xfs: don't nest icloglock inside ic_callback_lock

It's completely unnecessary because callbacks are added to iclogs
without holding the icloglock, hence no amount of ordering between
the icloglock and ic_callback_lock will order the removal of
callbacks from the iclog.
Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Brian Foster <bfoster@redhat.com>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Darrick J. Wong <djwong@kernel.org>

fs/xfs/xfs_log.c

@@ -2773,11 +2773,8 @@ static void
 xlog_state_do_iclog_callbacks(
 	struct xlog		*log,
 	struct xlog_in_core	*iclog)
-		__releases(&log->l_icloglock)
-		__acquires(&log->l_icloglock)
 {
 	trace_xlog_iclog_callbacks_start(iclog, _RET_IP_);
-	spin_unlock(&log->l_icloglock);
 	spin_lock(&iclog->ic_callback_lock);
 	while (!list_empty(&iclog->ic_callbacks)) {
 		LIST_HEAD(tmp);
@@ -2789,12 +2786,6 @@ xlog_state_do_iclog_callbacks(
 		spin_lock(&iclog->ic_callback_lock);
 	}
 
-	/*
-	 * Pick up the icloglock while still holding the callback lock so we
-	 * serialise against anyone trying to add more callbacks to this iclog
-	 * now we've finished processing.
-	 */
-	spin_lock(&log->l_icloglock);
 	spin_unlock(&iclog->ic_callback_lock);
 	trace_xlog_iclog_callbacks_done(iclog, _RET_IP_);
 }
@@ -2836,13 +2827,12 @@ xlog_state_do_callback(
 				iclog = iclog->ic_next;
 				continue;
 			}
+			spin_unlock(&log->l_icloglock);
 
-			/*
-			 * Running callbacks will drop the icloglock which means
-			 * we'll have to run at least one more complete loop.
-			 */
-			cycled_icloglock = true;
 			xlog_state_do_iclog_callbacks(log, iclog);
+			cycled_icloglock = true;
+
+			spin_lock(&log->l_icloglock);
 			if (XLOG_FORCED_SHUTDOWN(log))
 				wake_up_all(&iclog->ic_force_wait);
 			else