Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755183Ab0FAKar (ORCPT ); Tue, 1 Jun 2010 06:30:47 -0400 Received: from mtagate4.uk.ibm.com ([194.196.100.164]:54121 "EHLO mtagate4.uk.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753408Ab0FAKao (ORCPT ); Tue, 1 Jun 2010 06:30:44 -0400 Date: Tue, 1 Jun 2010 12:30:42 +0200 From: Christof Schmitt To: Boaz Harrosh Cc: James Bottomley , "Martin K. Petersen" , linux-scsi@vger.kernel.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, Chris Mason Subject: Re: Wrong DIF guard tag on ext2 write Message-ID: <20100601103041.GA15922@schmichrtp.mainz.de.ibm.com> References: <20100531112817.GA16260@schmichrtp.mainz.de.ibm.com> <1275318102.2823.47.camel@mulgrave.site> <4C03D5FD.3000202@panasas.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4C03D5FD.3000202@panasas.com> User-Agent: Mutt/1.5.20 (2009-12-10) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2810 Lines: 59 On Mon, May 31, 2010 at 06:30:05PM +0300, Boaz Harrosh wrote: > On 05/31/2010 06:01 PM, James Bottomley wrote: > > On Mon, 2010-05-31 at 10:20 -0400, Martin K. Petersen wrote: > >>>>>>> "Christof" == Christof Schmitt writes: > >> > >> Christof> Since the guard tags are created in Linux, it seems that the > >> Christof> data attached to the write request changes between the > >> Christof> generation in bio_integrity_generate and the call to > >> Christof> sd_prep_fn. > >> > >> Yep, known bug. Page writeback locking is messed up for buffer_head > >> users. The extNfs folks volunteered to look into this a while back but > >> I don't think they have found the time yet. > >> > >> > >> Christof> Using ext3 or ext4 instead of ext2 does not show the problem. > >> > >> Last I looked there were still code paths in ext3 and ext4 that > >> permitted pages to be changed during flight. I guess you've just been > >> lucky. > > > > Pages have always been modifiable in flight. The OS guarantees they'll > > be rewritten, so the drivers can drop them if it detects the problem. > > This is identical to the iscsi checksum issue (iscsi adds a checksum > > because it doesn't trust TCP/IP and if the checksum is generated in > > software, there's time between generation and page transmission for the > > alteration to occur). The solution in the iscsi case was not to > > complain if the page is still marked dirty. > > > > And also why RAID1 and RAID4/5/6 need the data bounced. I wish VFS > would prevent data writing given a device queue flag that requests > it. So all these devices and modes could just flag the VFS/filesystems > that: "please don't allow concurrent writes, otherwise I need to copy data" > > From what Chris Mason has said before, all the mechanics are there, and it's > what btrfs is doing. Though I don't know how myself? I also tested with btrfs and invalid guard tags in writes have been encountered as well (again in 2.6.34). The only difference is that no error was reported to userspace, although this might be a configuration issue. What is the best strategy to continue with the invalid guard tags on write requests? Should this be fixed in the filesystems? Another idea would be to pass invalid guard tags on write requests down to the hardware, expect an "invalid guard tag" error and report it to the block layer where a new checksum is generated and the request is issued again. Basically implement a retry through the whole I/O stack. But this also sounds complicated. -- Christof Schmitt -- 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/