[PATCH] generic: test eofblocks race with file extending aio dio writes

[Zorro Lang <zlang@redhat.com>]

It's possible for post-eof blocks to end up being used for direct I/O
writes. dio write performs an upfront unwritten extent allocation, sends
the dio and then updates the inode size (if necessary) on write
completion. If a file release occurs while a file extending dio write is
in flight, it is possible to mistake the post-eof blocks for speculative
preallocation and incorrectly truncate them from the inode. This means
that the resulting dio write completion can discover a hole and allocate
new blocks rather than perform unwritten extent conversion.

A kernel warning can be reproduced by generic/299 on XFS:
  XFS: Assertion failed: tp->t_blk_res_used <= tp->t_blk_res, \
       file: fs/xfs//xfs_trans.c, line: 309

The root cause is that xfs_free_eofblocks() uses i_size to truncate
post-eof blocks from the inode, but async, file extending direct writes
do not update i_size until write completion, long after inode locks are
dropped. Therefore, xfs_free_eofblocks() effectively truncates the inode
to the incorrect size.

For cover this filesystem corruption testing, write this new case to
check data integrality manually, not only depend on a kernel warning.

Signed-off-by: Zorro Lang <zlang@redhat.com>
---

Hi,

This case is similar with generic/114 which use same aio-dio-eof-race.c
program. I was planning to write an aio writer, but I found there's
already a good program written by Eric, so I turn to use it directly :)

This case is different with g/114, this case runs aio-dio-eof-race
with an "open & close" process together. This multi-processes
maybe trigger a free_eofblocks race with file extending dio write.

Thanks,
Zorro


 tests/generic/426     | 87 +++++++++++++++++++++++++++++++++++++++++++++++++++
 tests/generic/426.out |  2 ++
 tests/generic/group   |  1 +
 3 files changed, 90 insertions(+)
 create mode 100755 tests/generic/426
 create mode 100644 tests/generic/426.out

diff --git a/tests/generic/426 b/tests/generic/426
new file mode 100755
index 0000000..ff022ad
--- /dev/null
+++ b/tests/generic/426
@@ -0,0 +1,87 @@
+#! /bin/bash
+# FS QA Test 426
+#
+# Try to trigger a race of free eofblocks and file extending dio writes.
+# A known bug of XFS has been fixed by "e4229d6 xfs: fix eofblocks race
+# with file extending async dio writes"
+#
+#-----------------------------------------------------------------------
+# Copyright (c) 2017 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
+#-----------------------------------------------------------------------
+#
+
+seq=`basename $0`
+seqres=$RESULT_DIR/$seq
+echo "QA output created by $seq"
+
+here=`pwd`
+tmp=/tmp/$$
+status=1	# failure is the default!
+trap "_cleanup; exit \$status" 0 1 2 3 15
+
+_cleanup()
+{
+	cd /
+	rm -f $tmp.*
+}
+
+# get standard environment, filters and checks
+. ./common/rc
+. ./common/filter
+
+# remove previous $seqres.full before test
+rm -f $seqres.full
+
+# real QA test starts here
+
+# Modify as appropriate.
+_supported_fs generic
+_supported_os Linux
+_require_scratch
+_require_aiodio aio-dio-eof-race
+
+# limit the filesystem size, to save the time of filling filesystem
+_scratch_mkfs_sized $((1024 * 1024 * 1024)) >>$seqres.full 2>&1
+_scratch_mount
+
+# try to write more bytes than filesystem size to fill the filesystem
+$XFS_IO_PROG -f -c "pwrite -S 0x55 0 $((1024 * 1024 * 1024 * 2))" \
+	     $SCRATCH_MNT/fillfs-$seq 2>/dev/null
+rm -f $SCRATCH_MNT/fillfs-$seq
+
+# start a background aio writer, which does several extending loops
+# internally and check data integrality
+$AIO_TEST $SCRATCH_MNT/tst-aio-dio-eof-race.$seq &
+aio_pid=$!
+
+# open & close the file frequently, to trigger xfs_free_eofblocks
+while true; do
+	cat $SCRATCH_MNT/tst-aio-dio-eof-race.$seq >/dev/null 2>&1
+done &
+open_close_pid=$!
+
+wait $aio_pid
+status=$?
+kill $open_close_pid
+wait $open_close_pid
+if [ $status -ne 0 ]; then
+	od -t x1 $SCRATCH_MNT/tst-aio-dio-eof-race.$seq >> $seqres.full
+	exit
+fi
+
+# success, all done
+status=0
+exit
diff --git a/tests/generic/426.out b/tests/generic/426.out
new file mode 100644
index 0000000..ad7a01a
--- /dev/null
+++ b/tests/generic/426.out
@@ -0,0 +1,2 @@
+QA output created by 426
+Success, all done.
diff --git a/tests/generic/group b/tests/generic/group
index 6d6e4f6..70c36f9 100644
--- a/tests/generic/group
+++ b/tests/generic/group
@@ -428,3 +428,4 @@
 423 auto quick
 424 auto quick
 425 auto quick attr
+426 auto aio rw
-- 
2.7.4