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Re: [PATCH] xfstests 246: Test for race between direct I/O and mmap

To: Eric Sandeen <sandeen@xxxxxxxxxx>
Subject: Re: [PATCH] xfstests 246: Test for race between direct I/O and mmap
From: Lachlan McIlroy <lmcilroy@xxxxxxxxxx>
Date: Sun, 14 Nov 2010 20:01:39 -0500 (EST)
Cc: xfs mailing list <xfs@xxxxxxxxxxx>
In-reply-to: <4CDDC193.9030208@xxxxxxxxxx>
Reply-to: Lachlan McIlroy <lmcilroy@xxxxxxxxxx>
----- "Eric Sandeen" <sandeen@xxxxxxxxxx> wrote:

> From: Lachlan McIlroy <lmcilory@xxxxxxxxxx>
lmcilroy - although I was briefly known as lmcilory due a HR error.

Eric, the test looks good to me, thanks for fixing the errors in it.

> 
> A customer reported a problem:
> 
> If a process is using mmap to write to a file on an 
> ext4 filesystem while another process is using direct 
> I/O to write to the same file the first thread may 
> receive a SIGBUS during a page fault.
> 
> A SIGBUS occurs if the page fault tries to access a 
> page that is entirely beyond the end of the file but 
> in this test case that should not be happening.
> 
> Signed-off-by: Eric Sandeen <sandeen@xxxxxxxxxx>
> ---
> 
> #! /bin/bash
> # FS QA Test No. 246
> #
> # Test for race between direct I/O and mmap
> #
> #-----------------------------------------------------------------------
> # Copyright (c) 2010 Red Hat, Inc.  All Rights Reserved.
> #
> # This program is free software; you can redistribute it and/or
> # modify it under the terms of the GNU General Public License as
> # published by the Free Software Foundation.
> #
> # This program is distributed in the hope that it would be useful,
> # but WITHOUT ANY WARRANTY; without even the implied warranty of
> # MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> # GNU General Public License for more details.
> #
> # You should have received a copy of the GNU General Public License
> # along with this program; if not, write the Free Software
> Foundation,
> # Inc.,  51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
> #-----------------------------------------------------------------------
> #
> # creator
> owner=lmcilroy@xxxxxxxxxx
> 
> seq=`basename $0`
> echo "QA output created by $seq"
> 
> here=`pwd`
> tmp=/tmp/$$
> status=1      # failure is the default!
> trap "_cleanup; exit \$status" 0 1 2 3 7 15
> 
> _cleanup()
> {
>     cd /
>     rm -f $tmp.* $testfile
>     wait
> }
> 
> # get standard environment, filters and checks
> . ./common.rc
> . ./common.filter
> 
> # real QA test starts here
> 
> # Modify as appropriate.
> _supported_fs generic
> _supported_os Linux
> 
> testfile=$TEST_DIR/$seq.$$
> 
> loops=500
> iosize=1048576
> 
> # Initialise file
> dd if=/dev/zero of=$testfile bs=$iosize count=$loops &> /dev/null
> [ $? -ne 0 ] && exit
> sync
>       
> # Direct I/O overwriter
> dd if=/dev/zero of=$testfile oflag=direct bs=$iosize count=$loops
> conv=notrunc &> /dev/null &
> [ $? -ne 0 ] && exit
> 
> # Mmap writer
> start=`expr $loops - 1`
> for i in `seq $start -1 0`
> do
>       offset=`expr $i \* $iosize`
>       $XFS_IO_PROG -F -f -c "mmap -w $offset $iosize" -c "mwrite $offset
> $iosize" $testfile
>       [ $? -ne 0 ] && exit
> done
> 
> wait
> 
> echo "Silence is golden."
> 
> # success, all done
> status=0
> exit

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