fsnotify: convert notification_mutex to a spinlock

notification_mutex is used to protect the list of pending events.  As such
there's no reason to use a sleeping lock for it.  Convert it to a
spinlock.

[jack@suse.cz: fixed version]
  Link: http://lkml.kernel.org/r/1474031567-1831-1-git-send-email-jack@suse.cz
Link: http://lkml.kernel.org/r/1473797711-14111-5-git-send-email-jack@suse.cz
Signed-off-by: Jan Kara <jack@suse.cz>
Reviewed-by: Lino Sanfilippo <LinoSanfilippo@gmx.de>
Tested-by: Guenter Roeck <linux@roeck-us.net>
Cc: Miklos Szeredi <mszeredi@redhat.com>
Cc: Eric Paris <eparis@redhat.com>
Cc: Al Viro <viro@ZenIV.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 15 insertions, 12 deletions

diff --git a/fs/notify/notification.c b/fs/notify/notification.c
index 7d563dea52a4..8a7a8cd041e8 100644
--- a/fs/notify/notification.c
+++ b/fs/notify/notification.c
@@ -63,7 +63,8 @@ EXPORT_SYMBOL_GPL(fsnotify_get_cookie);
 /* return true if the notify queue is empty, false otherwise */
 bool fsnotify_notify_queue_is_empty(struct fsnotify_group *group)
 {
-	BUG_ON(!mutex_is_locked(&group->notification_mutex));
+	BUG_ON(IS_ENABLED(CONFIG_SMP) &&
+	       !spin_is_locked(&group->notification_lock));
 	return list_empty(&group->notification_list) ? true : false;
 }
 
@@ -95,10 +96,10 @@ int fsnotify_add_event(struct fsnotify_group *group,
 
 	pr_debug("%s: group=%p event=%p\n", __func__, group, event);
 
-	mutex_lock(&group->notification_mutex);
+	spin_lock(&group->notification_lock);
 
 	if (group->shutdown) {
-		mutex_unlock(&group->notification_mutex);
+		spin_unlock(&group->notification_lock);
 		return 2;
 	}
 
@@ -106,7 +107,7 @@ int fsnotify_add_event(struct fsnotify_group *group,
 		ret = 2;
 		/* Queue overflow event only if it isn't already queued */
 		if (!list_empty(&group->overflow_event->list)) {
-			mutex_unlock(&group->notification_mutex);
+			spin_unlock(&group->notification_lock);
 			return ret;
 		}
 		event = group->overflow_event;
@@ -116,7 +117,7 @@ int fsnotify_add_event(struct fsnotify_group *group,
 	if (!list_empty(list) && merge) {
 		ret = merge(list, event);
 		if (ret) {
-			mutex_unlock(&group->notification_mutex);
+			spin_unlock(&group->notification_lock);
 			return ret;
 		}
 	}
@@ -124,7 +125,7 @@ int fsnotify_add_event(struct fsnotify_group *group,
 queue:
 	group->q_len++;
 	list_add_tail(&event->list, list);
-	mutex_unlock(&group->notification_mutex);
+	spin_unlock(&group->notification_lock);
 
 	wake_up(&group->notification_waitq);
 	kill_fasync(&group->fsn_fa, SIGIO, POLL_IN);
@@ -139,7 +140,8 @@ struct fsnotify_event *fsnotify_remove_first_event(struct fsnotify_group *group)
 {
 	struct fsnotify_event *event;
 
-	BUG_ON(!mutex_is_locked(&group->notification_mutex));
+	BUG_ON(IS_ENABLED(CONFIG_SMP) &&
+	       !spin_is_locked(&group->notification_lock));
 
 	pr_debug("%s: group=%p\n", __func__, group);
 
@@ -161,7 +163,8 @@ struct fsnotify_event *fsnotify_remove_first_event(struct fsnotify_group *group)
  */
 struct fsnotify_event *fsnotify_peek_first_event(struct fsnotify_group *group)
 {
-	BUG_ON(!mutex_is_locked(&group->notification_mutex));
+	BUG_ON(IS_ENABLED(CONFIG_SMP) &&
+	       !spin_is_locked(&group->notification_lock));
 
 	return list_first_entry(&group->notification_list,
 				struct fsnotify_event, list);
@@ -175,14 +178,14 @@ void fsnotify_flush_notify(struct fsnotify_group *group)
 {
 	struct fsnotify_event *event;
 
-	mutex_lock(&group->notification_mutex);
+	spin_lock(&group->notification_lock);
 	while (!fsnotify_notify_queue_is_empty(group)) {
 		event = fsnotify_remove_first_event(group);
-		mutex_unlock(&group->notification_mutex);
+		spin_unlock(&group->notification_lock);
 		fsnotify_destroy_event(group, event);
-		mutex_lock(&group->notification_mutex);
+		spin_lock(&group->notification_lock);
 	}
-	mutex_unlock(&group->notification_mutex);
+	spin_unlock(&group->notification_lock);
 }
 
 /*