Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754216Ab1BXRjG (ORCPT ); Thu, 24 Feb 2011 12:39:06 -0500 Received: from rcsinet10.oracle.com ([148.87.113.121]:33530 "EHLO rcsinet10.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753692Ab1BXRjC (ORCPT ); Thu, 24 Feb 2011 12:39:02 -0500 Content-Type: text/plain; charset=UTF-8 From: Chris Mason To: Jan Kara Cc: Joel Becker , "Martin K. Petersen" , djwong , Jens Axboe , linux-kernel , linux-fsdevel , Mingming Cao , linux-scsi Subject: Re: [RFC] block integrity: Fix write after checksum calculation problem In-reply-to: <20110224164758.GH23042@quack.suse.cz> References: <20110222020022.GH32261@tux1.beaverton.ibm.com> <20110223202446.GG4020@noexit> <1298493173-sup-8301@think> <20110224164758.GH23042@quack.suse.cz> Date: Thu, 24 Feb 2011 12:37:53 -0500 Message-Id: <1298566775-sup-730@think> User-Agent: Sup/git Content-Transfer-Encoding: 8bit X-Source-IP: acsmt353.oracle.com [141.146.40.153] X-Auth-Type: Internal IP X-CT-RefId: str=0001.0A090202.4D6697A6.0265:SCFMA4539814,ss=1,fgs=0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2089 Lines: 42 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. -chris -- 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/