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 11aa8f743b9041b1baa1414c6f310a02d7d60a42..363726b08a51e6f23ba984985fd7aaef2cfac1c2 100644 (file)
--- 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);