xfs: fold sbcount quiesce logging into log covering

xfs_log_sbcount() calls xfs_sync_sb() to sync superblock counters to
disk when lazy superblock accounting is enabled. This occurs on
unmount, freeze, and read-only (re)mount and ensures the final
values are calculated and persisted to disk before each form of
quiesce completes.

Now that log covering occurs in all of these contexts and uses the
same xfs_sync_sb() mechanism to update log state, there is no need
to log the superblock separately for any reason. Update the log
quiesce path to sync the superblock at least once for any mount
where lazy superblock accounting is enabled. If the log is already
covered, it will remain in the covered state. Otherwise, the next
sync as part of the normal covering sequence will carry the
associated superblock update with it. Remove xfs_log_sbcount() now
that it is no longer needed.
Signed-off-by: NBrian Foster <bfoster@redhat.com>
Reviewed-by: NDarrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: NDarrick J. Wong <djwong@kernel.org>
Signed-off-by: NDarrick J. Wong <djwong@kernel.org>
Reviewed-by: NAllison Henderson <allison.henderson@oracle.com>

fs/xfs/xfs_log.c

@@ -1110,6 +1110,7 @@ xfs_log_cover(
 {
 	struct xlog		*log = mp->m_log;
 	int			error = 0;
+	bool			need_covered;
 
 	ASSERT((xlog_cil_empty(log) && xlog_iclogs_empty(log) &&
 	        !xfs_ail_min_lsn(log->l_ailp)) ||
@@ -1118,6 +1119,21 @@ xfs_log_cover(
 	if (!xfs_log_writable(mp))
 		return 0;
 
+	/*
+	 * xfs_log_need_covered() is not idempotent because it progresses the
+	 * state machine if the log requires covering. Therefore, we must call
+	 * this function once and use the result until we've issued an sb sync.
+	 * Do so first to make that abundantly clear.
+	 *
+	 * Fall into the covering sequence if the log needs covering or the
+	 * mount has lazy superblock accounting to sync to disk. The sb sync
+	 * used for covering accumulates the in-core counters, so covering
+	 * handles this for us.
+	 */
+	need_covered = xfs_log_need_covered(mp);
+	if (!need_covered && !xfs_sb_version_haslazysbcount(&mp->m_sb))
+		return 0;
+
 	/*
 	 * To cover the log, commit the superblock twice (at most) in
 	 * independent checkpoints. The first serves as a reference for the
@@ -1127,12 +1143,12 @@ xfs_log_cover(
 	 * covering the log. Push the AIL one more time to leave it empty, as
 	 * we found it.
 	 */
-	while (xfs_log_need_covered(mp)) {
+	do {
 		error = xfs_sync_sb(mp, true);
 		if (error)
 			break;
 		xfs_ail_push_all_sync(mp->m_ail);
-	}
+	} while (xfs_log_need_covered(mp));
 
 	return error;
 }

fs/xfs/xfs_mount.c

@@ -1124,12 +1124,6 @@ xfs_unmountfs(
 		xfs_warn(mp, "Unable to free reserved block pool. "
 				"Freespace may not be correct on next mount.");
 
-	error = xfs_log_sbcount(mp);
-	if (error)
-		xfs_warn(mp, "Unable to update superblock counters. "
-				"Freespace may not be correct on next mount.");
-
-
 	xfs_log_unmount(mp);
 	xfs_da_unmount(mp);
 	xfs_uuid_unmount(mp);
@@ -1164,31 +1158,6 @@ xfs_fs_writable(
 	return true;
 }
 
-/*
- * xfs_log_sbcount
- *
- * Sync the superblock counters to disk.
- *
- * Note this code can be called during the process of freezing, so we use the
- * transaction allocator that does not block when the transaction subsystem is
- * in its frozen state.
- */
-int
-xfs_log_sbcount(xfs_mount_t *mp)
-{
-	if (!xfs_log_writable(mp))
-		return 0;
-
-	/*
-	 * we don't need to do this if we are updating the superblock
-	 * counters on every modification.
-	 */
-	if (!xfs_sb_version_haslazysbcount(&mp->m_sb))
-		return 0;
-
-	return xfs_sync_sb(mp, true);
-}
-
 /*
  * Deltas for the block count can vary from 1 to very large, but lock contention
  * only occurs on frequent small block count updates such as in the delayed

fs/xfs/xfs_mount.h

@@ -399,7 +399,6 @@ int xfs_buf_hash_init(xfs_perag_t *pag);
 void xfs_buf_hash_destroy(xfs_perag_t *pag);
 
 extern void	xfs_uuid_table_free(void);
-extern int	xfs_log_sbcount(xfs_mount_t *);
 extern uint64_t xfs_default_resblks(xfs_mount_t *mp);
 extern int	xfs_mountfs(xfs_mount_t *mp);
 extern int	xfs_initialize_perag(xfs_mount_t *mp, xfs_agnumber_t agcount,

fs/xfs/xfs_super.c

@@ -884,19 +884,11 @@ void
 xfs_quiesce_attr(
 	struct xfs_mount	*mp)
 {
-	int	error = 0;
-
 	cancel_delayed_work_sync(&mp->m_log->l_work);
 
 	/* force the log to unpin objects from the now complete transactions */
 	xfs_log_force(mp, XFS_LOG_SYNC);
 
-
-	/* Push the superblock and write an unmount record */
-	error = xfs_log_sbcount(mp);
-	if (error)
-		xfs_warn(mp, "xfs_attr_quiesce: failed to log sb changes. "
-				"Frozen image may not be consistent.");
 	xfs_log_clean(mp);
 }