f2fs: fix the use of XATTR_NODE_OFFSET

This patch fixes the use of XATTR_NODE_OFFSET.

o The offset should not use several MSB bits which are used by marking node
blocks.

o IS_DNODE should handle XATTR_NODE_OFFSET to avoid potential abnormality
during the fsync call.
Signed-off-by: Jaegeuk Kim <jaegeuk.kim@samsung.com>

fs/f2fs/f2fs.h

@@ -135,11 +135,13 @@ static inline int update_sits_in_cursum(struct f2fs_summary_block *rs, int i)
 /*
  * For INODE and NODE manager
  */
-#define XATTR_NODE_OFFSET	(-1)	/*
-					 * store xattrs to one node block per
-					 * file keeping -1 as its node offset to
-					 * distinguish from index node blocks.
-					 */
+/*
+ * XATTR_NODE_OFFSET stores xattrs to one node block per file keeping -1
+ * as its node offset to distinguish from index node blocks.
+ * But some bits are used to mark the node block.
+ */
+#define XATTR_NODE_OFFSET	((((unsigned int)-1) << OFFSET_BIT_SHIFT) \
+				>> OFFSET_BIT_SHIFT)
 enum {
 	ALLOC_NODE,			/* allocate a new node page if needed */
 	LOOKUP_NODE,			/* look up a node without readahead */

fs/f2fs/node.h

@@ -229,6 +229,10 @@ static inline block_t next_blkaddr_of_node(struct page *node_page)
 static inline bool IS_DNODE(struct page *node_page)
 {
 	unsigned int ofs = ofs_of_node(node_page);
+
+	if (ofs == XATTR_NODE_OFFSET)
+		return false;
+
 	if (ofs == 3 || ofs == 4 + NIDS_PER_BLOCK ||
 			ofs == 5 + 2 * NIDS_PER_BLOCK)
 		return false;