fsnotify: Remove special handling of mark destruction on group shutdown

Currently we queue all marks for destruction on group shutdown and then
destroy them from fsnotify_destroy_group() instead from a worker thread
which is the usual path. However worker can already be processing some
list of marks to destroy so this does not make 100% all marks are really
destroyed by the time group is shut down. This isn't a big problem as
each mark holds group reference and thus group stays partially alive
until all marks are really freed but there's no point in complicating
our lives - just wait for the delayed work to be finished instead.
Reviewed-by: Miklos Szeredi <mszeredi@redhat.com>
Reviewed-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Jan Kara <jack@suse.cz>

fs/notify/fsnotify.h

@@ -36,10 +36,8 @@ static inline void fsnotify_clear_marks_by_mount(struct vfsmount *mnt)
 }
 /* prepare for freeing all marks associated with given group */
 extern void fsnotify_detach_group_marks(struct fsnotify_group *group);
-/*
- * wait for fsnotify_mark_srcu period to end and free all marks in destroy_list
- */
-extern void fsnotify_mark_destroy_list(void);
+/* Wait until all marks queued for destruction are destroyed */
+extern void fsnotify_wait_marks_destroyed(void);
 
 /*
  * update the dentry->d_flags of all of inode's children to indicate if inode cares

fs/notify/group.c

@@ -66,14 +66,16 @@ void fsnotify_destroy_group(struct fsnotify_group *group)
 	 */
 	fsnotify_group_stop_queueing(group);
 
-	/* clear all inode marks for this group, attach them to destroy_list */
+	/* Clear all marks for this group and queue them for destruction */
 	fsnotify_detach_group_marks(group);
 
 	/*
-	 * Wait for fsnotify_mark_srcu period to end and free all marks in
-	 * destroy_list
+	 * Wait until all marks get really destroyed. We could actually destroy
+	 * them ourselves instead of waiting for worker to do it, however that
+	 * would be racy as worker can already be processing some marks before
+	 * we even entered fsnotify_destroy_group().
 	 */
-	fsnotify_mark_destroy_list();
+	fsnotify_wait_marks_destroyed();
 
 	/*
 	 * Since we have waited for fsnotify_mark_srcu in

fs/notify/mark.c

@@ -703,7 +703,7 @@ void fsnotify_init_mark(struct fsnotify_mark *mark,
  * Destroy all marks in destroy_list, waits for SRCU period to finish before
  * actually freeing marks.
  */
-void fsnotify_mark_destroy_list(void)
+static void fsnotify_mark_destroy_workfn(struct work_struct *work)
 {
 	struct fsnotify_mark *mark, *next;
 	struct list_head private_destroy_list;
@@ -721,7 +721,8 @@ void fsnotify_mark_destroy_list(void)
 	}
 }
 
-static void fsnotify_mark_destroy_workfn(struct work_struct *work)
+/* Wait for all marks queued for destruction to be actually destroyed */
+void fsnotify_wait_marks_destroyed(void)
 {
-	fsnotify_mark_destroy_list();
+	flush_delayed_work(&reaper_work);
 }