: from e38.co.us.ibm.com ([32.97.110.159]:44626 "EHLO e38.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754186Ab1BXSzh (ORCPT ); Thu, 24 Feb 2011 13:55:37 -0500 Date: Thu, 24 Feb 2011 10:27:32 -0800 From: "Darrick J. Wong" To: Chris Mason Cc: Jan Kara , Joel Becker , "Martin K. Petersen" , Jens Axboe , linux-kernel , linux-fsdevel , Mingming Cao , linux-scsi Subject: Re: [RFC] block integrity: Fix write after checksum calculation problem Message-ID: <20110224182732.GV27190@tux1.beaverton.ibm.com> Reply-To: djwong@us.ibm.com References: <20110222020022.GH32261@tux1.beaverton.ibm.com> <20110223202446.GG4020@noexit> <1298493173-sup-8301@think> <20110224164758.GH23042@quack.suse.cz> <1298566775-sup-730@think> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1298566775-sup-730@think> User-Agent: Mutt/1.5.17+20080114 (2008-01-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2616 Lines: 51 On Thu, Feb 24, 2011 at 12:37:53PM -0500, Chris Mason wrote: > Excerpts from Jan Kara's message of 2011-02-24 11:47:58 -0500: > > On Wed 23-02-11 15:35:11, Chris Mason wrote: > > > Excerpts from Joel Becker's message of 2011-02-23 15:24:47 -0500: > > > > On Tue, Feb 22, 2011 at 11:45:44AM -0500, Martin K. Petersen wrote: > > > > > Also, DIX is only the tip of the iceberg. Many other impending > > > > > technologies feature checksums and require pages to be stable during I/O > > > > > due to checksumming, encryption and so on. > > > > > > > > > > The VM is already trying to do the right thing. We just need the > > > > > relevant filesystems to catch up. > > > > > > > > ocfs2 handles stable metadata for its checksums when feeding > > > > things to the journal. If we're doing pagecache-based I/O, is the > > > > pagecache going to help here for data? > > > > > > Data is much easier than metadata. All you really need is to wait on > > > writeback in file_write, wait on writeback in page_mkwrite, and make > > > sure you don't free blocks back to the allocator that are actively under > > > IO. > > > > > > I expect the hard part to be jbd and metadata in ext34. > > But JBD already has to do data copy if a buffer is going to be modified > > before/while it is written to the journal. So we should alredy do all that > > is needed for metadata. I don't say there aren't any bugs as they could be > > triggered only by crashing at the wrong moment and observing fs corruption. > > But most of the work should be there... > > Most of it is there, but there are always little bits and pieces. The > ext4 journal csumming code was one semi-recent example where we found > metadata changing in flight. > > A big part of testing this is getting some way to detect the bugs > without dif/dix. With btrfs I have patches to do set_memory_ro on > pages once I've don the crc, hopefully we can generalize that idea or > some up with something smarter. Right now I'm faking it with modprobe scsi_debug ato=1 guard=1 dif=3 dix=199. Hm, would you mind sharing those patches? I've been working on a second patch to do the wait-on-writeback per everyone's suggestions, but I still see the occasional corruption error as soon as I enable the mmap write case and covet some more debugging tools. It does seem to be working for the pure pwrite() case. :) --D -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/