ext4: fix smatch warning in move_extent.c's mext_replace_branches()

Commit 2147b1a6a48 resulted in a new smatch warning:

> fs/ext4/move_extent.c:693 mext_replace_branches()
> 	 warn: variable dereferenced before check 'dext' (see line 683)

Fix this by adding a check to make sure dext is non-NULL before we
derefrence it.

Signed-off-by: Akria Fujita <a-fujita@rs.jp.nec.com>
[ modified by tytso to make sure an ext4_error is called ]
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

1 files changed, 4 insertions, 1 deletions

diff --git a/fs/ext4/move_extent.c b/fs/ext4/move_extent.c
index d9cc5ee42f53..e4cdb5188f34 100644
--- a/fs/ext4/move_extent.c
+++ b/fs/ext4/move_extent.c
@@ -681,6 +681,8 @@ mext_replace_branches(handle_t *handle, struct inode *orig_inode,
 
         depth = ext_depth(donor_inode);
         dext = donor_path[depth].p_ext;
+        if (unlikely(!dext))
+                goto missing_donor_extent;
         tmp_dext = *dext;
 
         *err = mext_calc_swap_extents(&tmp_dext, &tmp_oext, orig_off,
@@ -691,7 +693,8 @@ mext_replace_branches(handle_t *handle, struct inode *orig_inode,
         /* Loop for the donor extents */
         while (1) {
                 /* The extent for donor must be found. */
-                if (!dext) {
+                if (unlikely(!dext)) {
+                missing_donor_extent:
                         EXT4_ERROR_INODE(donor_inode,
                                    "The extent for donor must be found");
                         *err = -EIO;