Btrfs: fix inode eviction infinite loop after extent_same ioctl

fdmanana · masoncl · commit 113e8283869b · 2015-04-13T07:03:27.000-07:00
If we pass a length of 0 to the extent_same ioctl, we end up locking an
extent range with a start offset greater then its end offset (if the
destination file's offset is greater than zero). This results in a warning
from extent_io.c:insert_state through the following call chain:

  btrfs_extent_same()
    btrfs_double_lock()
      lock_extent_range()
        lock_extent(inode-&gt;io_tree, offset, offset + len - 1)
          lock_extent_bits()
            __set_extent_bit()
              insert_state()
                --&gt; WARN_ON(end &lt; start)

This leads to an infinite loop when evicting the inode. This is the same
problem that my previous patch titled
"Btrfs: fix inode eviction infinite loop after cloning into it" addressed
but for the extent_same ioctl instead of the clone ioctl.

CC: &lt;stable@vger.kernel.org&gt;
Signed-off-by: Filipe Manana &lt;fdmanana@suse.com&gt;
Reviewed-by: Omar Sandoval &lt;osandov@osandov.com&gt;
Signed-off-by: Chris Mason &lt;clm@fb.com&gt;
diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
@@ -2897,6 +2897,9 @@ static int btrfs_extent_same(struct inode *src, u64 loff, u64 len,
 	if (src == dst)
 		return -EINVAL;
 
+	if (len == 0)
+		return 0;
+
 	btrfs_double_lock(src, loff, dst, dst_loff, len);
 
 	ret = extent_same_check_offsets(src, loff, len);
