fs: dlm: requestqueue busy wait to event based wait

This patch changes the requestqueue busy waiting algorithm to use
atomic counter values and wait_event() to wait until the requestqueue is
empty. It will slightly reduce the number of holding ls_requestqueue_mutex
mutex.

Signed-off-by: Alexander Aring <aahringo@redhat.com>
Signed-off-by: David Teigland <teigland@redhat.com>

fs/dlm/dlm_internal.h

@@ -626,6 +626,8 @@ struct dlm_ls {
 	struct rw_semaphore	ls_in_recovery;	/* block local requests */
 	struct rw_semaphore	ls_recv_active;	/* block dlm_recv */
 	struct list_head	ls_requestqueue;/* queue remote requests */
+	atomic_t		ls_requestqueue_cnt;
+	wait_queue_head_t	ls_requestqueue_wait;
 	struct mutex		ls_requestqueue_mutex;
 	struct dlm_rcom		*ls_recover_buf;
 	int			ls_recover_nodeid; /* for debugging */

fs/dlm/lockspace.c

@@ -564,6 +564,8 @@ static int new_lockspace(const char *name, const char *cluster,
 	init_rwsem(&ls->ls_in_recovery);
 	init_rwsem(&ls->ls_recv_active);
 	INIT_LIST_HEAD(&ls->ls_requestqueue);
+	atomic_set(&ls->ls_requestqueue_cnt, 0);
+	init_waitqueue_head(&ls->ls_requestqueue_wait);
 	mutex_init(&ls->ls_requestqueue_mutex);
 	mutex_init(&ls->ls_clear_proc_locks);
 

fs/dlm/requestqueue.c

@@ -44,6 +44,7 @@ void dlm_add_requestqueue(struct dlm_ls *ls, int nodeid, struct dlm_message *ms)
 	e->nodeid = nodeid;
 	memcpy(&e->request, ms, ms->m_header.h_length);
 
+	atomic_inc(&ls->ls_requestqueue_cnt);
 	mutex_lock(&ls->ls_requestqueue_mutex);
 	list_add_tail(&e->list, &ls->ls_requestqueue);
 	mutex_unlock(&ls->ls_requestqueue_mutex);
@@ -89,6 +90,8 @@ int dlm_process_requestqueue(struct dlm_ls *ls)
 
 		mutex_lock(&ls->ls_requestqueue_mutex);
 		list_del(&e->list);
+		if (atomic_dec_and_test(&ls->ls_requestqueue_cnt))
+			wake_up(&ls->ls_requestqueue_wait);
 		kfree(e);
 
 		if (dlm_locking_stopped(ls)) {
@@ -115,14 +118,8 @@ int dlm_process_requestqueue(struct dlm_ls *ls)
 
 void dlm_wait_requestqueue(struct dlm_ls *ls)
 {
-	for (;;) {
-		mutex_lock(&ls->ls_requestqueue_mutex);
-		if (list_empty(&ls->ls_requestqueue))
-			break;
-		mutex_unlock(&ls->ls_requestqueue_mutex);
-		schedule();
-	}
-	mutex_unlock(&ls->ls_requestqueue_mutex);
+	wait_event(ls->ls_requestqueue_wait,
+		   atomic_read(&ls->ls_requestqueue_cnt) == 0);
 }
 
 static int purge_request(struct dlm_ls *ls, struct dlm_message *ms, int nodeid)
@@ -161,6 +158,8 @@ void dlm_purge_requestqueue(struct dlm_ls *ls)
 
 		if (purge_request(ls, ms, e->nodeid)) {
 			list_del(&e->list);
+			if (atomic_dec_and_test(&ls->ls_requestqueue_cnt))
+				wake_up(&ls->ls_requestqueue_wait);
 			kfree(e);
 		}
 	}