[PATCH 2/2] generic/352: new case test mmaped data when blocksize less than pagesize

[Zorro Lang <zlang@redhat.com>]

This case is a regression test for linux commit 90a80202:

  vfs: fix data corruption when blocksize < pagesize for mmaped data

  ->page_mkwrite() is used by filesystems to allocate blocks under a page
  which is becoming writeably mmapped in some process' address space. This
  allows a filesystem to return a page fault if there is not enough space
  available, user exceeds quota or similar problem happens, rather than
  silently discarding data later when writepage is called.

  However VFS fails to call ->page_mkwrite() in all the cases where
  filesystems need it when blocksize < pagesize. For example when
  blocksize = 1024, pagesize = 4096 the following is problematic:
    ftruncate(fd, 0);
    pwrite(fd, buf, 1024, 0);
    map = mmap(NULL, 1024, PROT_WRITE, MAP_SHARED, fd, 0);
    map[0] = 'a';       ----> page_mkwrite() for index 0 is called
    ftruncate(fd, 10000); /* or even pwrite(fd, buf, 1, 10000) */
    mremap(map, 1024, 10000, 0);
    map[4095] = 'a';    ----> no page_mkwrite() called

  At the moment ->page_mkwrite() is called, filesystem can allocate only
  one block for the page because i_size == 1024. Otherwise it would create
  blocks beyond i_size which is generally undesirable. But later at
  ->writepage() time, we also need to store data at offset 4095 but we
  don't have block allocated for it.

  This patch introduces a helper function filesystems can use to have
  ->page_mkwrite() called at all the necessary moments.

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

Hi,

After xfsprogs merged commit:
  e0a8808 xfs_io: allow mmap command to reserve some free space

We can reserve(not 100% sure, but pretty high rate) some memory for mremap
extend the map space. Due to it, I can use xfs_io to implement this
case.

There're 2 problems when I write this case:
1. The reserved memory space can't be kept 100%, especially when
system run heavy memory load. But I think it hard to resolve.

2. When xfs_io process be killed by SIGBUS, I can't catch the "Bus error"
output(it not on stdout/stderr). But it will printed into .out file. So
I use a pipe stop it(Generally, that _filter_xfs_io after the pipe is
useless. I just need a pipe.). But I'm not sure if it's a good idea.
Anyone have better idea?

(BTW, this case rely on my last patch about _require_xfs_io_command.)

Thanks,
Zorro

 tests/generic/352     | 109 ++++++++++++++++++++++++++++++++++++++++++++++++++
 tests/generic/352.out |   3 ++
 tests/generic/group   |   1 +
 3 files changed, 113 insertions(+)
 create mode 100755 tests/generic/352
 create mode 100644 tests/generic/352.out

diff --git a/tests/generic/352 b/tests/generic/352
new file mode 100755
index 0000000..5e69127
--- /dev/null
+++ b/tests/generic/352
@@ -0,0 +1,109 @@
+#! /bin/bash
+# FS QA Test 352
+#
+# Regression test for linux commit 90a80202, data corruption when
+# blocksize < pagesize for mmaped data.
+#
+#-----------------------------------------------------------------------
+# Copyright (c) 2016 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
+
+# support fs which can make block size < page size
+_supported_fs xfs ext2 ext3 ext4 ext4dev udf
+_supported_os Linux
+_require_scratch
+_require_xfs_io_command mmap "-s <size>"
+_require_xfs_io_command mremap
+_require_xfs_io_command truncate
+_require_xfs_io_command pwrite
+_require_xfs_io_command mwrite
+
+sector_size=`blockdev --getss $SCRATCH_DEV`
+page_size=$(get_page_size)
+block_size=$((page_size/2))
+
+if [ $sector_size -gt $block_size ];then
+    _notrun "need sector size < page size"
+fi
+
+unset MKFS_OPTIONS
+# For save time, 512MiB is enough to reproduce bug
+_scratch_mkfs_sized 536870912 $block_size >$seqres.full 2>&1
+
+# avoid the interference of XFS preallocation
+if [ "$FSTYP" = xfs ];then
+    MOUNT_OPTIONS="$MOUNT_OPTIONS -o allocsize=$page_size"
+fi
+_scratch_mount
+
+# take one block size space
+dd if=/dev/zero of=$SCRATCH_MNT/testfile bs=$block_size count=1 >$seqres.full 2>&1
+# fill all free space
+dd if=/dev/zero of=$SCRATCH_MNT/full bs=$block_size >$seqres.full 2>&1
+sync
+
+# truncate 0
+# pwrite -S 0x61 0 $block_size
+# mmap -rw -s $((page_size * 2)) 0 $block_size
+# mwrite -S 0x61 0 1  --> page_mkwrite() for index 0 is called
+# truncate $((page_size * 2))
+# mremap $((page_size * 2))
+# mwrite -S 0x61 $((page_size - 1)) 1  --> [bug] no page_mkwrite() called
+#
+# If there's a bug, the last step will be killed by SIGBUS, and it won't
+# write a "0x61" on the disk.
+#
+# Note: mremap maybe failed when memory load is heavy. 
+$XFS_IO_PROG -f \
+	     -c "truncate 0" \
+	     -c "pwrite -S 0x61 0 $block_size" \
+	     -c "mmap -rw -s $((page_size * 2)) 0 $block_size" \
+	     -c "mwrite -S 0x61 0 1" \
+	     -c "truncate $((page_size * 2))" \
+	     -c "mremap $((page_size * 2))" \
+	     -c "mwrite -S 0x61 $((page_size - 1)) 1" \
+	     $SCRATCH_MNT/testfile | _filter_xfs_io
+
+# we will see 0x61 written by "mwrite -S 0x61 0 1"
+# we shouldn't see one more 0x61 by the last mwrite.
+hexdump -e '1/1 "%02x "' $SCRATCH_MNT/testfile
+
+# success, all done
+status=0
+exit
diff --git a/tests/generic/352.out b/tests/generic/352.out
new file mode 100644
index 0000000..8be005d
--- /dev/null
+++ b/tests/generic/352.out
@@ -0,0 +1,3 @@
+QA output created by 352
+61 *
+00 *
diff --git a/tests/generic/group b/tests/generic/group
index 36fb759..7a72f6b 100644
--- a/tests/generic/group
+++ b/tests/generic/group
@@ -354,3 +354,4 @@
 349 blockdev quick rw
 350 blockdev quick rw
 351 blockdev quick rw
+352 auto quick
-- 
2.5.5