1 files changed, 83 insertions, 56 deletions

diff --git a/fs/xfs/xfs_log.c b/fs/xfs/xfs_log.c
index a1d7d12..6fcc9d0 100644
--- a/fs/xfs/xfs_log.c
+++ b/fs/xfs/xfs_log.c
@@ -682,12 +682,12 @@ xfs_log_move_tail(xfs_mount_t	*mp,
 	if (tail_lsn != 1)
 		atomic64_set(&log->l_tail_lsn, tail_lsn);
 
-	spin_lock(&log->l_grant_lock);
-	if (!list_empty(&log->l_writeq)) {
+	if (!list_empty_careful(&log->l_writeq)) {
 #ifdef DEBUG
 		if (log->l_flags & XLOG_ACTIVE_RECOVERY)
 			panic("Recovery problem");
 #endif
+		spin_lock(&log->l_grant_write_lock);
 		free_bytes = xlog_space_left(log, &log->l_grant_write_head);
 		list_for_each_entry(tic, &log->l_writeq, t_queue) {
 			ASSERT(tic->t_flags & XLOG_TIC_PERM_RESERV);
@@ -696,15 +696,18 @@ xfs_log_move_tail(xfs_mount_t	*mp,
 				break;
 			tail_lsn = 0;
 			free_bytes -= tic->t_unit_res;
+			trace_xfs_log_regrant_write_wake_up(log, tic);
 			wake_up(&tic->t_wait);
 		}
+		spin_unlock(&log->l_grant_write_lock);
 	}
 
-	if (!list_empty(&log->l_reserveq)) {
+	if (!list_empty_careful(&log->l_reserveq)) {
 #ifdef DEBUG
 		if (log->l_flags & XLOG_ACTIVE_RECOVERY)
 			panic("Recovery problem");
 #endif
+		spin_lock(&log->l_grant_reserve_lock);
 		free_bytes = xlog_space_left(log, &log->l_grant_reserve_head);
 		list_for_each_entry(tic, &log->l_reserveq, t_queue) {
 			if (tic->t_flags & XLOG_TIC_PERM_RESERV)
@@ -715,11 +718,12 @@ xfs_log_move_tail(xfs_mount_t	*mp,
 				break;
 			tail_lsn = 0;
 			free_bytes -= need_bytes;
+			trace_xfs_log_grant_wake_up(log, tic);
 			wake_up(&tic->t_wait);
 		}
+		spin_unlock(&log->l_grant_reserve_lock);
 	}
-	spin_unlock(&log->l_grant_lock);
-}	/* xfs_log_move_tail */
+}
 
 /*
  * Determine if we have a transaction that has gone to disk
@@ -1010,6 +1014,8 @@ xlog_alloc_log(xfs_mount_t	*mp,
 	xlog_assign_grant_head(&log->l_grant_write_head, 1, 0);
 	INIT_LIST_HEAD(&log->l_reserveq);
 	INIT_LIST_HEAD(&log->l_writeq);
+	spin_lock_init(&log->l_grant_reserve_lock);
+	spin_lock_init(&log->l_grant_write_lock);
 
 	error = EFSCORRUPTED;
 	if (xfs_sb_version_hassector(&mp->m_sb)) {
@@ -2477,6 +2483,18 @@ restart:
  *
  * Once a ticket gets put onto the reserveq, it will only return after
  * the needed reservation is satisfied.
+ *
+ * This function is structured so that it has a lock free fast path. This is
+ * necessary because every new transaction reservation will come through this
+ * path. Hence any lock will be globally hot if we take it unconditionally on
+ * every pass.
+ *
+ * As tickets are only ever moved on and off the reserveq under the
+ * l_grant_reserve_lock, we only need to take that lock if we are going
+ * to add the ticket to the queue and sleep. We can avoid taking the lock if the
+ * ticket was never added to the reserveq because the t_queue list head will be
+ * empty and we hold the only reference to it so it can safely be checked
+ * unlocked.
  */
 STATIC int
 xlog_grant_log_space(xlog_t	   *log,
@@ -2490,13 +2508,20 @@ xlog_grant_log_space(xlog_t	   *log,
 		panic("grant Recovery problem");
 #endif
 
-	/* Is there space or do we need to sleep? */
-	spin_lock(&log->l_grant_lock);
-
 	trace_xfs_log_grant_enter(log, tic);
 
+	need_bytes = tic->t_unit_res;
+	if (tic->t_flags & XFS_LOG_PERM_RESERV)
+		need_bytes *= tic->t_ocnt;
+
 	/* something is already sleeping; insert new transaction at end */
-	if (!list_empty(&log->l_reserveq)) {
+	if (!list_empty_careful(&log->l_reserveq)) {
+		spin_lock(&log->l_grant_reserve_lock);
+		/* recheck the queue now we are locked */
+		if (list_empty(&log->l_reserveq)) {
+			spin_unlock(&log->l_grant_reserve_lock);
+			goto redo;
+		}
 		list_add_tail(&tic->t_queue, &log->l_reserveq);
 
 		trace_xfs_log_grant_sleep1(log, tic);
@@ -2509,48 +2534,47 @@ xlog_grant_log_space(xlog_t	   *log,
 			goto error_return;
 
