From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx2.suse.de ([195.135.220.15]:42606 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1762366AbdEWIur (ORCPT ); Tue, 23 May 2017 04:50:47 -0400 Date: Tue, 23 May 2017 10:50:44 +0200 From: Jan Kara Subject: Re: [PATCH 2/3] xfs: Fix off-by-in in loop termination in xfs_find_get_desired_pgoff() Message-ID: <20170523085044.GA1119@quack2.suse.cz> References: <20170518104850.14508-1-jack@suse.cz> <20170518104850.14508-3-jack@suse.cz> <20170522175045.GB1473@bfoster.bfoster> <20170523032123.GW7250@eguan.usersys.redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170523032123.GW7250@eguan.usersys.redhat.com> Sender: linux-xfs-owner@vger.kernel.org List-ID: List-Id: xfs To: Eryu Guan Cc: Brian Foster , Jan Kara , "Darrick J. Wong" , linux-xfs@vger.kernel.org On Tue 23-05-17 11:21:23, Eryu Guan wrote: > On Mon, May 22, 2017 at 01:50:47PM -0400, Brian Foster wrote: > > On Thu, May 18, 2017 at 12:48:49PM +0200, Jan Kara wrote: > > > There is an off-by-one error in loop termination conditions in > > > xfs_find_get_desired_pgoff() since 'end' may index a page beyond end of > > > desired range if 'endoff' is page aligned. It doesn't have any visible > > > effects but still it is good to fix it. > > > > > > Signed-off-by: Jan Kara > > > --- > > > fs/xfs/xfs_file.c | 2 +- > > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > > > diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c > > > index f371812e20c6..3714b5736fd3 100644 > > > --- a/fs/xfs/xfs_file.c > > > +++ b/fs/xfs/xfs_file.c > > > @@ -1043,7 +1043,7 @@ xfs_find_get_desired_pgoff( > > > > > > index = startoff >> PAGE_SHIFT; > > > endoff = XFS_FSB_TO_B(mp, map->br_startoff + map->br_blockcount); > > > - end = endoff >> PAGE_SHIFT; > > > + end = (endoff - 1) >> PAGE_SHIFT; > > > > Hmm.. I think this messes with the want count for the pagevec_lookup(). > > E.g.: > > > > # xfs_io -fc "truncate 0" -c "falloc 0 16k" -c "pwrite 0 16k" -c "seek -h 0" /mnt/file > > wrote 16384/16384 bytes at offset 0 > > 16 KiB, 4 ops; 0.0000 sec (200.321 MiB/sec and 51282.0513 ops/sec) > > Whence Result > > HOLE 12288 > > I think the root cause is that the calculation for 'want' is wrong, it > has an off-by-one bug too. I sent a patch[1] to fix it, with my patch > applied on top of Jan's patchset, your test case passed (report HOLE at > 16k). Can you please take a look if it's a correct fix? Thanks! Yes, I've messed that up. It is a bug introduced by my series as Brian properly noticed. Thanks guys for noticing and fixing it! Darrick, should I fold in Eryu's fix and send v4 of the series or will you just pick up Eryu's fix? Honza -- Jan Kara SUSE Labs, CR