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, 14 insertions, 13 deletions

diff --git a/fs/notify/fanotify/fanotify_user.c b/fs/notify/fanotify/fanotify_user.c
index 46d135c4988f..80091a5dc8c0 100644
--- a/fs/notify/fanotify/fanotify_user.c
+++ b/fs/notify/fanotify/fanotify_user.c
@@ -49,12 +49,13 @@ struct kmem_cache *fanotify_perm_event_cachep __read_mostly;
  * enough to fit in "count". Return an error pointer if the count
  * is not large enough.
  *
- * Called with the group->notification_mutex held.
+ * Called with the group->notification_lock held.
  */
 static struct fsnotify_event *get_one_event(struct fsnotify_group *group,
 					    size_t count)
 {
-	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 count=%zd\n", __func__, group, count);
 
@@ -64,7 +65,7 @@ static struct fsnotify_event *get_one_event(struct fsnotify_group *group,
 	if (FAN_EVENT_METADATA_LEN > count)
 		return ERR_PTR(-EINVAL);
 
-	/* held the notification_mutex the whole time, so this is the
+	/* held the notification_lock the whole time, so this is the
 	 * same event we peeked above */
 	return fsnotify_remove_first_event(group);
 }
@@ -244,10 +245,10 @@ static unsigned int fanotify_poll(struct file *file, poll_table *wait)
 	int ret = 0;
 
 	poll_wait(file, &group->notification_waitq, wait);
-	mutex_lock(&group->notification_mutex);
+	spin_lock(&group->notification_lock);
 	if (!fsnotify_notify_queue_is_empty(group))
 		ret = POLLIN | POLLRDNORM;
-	mutex_unlock(&group->notification_mutex);
+	spin_unlock(&group->notification_lock);
 
 	return ret;
 }
@@ -268,9 +269,9 @@ static ssize_t fanotify_read(struct file *file, char __user *buf,
 
 	add_wait_queue(&group->notification_waitq, &wait);
 	while (1) {
-		mutex_lock(&group->notification_mutex);
+		spin_lock(&group->notification_lock);
 		kevent = get_one_event(group, count);
-		mutex_unlock(&group->notification_mutex);
+		spin_unlock(&group->notification_lock);
 
 		if (IS_ERR(kevent)) {
 			ret = PTR_ERR(kevent);
@@ -387,17 +388,17 @@ static int fanotify_release(struct inode *ignored, struct file *file)
 	 * dequeue them and set the response. They will be freed once the
 	 * response is consumed and fanotify_get_response() returns.
 	 */
-	mutex_lock(&group->notification_mutex);
+	spin_lock(&group->notification_lock);
 	while (!fsnotify_notify_queue_is_empty(group)) {
 		fsn_event = fsnotify_remove_first_event(group);
 		if (!(fsn_event->mask & FAN_ALL_PERM_EVENTS)) {
-			mutex_unlock(&group->notification_mutex);
+			spin_unlock(&group->notification_lock);
 			fsnotify_destroy_event(group, fsn_event);
-			mutex_lock(&group->notification_mutex);
+			spin_lock(&group->notification_lock);
 		} else
 			FANOTIFY_PE(fsn_event)->response = FAN_ALLOW;
 	}
-	mutex_unlock(&group->notification_mutex);
+	spin_unlock(&group->notification_lock);
 
 	/* Response for all permission events it set, wakeup waiters */
 	wake_up(&group->fanotify_data.access_waitq);
@@ -423,10 +424,10 @@ static long fanotify_ioctl(struct file *file, unsigned int cmd, unsigned long ar
 
 	switch (cmd) {
 	case FIONREAD:
-		mutex_lock(&group->notification_mutex);
+		spin_lock(&group->notification_lock);
 		list_for_each_entry(fsn_event, &group->notification_list, list)
 			send_len += FAN_EVENT_METADATA_LEN;
-		mutex_unlock(&group->notification_mutex);
+		spin_unlock(&group->notification_lock);
 		ret = put_user(send_len, (int __user *) p);
 		break;
 	}