 		XFS_STATS_INC(xs_sleep_logspace);
-		xlog_wait(&tic->t_wait, &log->l_grant_lock);
+		xlog_wait(&tic->t_wait, &log->l_grant_reserve_lock);
 
 		/*
 		 * If we got an error, and the filesystem is shutting down,
 		 * we'll catch it down below. So just continue...
 		 */
 		trace_xfs_log_grant_wake1(log, tic);
-		spin_lock(&log->l_grant_lock);
 	}
-	if (tic->t_flags & XFS_LOG_PERM_RESERV)
-		need_bytes = tic->t_unit_res*tic->t_ocnt;
-	else
-		need_bytes = tic->t_unit_res;
 
 redo:
 	if (XLOG_FORCED_SHUTDOWN(log))
-		goto error_return;
+		goto error_return_unlocked;
 
 	free_bytes = xlog_space_left(log, &log->l_grant_reserve_head);
 	if (free_bytes < need_bytes) {
+		spin_lock(&log->l_grant_reserve_lock);
 		if (list_empty(&tic->t_queue))
 			list_add_tail(&tic->t_queue, &log->l_reserveq);
 
 		trace_xfs_log_grant_sleep2(log, tic);
 
+		if (XLOG_FORCED_SHUTDOWN(log))
+			goto error_return;
+
 		xlog_grant_push_ail(log, need_bytes);
 
 		XFS_STATS_INC(xs_sleep_logspace);
-		xlog_wait(&tic->t_wait, &log->l_grant_lock);
-
-		spin_lock(&log->l_grant_lock);
-		if (XLOG_FORCED_SHUTDOWN(log))
-			goto error_return;
+		xlog_wait(&tic->t_wait, &log->l_grant_reserve_lock);
 
 		trace_xfs_log_grant_wake2(log, tic);
-
 		goto redo;
 	}
 
-	list_del_init(&tic->t_queue);
+	if (!list_empty(&tic->t_queue)) {
+		spin_lock(&log->l_grant_reserve_lock);
+		list_del_init(&tic->t_queue);
+		spin_unlock(&log->l_grant_reserve_lock);
+	}
 
 	/* we've got enough space */
+	spin_lock(&log->l_grant_lock);
 	xlog_grant_add_space(log, &log->l_grant_reserve_head, need_bytes);
 	xlog_grant_add_space(log, &log->l_grant_write_head, need_bytes);
 	trace_xfs_log_grant_exit(log, tic);
@@ -2559,8 +2583,11 @@ redo:
 	spin_unlock(&log->l_grant_lock);
 	return 0;
 
- error_return:
+error_return_unlocked:
+	spin_lock(&log->l_grant_reserve_lock);
+error_return:
 	list_del_init(&tic->t_queue);
+	spin_unlock(&log->l_grant_reserve_lock);
 	trace_xfs_log_grant_error(log, tic);
 
 	/*
@@ -2570,7 +2597,6 @@ redo:
 	 */
 	tic->t_curr_res = 0;
 	tic->t_cnt = 0; /* ungrant will give back unit_res * t_cnt. */
-	spin_unlock(&log->l_grant_lock);
 	return XFS_ERROR(EIO);
 }	/* xlog_grant_log_space */
 
@@ -2578,7 +2604,8 @@ redo:
 /*
  * Replenish the byte reservation required by moving the grant write head.
  *
- *
+ * Similar to xlog_grant_log_space, the function is structured to have a lock
+ * free fast path.
  */
 STATIC int
 xlog_regrant_write_log_space(xlog_t	   *log,
@@ -2597,12 +2624,9 @@ xlog_regrant_write_log_space(xlog_t	   *log,
 		panic("regrant Recovery problem");
 #endif
 
-	spin_lock(&log->l_grant_lock);
-
 	trace_xfs_log_regrant_write_enter(log, tic);
-
 	if (XLOG_FORCED_SHUTDOWN(log))
-		goto error_return;
+		goto error_return_unlocked;
 
 	/* If there are other waiters on the queue then give them a
 	 * chance at logspace before us. Wake up the first waiters,
@@ -2611,8 +2635,10 @@ xlog_regrant_write_log_space(xlog_t	   *log,
 	 * this transaction.
 	 */
 	need_bytes = tic->t_unit_res;
-	if (!list_empty(&log->l_writeq)) {
+	if (!list_empty_careful(&log->l_writeq)) {
 		struct xlog_ticket *ntic;
+
+		spin_lock(&log->l_grant_write_lock);
 		free_bytes = xlog_space_left(log, &log->l_grant_write_head);
 		list_for_each_entry(ntic, &log->l_writeq, t_queue) {
 			ASSERT(ntic->t_flags & XLOG_TIC_PERM_RESERV);
@@ -2627,50 +2653,48 @@ xlog_regrant_write_log_space(xlog_t	   *log,
 						struct xlog_ticket, t_queue)) {
 			if (list_empty(&tic->t_queue))
 				list_add_tail(&tic->t_queue, &log->l_writeq);
-
 			trace_xfs_log_regrant_write_sleep1(log, tic);
 
 			xlog_grant_push_ail(log, need_bytes);
 
