Btrfs: fix uncheck memory allocations

To make Btrfs code more robust, several return value checks where memory
allocation can fail are introduced. I use BUG_ON where I don't know how
to handle the error properly, which increases the number of using the
notorious BUG_ON, though.

Signed-off-by: Yoshinori Sano <yoshinori.sano@gmail.com>
Signed-off-by: Chris Mason <chris.mason@oracle.com>

fs/btrfs/extent-tree.c

@@ -6978,6 +6978,10 @@ static noinline int get_new_locations(struct inode *reloc_inode,
 			struct disk_extent *old = exts;
 			max *= 2;
 			exts = kzalloc(sizeof(*exts) * max, GFP_NOFS);
+			if (!exts) {
+				ret = -ENOMEM;
+				goto out;
+			}
 			memcpy(exts, old, sizeof(*exts) * nr);
 			if (old != *extents)
 				kfree(old);