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

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Subject: [PATCH] xfstests 246: Test for race between direct I/O and mmap
From: Eric Sandeen <sandeen@xxxxxxxxxx>
Date: Fri, 12 Nov 2010 16:37:07 -0600
Cc: Lachlan McIlroy <lmcilroy@xxxxxxxxxx>
User-agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.2.9) Gecko/20100907 Fedora/3.1.3-1.fc13 Lightning/1.0b3pre Thunderbird/3.1.3

From: Lachlan McIlroy <lmcilory@xxxxxxxxxx>

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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