[PATCH 2/4] xfs: remove callback dequeue loop from xlog_state_do_iclog_callbacks

[Dave Chinner <david@fromorbit.com>]

From: Dave Chinner <dchinner@redhat.com>

If we are processing callbacks on an iclog, nothing can be
concurrently adding callbacks to the loop. We only add callbacks to
the iclog when they are in ACTIVE or WANT_SYNC state, and we
explicitly do not add callbacks if the iclog is already in IOERROR
state.

The only way to have a dequeue racing with an enqueue is to be
processing a shutdown without a direct reference to an iclog in
ACTIVE or WANT_SYNC state. As the enqueue avoids this race
condition, we only ever need a single dequeue operation in
xlog_state_do_iclog_callbacks(). Hence we can remove the loop.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
---
 fs/xfs/xfs_log.c | 16 ++++++----------
 1 file changed, 6 insertions(+), 10 deletions(-)

diff --git a/fs/xfs/xfs_log.c b/fs/xfs/xfs_log.c
index bb4390942275..05b00fa4d661 100644
--- a/fs/xfs/xfs_log.c
+++ b/fs/xfs/xfs_log.c
@@ -2774,19 +2774,15 @@ xlog_state_do_iclog_callbacks(
 	struct xlog		*log,
 	struct xlog_in_core	*iclog)
 {
-	trace_xlog_iclog_callbacks_start(iclog, _RET_IP_);
-	spin_lock(&iclog->ic_callback_lock);
-	while (!list_empty(&iclog->ic_callbacks)) {
-		LIST_HEAD(tmp);
+	LIST_HEAD(tmp);
 
-		list_splice_init(&iclog->ic_callbacks, &tmp);
-
-		spin_unlock(&iclog->ic_callback_lock);
-		xlog_cil_process_committed(&tmp);
-		spin_lock(&iclog->ic_callback_lock);
-	}
+	trace_xlog_iclog_callbacks_start(iclog, _RET_IP_);
 
+	spin_lock(&iclog->ic_callback_lock);
+	list_splice_init(&iclog->ic_callbacks, &tmp);
 	spin_unlock(&iclog->ic_callback_lock);
+
+	xlog_cil_process_committed(&tmp);
 	trace_xlog_iclog_callbacks_done(iclog, _RET_IP_);
 }
 
-- 
2.31.1