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>

5 files changed, 41 insertions, 37 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;
         }
diff --git a/fs/notify/group.c b/fs/notify/group.c
index b47f7cfdcaa4..fbe3cbebec16 100644
--- a/fs/notify/group.c
+++ b/fs/notify/group.c
@@ -45,9 +45,9 @@ static void fsnotify_final_destroy_group(struct fsnotify_group *group)
  */
 void fsnotify_group_stop_queueing(struct fsnotify_group *group)
 {
-        mutex_lock(&group->notification_mutex);
+        spin_lock(&group->notification_lock);
         group->shutdown = true;
-        mutex_unlock(&group->notification_mutex);
+        spin_unlock(&group->notification_lock);
 }
 
 /*
@@ -125,7 +125,7 @@ struct fsnotify_group *fsnotify_alloc_group(const struct fsnotify_ops *ops)
         atomic_set(&group->refcnt, 1);
         atomic_set(&group->num_marks, 0);
 
-        mutex_init(&group->notification_mutex);
+        spin_lock_init(&group->notification_lock);
         INIT_LIST_HEAD(&group->notification_list);
         init_waitqueue_head(&group->notification_waitq);
         group->max_events = UINT_MAX;
diff --git a/fs/notify/inotify/inotify_user.c b/fs/notify/inotify/inotify_user.c
index b8d08d0d0a4d..69d1ea3d292a 100644
--- a/fs/notify/inotify/inotify_user.c
+++ b/fs/notify/inotify/inotify_user.c
@@ -115,10 +115,10 @@ static unsigned int inotify_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;
 }
@@ -138,7 +138,7 @@ static int round_event_name_len(struct fsnotify_event *fsn_event)
  * enough to fit in "count". Return an error pointer if
  * 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)
@@ -157,7 +157,7 @@ static struct fsnotify_event *get_one_event(struct fsnotify_group *group,
         if (event_size > 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 */
         fsnotify_remove_first_event(group);
 
@@ -234,9 +234,9 @@ static ssize_t inotify_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);
 
                 pr_debug("%s: group=%p kevent=%p\n", __func__, group, kevent);
 
@@ -300,13 +300,13 @@ static long inotify_ioctl(struct file *file, unsigned int cmd,
 
         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 += sizeof(struct inotify_event);
                         send_len += round_event_name_len(fsn_event);
                 }
-                mutex_unlock(&group->notification_mutex);
+                spin_unlock(&group->notification_lock);
                 ret = put_user(send_len, (int __user *) p);
                 break;
         }
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);
 }
 
 /*
diff --git a/include/linux/fsnotify_backend.h b/include/linux/fsnotify_backend.h
index 7268ed076be8..0713e873b1c9 100644
--- a/include/linux/fsnotify_backend.h
+++ b/include/linux/fsnotify_backend.h
@@ -135,7 +135,7 @@ struct fsnotify_group {
         const struct fsnotify_ops *ops; /* how this group handles things */
 
         /* needed to send notification to userspace */
-        struct mutex notification_mutex;        /* protect the notification_list */
+        spinlock_t notification_lock;           /* protect the notification_list */
         struct list_head notification_list;     /* list of event_holder this group needs to send to userspace */
         wait_queue_head_t notification_waitq;   /* read() on the notification file blocks on this waitq */
         unsigned int q_len;                     /* events on the queue */