xfs: convert log grant heads to atomic variables

Convert the log grant heads to atomic64_t types in preparation for
converting the accounting algorithms to atomic operations. his patch
just converts the variables; the algorithmic changes are in a
separate patch for clarity.
Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>

fs/xfs/xfs_log.c

@@ -47,7 +47,7 @@ STATIC xlog_t *  xlog_alloc_log(xfs_mount_t	*mp,
 				xfs_buftarg_t	*log_target,
 				xfs_daddr_t	blk_offset,
 				int		num_bblks);
-STATIC int	 xlog_space_left(struct log *log, int64_t *head);
+STATIC int	 xlog_space_left(struct log *log, atomic64_t *head);
 STATIC int	 xlog_sync(xlog_t *log, xlog_in_core_t *iclog);
 STATIC void	 xlog_dealloc_log(xlog_t *log);
 
@@ -100,7 +100,7 @@ STATIC int	xlog_iclogs_empty(xlog_t *log);
 static void
 xlog_grant_sub_space(
 	struct log	*log,
-	int64_t		*head,
+	atomic64_t	*head,
 	int		bytes)
 {
 	int		cycle, space;
@@ -119,7 +119,7 @@ xlog_grant_sub_space(
 static void
 xlog_grant_add_space(
 	struct log	*log,
-	int64_t		*head,
+	atomic64_t	*head,
 	int		bytes)
 {
 	int		tmp;
@@ -816,7 +816,7 @@ xlog_assign_tail_lsn(
 STATIC int
 xlog_space_left(
 	struct log	*log,
-	int64_t		*head)
+	atomic64_t	*head)
 {
 	int		free_bytes;
 	int		tail_bytes;

fs/xfs/xfs_log_priv.h

@@ -514,8 +514,8 @@ typedef struct log {
 	spinlock_t		l_grant_lock ____cacheline_aligned_in_smp;
 	struct list_head	l_reserveq;
 	struct list_head	l_writeq;
-	int64_t			l_grant_reserve_head;
-	int64_t			l_grant_write_head;
+	atomic64_t			l_grant_reserve_head;
+	atomic64_t			l_grant_write_head;
 
 	/*
 	 * l_last_sync_lsn and l_tail_lsn are atomics so they can be set and
@@ -596,18 +596,18 @@ xlog_assign_atomic_lsn(atomic64_t *lsn, uint cycle, uint block)
  * will always get consistent component values to work from.
  */
 static inline void
-xlog_crack_grant_head(int64_t *head, int *cycle, int *space)
+xlog_crack_grant_head(atomic64_t *head, int *cycle, int *space)
 {
-	int64_t	val = *head;
+	int64_t	val = atomic64_read(head);
 
 	*cycle = val >> 32;
 	*space = val & 0xffffffff;
 }
 
 static inline void
-xlog_assign_grant_head(int64_t *head, int cycle, int space)
+xlog_assign_grant_head(atomic64_t *head, int cycle, int space)
 {
-	*head = ((int64_t)cycle << 32) | space;
+	atomic64_set(head, ((int64_t)cycle << 32) | space);
 }
 
 /*