From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from cuda.sgi.com (cuda3.sgi.com [192.48.176.15]) by oss.sgi.com (8.14.3/8.14.3/SuSE Linux 0.8) with ESMTP id q58NDOG4014527 for ; Fri, 8 Jun 2012 18:13:24 -0500 Received: from ipmail06.adl2.internode.on.net (ipmail06.adl2.internode.on.net [150.101.137.129]) by cuda.sgi.com with ESMTP id rkBcmZa0mJzRFEw3 for ; Fri, 08 Jun 2012 16:13:22 -0700 (PDT) Date: Sat, 9 Jun 2012 09:13:20 +1000 From: Dave Chinner Subject: Re: [PATCH] xfs: xfs_vm_writepage clear iomap_valid when !buffer_uptodate (REV2) Message-ID: <20120608231320.GZ22848@dastard> References: <20120601192207.D6DE99F997@arenaud-laptop> <20120605114516.GM4347@dastard> <4FCDFCE5.5020702@sgi.com> <4FD253D6.9060909@sgi.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <4FD253D6.9060909@sgi.com> List-Id: XFS Filesystem from SGI List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: xfs-bounces@oss.sgi.com Errors-To: xfs-bounces@oss.sgi.com To: Alain Renaud Cc: xfs@oss.sgi.com On Fri, Jun 08, 2012 at 03:34:46PM -0400, Alain Renaud wrote: > > On filesytems with a block size smaller than PAGE_SIZE we currently have > a problem with unwritten extents. If a we have multi-block page for > which an unwritten extent has been allocated, and only some of the > buffers have been written to, and they are not contiguous, we can expose > stale data from disk in the blocks between the writes after extent > conversion. > > Example of a page with unwritten and real data. > buffer content > 0 empty b_state = 0 > 1 DATA b_state = 0x1023 Uptodate,Dirty,Mapped,Unwritten > 2 DATA b_state = 0x1023 Uptodate,Dirty,Mapped,Unwritten > 3 empty b_state = 0 > 4 empty b_state = 0 > 5 DATA b_state = 0x1023 Uptodate,Dirty,Mapped,Unwritten > 6 DATA b_state = 0x1023 Uptodate,Dirty,Mapped,Unwritten > 7 empty b_state = 0 > > Buffers 1, 2, 5, and 6 have been written to, leaving 0, 3, 4, and 7 empty. > Currently buffers 1, 2, 5, and 6 are added to a single ioend, and when IO has > completed, extent conversion creates a real extent from block 1 through block > 6, leaving 0 and 7 unwritten. However buffers 3 and 4 were not written to > disk, so stale data is exposed from those blocks on a subsequent read. > > Fix this by setting iomap_valid = 0 when we find a buffer that is not > Uptodate. This ensures that buffers 5 and 6 are not added to the same > ioend as buffers 1 and 2. Later these blocks will be converted into two > separate real extents, leaving the blocks in between unwritten. > > Signed-off-by: Alain Renaud Looks good. Reviewed-by: Dave Chinner -- Dave Chinner david@fromorbit.com _______________________________________________ xfs mailing list xfs@oss.sgi.com http://oss.sgi.com/mailman/listinfo/xfs