From mboxrd@z Thu Jan 1 00:00:00 1970 From: Eric Sandeen Subject: [PATCH/RFC] pass dio_complete proper offset from finished_one_bio Date: Sat, 25 Nov 2006 22:25:55 -0600 Message-ID: <45691753.60500@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: rtc@gmx.de Return-path: Received: from mx1.redhat.com ([66.187.233.31]:22991 "EHLO mx1.redhat.com") by vger.kernel.org with ESMTP id S934286AbWKZE0C (ORCPT ); Sat, 25 Nov 2006 23:26:02 -0500 To: linux-fsdevel@vger.kernel.org, linux-kernel@vger.org, xfs@oss.sgi.com Sender: linux-fsdevel-owner@vger.kernel.org List-Id: linux-fsdevel.vger.kernel.org We saw problems w/ xfs doing AIO+DIO into a sparse file. https://bugzilla.redhat.com/bugzilla/show_bug.cgi?id=217098 It seemed that xfs was doing "extent conversion" at the wrong offsets, so written regions came up as unwritten (zeros) and stale data was exposed in the region after the write. Thanks to Peter Backes for the very nice testcase. This also broke xen with blktap over xfs. Here's what I found: finished_one_bio calls dio_complete calls xfs_end_io_direct with an offset, but: offset = dio->iocb->ki_pos; so this is the -current- post-IO position, not the IO start point that dio_complete expects. So, xfs converts the the wrong region. Ouch! XFS seems to be the only filesystem that uses the offset passed to the end_io function, so only it is affected by this as near as I can tell. However, the "short read" case is probably also wrong, as it is checking: if ((dio->rw == READ) && ((offset + transferred) > dio->i_size)) transferred = dio->i_size - offset; but offset is the ending IO position in this case too. This patch seems to fix it up. Comments? Thanks, -Eric Signed-off-by: Eric Sandeen Index: linux-2.6.18/fs/direct-io.c =================================================================== --- linux-2.6.18.orig/fs/direct-io.c +++ linux-2.6.18/fs/direct-io.c @@ -244,12 +244,12 @@ static void finished_one_bio(struct dio */ spin_unlock_irqrestore(&dio->bio_lock, flags); - /* Check for short read case */ transferred = dio->result; - offset = dio->iocb->ki_pos; + offset = dio->iocb->ki_pos - transferred; + /* Check for short read case */ if ((dio->rw == READ) && - ((offset + transferred) > dio->i_size)) + (dio->iocb->ki_pos > dio->i_size)) transferred = dio->i_size - offset; /* check for error in completion path */