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>

1 files changed, 11 insertions, 8 deletions

diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
index 11aa8f743b90..363726b08a51 100644
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -3144,12 +3144,12 @@ static inline void __do_contiguous_readpages(struct extent_io_tree *tree,
                                              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 @@ static inline void __do_contiguous_readpages(struct extent_io_tree *tree,
 
         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 @@ static void __extent_readpages(struct extent_io_tree *tree,
                                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 @@ static void __extent_readpages(struct extent_io_tree *tree,
                                                   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 @@ static void __extent_readpages(struct extent_io_tree *tree,
                 __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 @@ int extent_readpages(struct extent_io_tree *tree,
         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 @@ int extent_readpages(struct extent_io_tree *tree,
                 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);