Btrfs: handle only applicable errors returned by btrfs_get_extent

btrfs_get_extent() never returns NULL pointers, so this code introduces
a static checker warning.

The btrfs_get_extent() is a bit complex, but trust me that it doesn't
return NULLs and also if it did we would trigger the BUG_ON(!em) before
the last return statement.
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
[ updated subject ]
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/file.c

@@ -2342,13 +2342,8 @@ static int find_first_non_hole(struct inode *inode, u64 *start, u64 *len)
 	int ret = 0;
 
 	em = btrfs_get_extent(BTRFS_I(inode), NULL, 0, *start, *len, 0);
-	if (IS_ERR_OR_NULL(em)) {
-		if (!em)
-			ret = -ENOMEM;
-		else
-			ret = PTR_ERR(em);
-		return ret;
-	}
+	if (IS_ERR(em))
+		return PTR_ERR(em);
 
 	/* Hole or vacuum extent(only exists in no-hole mode) */
 	if (em->block_start == EXTENT_MAP_HOLE) {
@@ -2835,10 +2830,7 @@ static long btrfs_fallocate(struct file *file, int mode,
 	while (1) {
 		em = btrfs_get_extent(BTRFS_I(inode), NULL, 0, cur_offset,
 				      alloc_end - cur_offset, 0);
-		if (IS_ERR_OR_NULL(em)) {
-			if (!em)
-				ret = -ENOMEM;
-			else
+		if (IS_ERR(em)) {
 			ret = PTR_ERR(em);
 			break;
 		}

fs/btrfs/inode.c

@@ -6736,7 +6736,6 @@ static noinline int uncompress_inline(struct btrfs_path *path,
  *
  * This also copies inline extents directly into the page.
  */
-
 struct extent_map *btrfs_get_extent(struct btrfs_inode *inode,
 		struct page *page,
 	    size_t pg_offset, u64 start, u64 len,
@@ -7045,9 +7044,8 @@ struct extent_map *btrfs_get_extent_fiemap(struct btrfs_inode *inode,
 	em = btrfs_get_extent(inode, page, pg_offset, start, len, create);
 	if (IS_ERR(em))
 		return em;
-	if (em) {
 	/*
-		 * if our em maps to
+	 * If our em maps to:
 	 * - a hole or
 	 * - a pre-alloc extent,
 	 * there might actually be delalloc bytes behind it.
@@ -7057,7 +7055,6 @@ struct extent_map *btrfs_get_extent_fiemap(struct btrfs_inode *inode,
 		return em;
 	else
 		hole_em = em;
-	}
 
 	/* check to see if we've wrapped (len == -1 or similar) */
 	end = start + len;