xfstests 247: Test for race between direct I/O and mmap

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: Lachlan McIlroy <lmcilory@redhat.com>
Signed-off-by: Eric Sandeen <sandeen@redhat.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>

247

@@ -0,0 +1,80 @@
+#! /bin/bash
+# FS QA Test No. 247
+#
+# 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@redhat.com
+
+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

247.out

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+QA output created by 247
+Silence is golden.

group

@@ -360,3 +360,4 @@ deprecated
 244 auto quota quick
 245 auto quick dir
 246 auto quick rw
+247 auto quick rw