Btrfs: update fix for read corruption of compressed and shared extents
My previous fix in commit 005efedf2c7d ("Btrfs: fix read corruption of
compressed and shared extents") was effective only if the compressed
extents cover a file range with a length that is not a multiple of 16
pages. That's because the detection of when we reached a different range
of the file that shares the same compressed extent as the previously
processed range was done at extent_io.c:__do_contiguous_readpages(),
which covers subranges with a length up to 16 pages, because
extent_readpages() groups the pages in clusters no larger than 16 pages.
So fix this by tracking the start of the previously processed file
range's extent map at extent_readpages().
The following test case for fstests reproduces the issue:
seq=`basename $0`
seqres=$RESULT_DIR/$seq
echo "QA output created by $seq"
tmp=/tmp/$$
status=1 # failure is the default!
trap "_cleanup; exit \$status" 0 1 2 3 15
_cleanup()
{
rm -f $tmp.*
}
# get standard environment, filters and checks
. ./common/rc
. ./common/filter
# real QA test starts here
_need_to_be_root
_supported_fs btrfs
_supported_os Linux
_require_scratch
_require_cloner
rm -f $seqres.full
test_clone_and_read_compressed_extent()
{
local mount_opts=$1
_scratch_mkfs >>$seqres.full 2>&1
_scratch_mount $mount_opts
# Create our test file with a single extent of 64Kb that is going to
# be compressed no matter which compression algo is used (zlib/lzo).
$XFS_IO_PROG -f -c "pwrite -S 0xaa 0K 64K" \
$SCRATCH_MNT/foo | _filter_xfs_io
# Now clone the compressed extent into an adjacent file offset.
$CLONER_PROG -s 0 -d $((64 * 1024)) -l $((64 * 1024)) \
$SCRATCH_MNT/foo $SCRATCH_MNT/foo
echo "File digest before unmount:"
md5sum $SCRATCH_MNT/foo | _filter_scratch
# Remount the fs or clear the page cache to trigger the bug in
# btrfs. Because the extent has an uncompressed length that is a
# multiple of 16 pages, all the pages belonging to the second range
# of the file (64K to 128K), which points to the same extent as the
# first range (0K to 64K), had their contents full of zeroes instead
# of the byte 0xaa. This was a bug exclusively in the read path of
# compressed extents, the correct data was stored on disk, btrfs
# just failed to fill in the pages correctly.
_scratch_remount
echo "File digest after remount:"
# Must match the digest we got before.
md5sum $SCRATCH_MNT/foo | _filter_scratch
}
echo -e "\nTesting with zlib compression..."
test_clone_and_read_compressed_extent "-o compress=zlib"
_scratch_unmount
echo -e "\nTesting with lzo compression..."
test_clone_and_read_compressed_extent "-o compress=lzo"
status=0
exit
Cc: stable@vger.kernel.org
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Tested-by: Timofey Titovets <nefelim4ag@gmail.com>
diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
index 11aa8f7..363726b 100644
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -3144,12 +3144,12 @@
get_extent_t *get_extent,
struct extent_map **em_cached,
struct bio **bio, int mirror_num,
- unsigned long *bio_flags, int rw)
+ unsigned long *bio_flags, int rw,
+ u64 *prev_em_start)
{
struct inode *inode;
struct btrfs_ordered_extent *ordered;
int index;
- u64 prev_em_start = (u64)-1;
inode = pages[0]->mapping->host;
while (1) {
@@ -3165,7 +3165,7 @@
for (index = 0; index < nr_pages; index++) {
__do_readpage(tree, pages[index], get_extent, em_cached, bio,
- mirror_num, bio_flags, rw, &prev_em_start);
+ mirror_num, bio_flags, rw, prev_em_start);
page_cache_release(pages[index]);
}
}
@@ -3175,7 +3175,8 @@
int nr_pages, get_extent_t *get_extent,
struct extent_map **em_cached,
struct bio **bio, int mirror_num,
- unsigned long *bio_flags, int rw)
+ unsigned long *bio_flags, int rw,
+ u64 *prev_em_start)
{
u64 start = 0;
u64 end = 0;
@@ -3196,7 +3197,7 @@
index - first_index, start,
end, get_extent, em_cached,
bio, mirror_num, bio_flags,
- rw);
+ rw, prev_em_start);
start = page_start;
end = start + PAGE_CACHE_SIZE - 1;
first_index = index;
@@ -3207,7 +3208,8 @@
__do_contiguous_readpages(tree, &pages[first_index],
index - first_index, start,
end, get_extent, em_cached, bio,
- mirror_num, bio_flags, rw);
+ mirror_num, bio_flags, rw,
+ prev_em_start);
}
static int __extent_read_full_page(struct extent_io_tree *tree,
@@ -4218,6 +4220,7 @@
struct page *page;
struct extent_map *em_cached = NULL;
int nr = 0;
+ u64 prev_em_start = (u64)-1;
for (page_idx = 0; page_idx < nr_pages; page_idx++) {
page = list_entry(pages->prev, struct page, lru);
@@ -4234,12 +4237,12 @@
if (nr < ARRAY_SIZE(pagepool))
continue;
__extent_readpages(tree, pagepool, nr, get_extent, &em_cached,
- &bio, 0, &bio_flags, READ);
+ &bio, 0, &bio_flags, READ, &prev_em_start);
nr = 0;
}
if (nr)
__extent_readpages(tree, pagepool, nr, get_extent, &em_cached,
- &bio, 0, &bio_flags, READ);
+ &bio, 0, &bio_flags, READ, &prev_em_start);
if (em_cached)
free_extent_map(em_cached);