 			XFS_STATS_INC(xs_sleep_logspace);
-			xlog_wait(&tic->t_wait, &log->l_grant_lock);
-
-			/* If we're shutting down, this tic is already
-			 * off the queue */
-			spin_lock(&log->l_grant_lock);
-			if (XLOG_FORCED_SHUTDOWN(log))
-				goto error_return;
-
+			xlog_wait(&tic->t_wait, &log->l_grant_write_lock);
 			trace_xfs_log_regrant_write_wake1(log, tic);
-		}
+		} else
+			spin_unlock(&log->l_grant_write_lock);
 	}
 
 redo:
 	if (XLOG_FORCED_SHUTDOWN(log))
-		goto error_return;
+		goto error_return_unlocked;
 
 	free_bytes = xlog_space_left(log, &log->l_grant_write_head);
 	if (free_bytes < need_bytes) {
+		spin_lock(&log->l_grant_write_lock);
 		if (list_empty(&tic->t_queue))
 			list_add_tail(&tic->t_queue, &log->l_writeq);
+
+		if (XLOG_FORCED_SHUTDOWN(log))
+			goto error_return;
+
 		xlog_grant_push_ail(log, need_bytes);
 
 		XFS_STATS_INC(xs_sleep_logspace);
 		trace_xfs_log_regrant_write_sleep2(log, tic);
-		xlog_wait(&tic->t_wait, &log->l_grant_lock);
-
-		/* If we're shutting down, this tic is already off the queue */
-		spin_lock(&log->l_grant_lock);
-		if (XLOG_FORCED_SHUTDOWN(log))
-			goto error_return;
+		xlog_wait(&tic->t_wait, &log->l_grant_write_lock);
 
 		trace_xfs_log_regrant_write_wake2(log, tic);
 		goto redo;
 	}
 
-	list_del_init(&tic->t_queue);
+	if (!list_empty(&tic->t_queue)) {
+		spin_lock(&log->l_grant_write_lock);
+		list_del_init(&tic->t_queue);
+		spin_unlock(&log->l_grant_write_lock);
+	}
 
 	/* we've got enough space */
+	spin_lock(&log->l_grant_lock);
 	xlog_grant_add_space(log, &log->l_grant_write_head, need_bytes);
 	trace_xfs_log_regrant_write_exit(log, tic);
 	xlog_verify_grant_head(log, 1);
@@ -2679,8 +2703,11 @@ redo:
 	return 0;
 
 
+ error_return_unlocked:
+	spin_lock(&log->l_grant_write_lock);
  error_return:
 	list_del_init(&tic->t_queue);
+	spin_unlock(&log->l_grant_write_lock);
 	trace_xfs_log_regrant_write_error(log, tic);
 
 	/*
@@ -2690,7 +2717,6 @@ redo:
 	 */
 	tic->t_curr_res = 0;
 	tic->t_cnt = 0; /* ungrant will give back unit_res * t_cnt. */
-	spin_unlock(&log->l_grant_lock);
 	return XFS_ERROR(EIO);
 }	/* xlog_regrant_write_log_space */
 
@@ -3664,12 +3690,10 @@ xfs_log_force_umount(
 		xlog_cil_force(log);
 
 	/*
-	 * We must hold both the GRANT lock and the LOG lock,
-	 * before we mark the filesystem SHUTDOWN and wake
-	 * everybody up to tell the bad news.
+	 * mark the filesystem and the as in a shutdown state and wake
+	 * everybody up to tell them the bad news.
 	 */
 	spin_lock(&log->l_icloglock);
-	spin_lock(&log->l_grant_lock);
 	mp->m_flags |= XFS_MOUNT_FS_SHUTDOWN;
 	if (mp->m_sb_bp)
 		XFS_BUF_DONE(mp->m_sb_bp);
@@ -3694,14 +3718,17 @@ xfs_log_force_umount(
 	 * means we have to wake up everybody queued up on reserveq as well as
 	 * writeq.  In addition, we make sure in xlog_{re}grant_log_space that
 	 * we don't enqueue anything once the SHUTDOWN flag is set, and this
-	 * action is protected by the GRANTLOCK.
+	 * action is protected by the grant locks.
 	 */
+	spin_lock(&log->l_grant_reserve_lock);
 	list_for_each_entry(tic, &log->l_reserveq, t_queue)
 		wake_up(&tic->t_wait);
+	spin_unlock(&log->l_grant_reserve_lock);
 
+	spin_lock(&log->l_grant_write_lock);
 	list_for_each_entry(tic, &log->l_writeq, t_queue)
 		wake_up(&tic->t_wait);
-	spin_unlock(&log->l_grant_lock);
+	spin_unlock(&log->l_grant_write_lock);
 
 	if (!(log->l_iclog->ic_state & XLOG_STATE_IOERROR)) {
 		ASSERT(!logerror);