btrfs: fix btrfs_cont_expand() freeing IS_ERR em

btrfs_cont_expand() tries to free an IS_ERR em as it gets an error from
btrfs_get_extent() and breaks out of its loop.

An instance of -EEXIST was reported in the wild:

  https://bugzilla.redhat.com/show_bug.cgi?id=874407

I have no idea if that -EEXIST is surprising, or not.  Regardless, this
error handling should be cleaned up to handle other reasonable errors
(ENOMEM, EIO; whatever).

This seemed to be the only buggy freeing of the relatively rare IS_ERR
em so I opted to fix the caller rather than teach free_extent_map() to
use IS_ERR_OR_NULL().

Signed-off-by: Zach Brown <zab@redhat.com>
Reviewed-by: Eric Sandeen <sandeen@redhat.com>
Signed-off-by: Josef Bacik <josef@toxicpanda.com>

1 files changed, 1 insertions, 0 deletions

diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index ac98384b174e..3d2c64d4734a 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -3677,6 +3677,7 @@ int btrfs_cont_expand(struct inode *inode, loff_t oldsize, loff_t size)
                                 block_end - cur_offset, 0);
                 if (IS_ERR(em)) {
                         err = PTR_ERR(em);
+                        em = NULL;
                         break;
                 }
                 last_byte = min(extent_map_end(em), block_end);