Commit d4e20494 authored by Qu Wenruo's avatar Qu Wenruo Committed by David Sterba
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btrfs: qgroup: Fix reserved data space leak if we have multiple reserve calls

The following script can cause btrfs qgroup data space leak:

  mkfs.btrfs -f $dev
  mount $dev -o nospace_cache $mnt

  btrfs subv create $mnt/subv
  btrfs quota en $mnt
  btrfs quota rescan -w $mnt
  btrfs qgroup limit 128m $mnt/subv

  for (( i = 0; i < 3; i++)); do
          # Create 3 64M holes for latter fallocate to fail
          truncate -s 192m $mnt/subv/file
          xfs_io -c "pwrite 64m 4k" $mnt/subv/file > /dev/null
          xfs_io -c "pwrite 128m 4k" $mnt/subv/file > /dev/null

          # it's supposed to fail, and each failure will leak at least 64M
          # data space
          xfs_io -f -c "falloc 0 192m" $mnt/subv/file &> /dev/null
          rm $mnt/subv/file

  # Shouldn't fail after we removed the file
  xfs_io -f -c "falloc 0 64m" $mnt/subv/file

Btrfs qgroup data reserve code allow multiple reservations to happen on
a single extent_changeset:
	btrfs_qgroup_reserve_data(inode, &data_reserved, 0, SZ_1M);
	btrfs_qgroup_reserve_data(inode, &data_reserved, SZ_1M, SZ_2M);
	btrfs_qgroup_reserve_data(inode, &data_reserved, 0, SZ_4M);

Btrfs qgroup code has its internal tracking to make sure we don't
double-reserve in above example.

The only pattern utilizing this feature is in the main while loop of
btrfs_fallocate() function.

However btrfs_qgroup_reserve_data()'s error handling has a bug in that
on error it clears all ranges in the io_tree with EXTENT_QGROUP_RESERVED
flag but doesn't free previously reserved bytes.

This bug has a two fold effect:
  This is the correct behavior, but it prevents
  btrfs_qgroup_check_reserved_leak() to catch the leakage as the
  detector is purely EXTENT_QGROUP_RESERVED flag based.

- Leak the previously reserved data bytes.

The bug manifests when N calls to btrfs_qgroup_reserve_data are made and
the last one fails, leaking space reserved in the previous ones.

Also free previously reserved data bytes when btrfs_qgroup_reserve_data

Fixes: 52472553

 ("btrfs: qgroup: Introduce btrfs_qgroup_reserve_data function")
CC: # 4.4+
Signed-off-by: default avatarQu Wenruo <>
Signed-off-by: default avatarDavid Sterba <>
parent bab32fc0
......@@ -3442,6 +3442,9 @@ cleanup:
while ((unode = ulist_next(&reserved->range_changed, &uiter)))
clear_extent_bit(&BTRFS_I(inode)->io_tree, unode->val,
unode->aux, EXTENT_QGROUP_RESERVED, 0, 0, NULL);
/* Also free data bytes of already reserved one */
btrfs_qgroup_free_refroot(root->fs_info, root->root_key.objectid,
orig_reserved, BTRFS_QGROUP_RSV_DATA);
return ret;
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