Btrfs: avoid null deref in unpin_extent_cache()

I re-orderred the checks to avoid dereferencing "em" if it was null.

Found by smatch static checker.

Signed-off-by: Dan Carpenter <error27@gmail.com>
Signed-off-by: Chris Mason <chris.mason@oracle.com>

diff --git a/fs/btrfs/extent_map.c b/fs/btrfs/extent_map.c
index 2c726b7b9faa17af725b8a5b8319148758b7dd91..ccbdcb54ec5d988f39690b33f9964c35da134e30 100644 (file)
--- a/fs/btrfs/extent_map.c
+++ b/fs/btrfs/extent_map.c
@@ -208,7 +208,7 @@ int unpin_extent_cache(struct extent_map_tree *tree, u64 start, u64 len)
        write_lock(&tree->lock);
        em = lookup_extent_mapping(tree, start, len);
 
-       WARN_ON(em->start != start || !em);
+       WARN_ON(!em || em->start != start);
 
        if (!em)
                goto out;