[Cluster-devel] [PATCH dlm/next 4/5] fs: dlm: ls_count busy wait to event based wait

[Alexander Aring <aahringo@redhat.com>]

This patch changes the ls_count busy wait to use atomic counter values
and wait_event() to wait until ls_count reach zero. It will slightly
reduce the number of holding lslist_lock. At remove lockspace we need to
retry the wait because it a lockspace get could interefere between
wait_event() and holding the lock which deletes the lockspace list entry.

Signed-off-by: Alexander Aring <aahringo@redhat.com>
---
 fs/dlm/dlm_internal.h |  3 ++-
 fs/dlm/lockspace.c    | 33 +++++++++++++++++----------------
 fs/dlm/requestqueue.c |  2 +-
 3 files changed, 20 insertions(+), 18 deletions(-)

diff --git a/fs/dlm/dlm_internal.h b/fs/dlm/dlm_internal.h
index fc6505067c80..49cf83e04c80 100644
--- a/fs/dlm/dlm_internal.h
+++ b/fs/dlm/dlm_internal.h
@@ -554,8 +554,9 @@ struct dlm_ls {
 	uint32_t		ls_generation;
 	uint32_t		ls_exflags;
 	int			ls_lvblen;
-	int			ls_count;	/* refcount of processes in
+	atomic_t		ls_count;	/* refcount of processes in
 						   the dlm using this ls */
+	wait_queue_head_t	ls_count_wait;
 	int			ls_create_count; /* create/release refcount */
 	unsigned long		ls_flags;	/* LSFL_ */
 	unsigned long		ls_scan_time;
diff --git a/fs/dlm/lockspace.c b/fs/dlm/lockspace.c
index de1c4af5eb8c..2896f96cf2d3 100644
--- a/fs/dlm/lockspace.c
+++ b/fs/dlm/lockspace.c
@@ -314,7 +314,7 @@ struct dlm_ls *dlm_find_lockspace_global(uint32_t id)
 
 	list_for_each_entry(ls, &lslist, ls_list) {
 		if (ls->ls_global_id == id) {
-			ls->ls_count++;
+			atomic_inc(&ls->ls_count);
 			goto out;
 		}
 	}
@@ -331,7 +331,7 @@ struct dlm_ls *dlm_find_lockspace_local(dlm_lockspace_t *lockspace)
 	spin_lock(&lslist_lock);
 	list_for_each_entry(ls, &lslist, ls_list) {
 		if (ls->ls_local_handle == lockspace) {
-			ls->ls_count++;
+			atomic_inc(&ls->ls_count);
 			goto out;
 		}
 	}
@@ -348,7 +348,7 @@ struct dlm_ls *dlm_find_lockspace_device(int minor)
 	spin_lock(&lslist_lock);
 	list_for_each_entry(ls, &lslist, ls_list) {
 		if (ls->ls_device.minor == minor) {
-			ls->ls_count++;
+			atomic_inc(&ls->ls_count);
 			goto out;
 		}
 	}
@@ -360,24 +360,24 @@ struct dlm_ls *dlm_find_lockspace_device(int minor)
 
 void dlm_put_lockspace(struct dlm_ls *ls)
 {
-	spin_lock(&lslist_lock);
-	ls->ls_count--;
-	spin_unlock(&lslist_lock);
+	if (atomic_dec_and_test(&ls->ls_count))
+		wake_up(&ls->ls_count_wait);
 }
 
 static void remove_lockspace(struct dlm_ls *ls)
 {
-	for (;;) {
-		spin_lock(&lslist_lock);
-		if (ls->ls_count == 0) {
-			WARN_ON(ls->ls_create_count != 0);
-			list_del(&ls->ls_list);
-			spin_unlock(&lslist_lock);
-			return;
-		}
+retry:
+	wait_event(ls->ls_count_wait, atomic_read(&ls->ls_count) == 0);
+
+	spin_lock(&lslist_lock);
+	if (atomic_read(&ls->ls_count) != 0) {
 		spin_unlock(&lslist_lock);
-		ssleep(1);
+		goto retry;
 	}
+
+	WARN_ON(ls->ls_create_count != 0);
+	list_del(&ls->ls_list);
+	spin_unlock(&lslist_lock);
 }
 
 static int threads_start(void)
@@ -481,7 +481,8 @@ static int new_lockspace(const char *name, const char *cluster,
 	memcpy(ls->ls_name, name, namelen);
 	ls->ls_namelen = namelen;
 	ls->ls_lvblen = lvblen;
-	ls->ls_count = 0;
+	atomic_set(&ls->ls_count, 0);
+	init_waitqueue_head(&ls->ls_count_wait);
 	ls->ls_flags = 0;
 	ls->ls_scan_time = jiffies;
 
diff --git a/fs/dlm/requestqueue.c b/fs/dlm/requestqueue.c
index d0cf68570dcf..ccb5307c21e9 100644
--- a/fs/dlm/requestqueue.c
+++ b/fs/dlm/requestqueue.c
@@ -127,7 +127,7 @@ static int purge_request(struct dlm_ls *ls, struct dlm_message *ms, int nodeid)
 	uint32_t type = ms->m_type;
 
 	/* the ls is being cleaned up and freed by release_lockspace */
-	if (!ls->ls_count)
+	if (!atomic_read(&ls->ls_count))
 		return 1;
 
 	if (dlm_is_removed(ls, nodeid))
-- 
2.27.0