Patch "Btrfs: update fix for read corruption of compressed and shared extents" has been added to the 3.14-stable tree

This is a note to let you know that I've just added the patch titled

Btrfs: update fix for read corruption of compressed and shared extents

to the 3.14-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
btrfs-update-fix-for-read-corruption-of-compressed-and-shared-extents.patch
and it can be found in the queue-3.14 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Filipe Manana <[email protected]>
Date: Mon, 28 Sep 2015 09:56:26 +0100
Subject: Btrfs: update fix for read corruption of compressed and shared extents

From: Filipe Manana <[email protected]>

commit 808f80b46790f27e145c72112189d6a3be2bc884 upstream.

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

---
 fs/btrfs/extent_io.c |   19 +++++++++++--------
 1 file changed, 11 insertions(+), 8 deletions(-)

@@ -3012,12 +3012,12 @@ static inline void __do_contiguous_readp
 					     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) {

@@ -3033,7 +3033,7 @@ static inline void __do_contiguous_readp
 
 	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]);
 	}
 }

@@ -3043,7 +3043,8 @@ static void __extent_readpages(struct ex
 			       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;

@@ -3064,7 +3065,7 @@ static void __extent_readpages(struct ex
 						  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;

@@ -3075,7 +3076,8 @@ static void __extent_readpages(struct ex
 		__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,

@@ -3967,6 +3969,7 @@ int extent_readpages(struct extent_io_tr
 	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);

@@ -3983,12 +3986,12 @@ int extent_readpages(struct extent_io_tr
 		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);

Patches currently in stable-queue which might be from [email protected] are

queue-3.14/btrfs-fix-read-corruption-of-compressed-and-shared-extents.patch queue-3.14/btrfs-update-fix-for-read-corruption-of-compressed-and-shared-extents.patch queue-3.14/btrfs-skip-waiting-on-ordered-range-for-special-files.patch