Btrfs: check return value of btrfs_alloc_path()

Adding the check on the return value of btrfs_alloc_path() to several places.
And, some of callers are modified by this change.

Signed-off-by: Tsutomu Itoh <t-itoh@jp.fujitsu.com>
Signed-off-by: Chris Mason <chris.mason@oracle.com>
diff --git a/fs/btrfs/compression.c b/fs/btrfs/compression.c
index 992a4b9..41d1d7c 100644
--- a/fs/btrfs/compression.c
+++ b/fs/btrfs/compression.c
@@ -663,8 +663,9 @@
 			atomic_inc(&cb->pending_bios);
 
 			if (!(BTRFS_I(inode)->flags & BTRFS_INODE_NODATASUM)) {
-				btrfs_lookup_bio_sums(root, inode, comp_bio,
-						      sums);
+				ret = btrfs_lookup_bio_sums(root, inode,
+							comp_bio, sums);
+				BUG_ON(ret);
 			}
 			sums += (comp_bio->bi_size + root->sectorsize - 1) /
 				root->sectorsize;
@@ -689,8 +690,10 @@
 	ret = btrfs_bio_wq_end_io(root->fs_info, comp_bio, 0);
 	BUG_ON(ret);
 
-	if (!(BTRFS_I(inode)->flags & BTRFS_INODE_NODATASUM))
-		btrfs_lookup_bio_sums(root, inode, comp_bio, sums);
+	if (!(BTRFS_I(inode)->flags & BTRFS_INODE_NODATASUM)) {
+		ret = btrfs_lookup_bio_sums(root, inode, comp_bio, sums);
+		BUG_ON(ret);
+	}
 
 	ret = btrfs_map_bio(root, READ, comp_bio, mirror_num, 0);
 	BUG_ON(ret);