convert tracefs

A mix of persistent and non-persistent dentries in there. Strictly
speaking, no need for kill_litter_super() anyway - it pins an internal
mount whenever a persistent dentry is created, so at fs shutdown time
there won't be any to deal with.

However, let's make it explicit - replace d_instantiate() with
d_make_persistent() + dput() (the latter in tracefs_end_creating(),
where it folds with inode_unlock() into simple_done_creating())
for dentries we want persistent and have d_make_discardable() done
either by simple_recursive_removal() (used by tracefs_remove())
or explicitly in eventfs_remove_events_dir().

Acked-by: Steven Rostedt (Google) <[e-mail]>
Signed-off-by: Al Viro <[e-mail]>

fs/tracefs/event_inode.c

···
 	 * something not worth much. Keeping directory links at 1
 	 * tells userspace not to trust the link number.
 	 */
-	d_instantiate(dentry, inode);
+	d_make_persistent(dentry, inode);
 	/* The dentry of the "events" parent does keep track though */
 	inc_nlink(dentry->d_parent->d_inode);
 	fsnotify_mkdir(dentry->d_parent->d_inode, dentry);
···
 	 * and destroyed dynamically.
 	 */
 	d_invalidate(dentry);
-	dput(dentry);
+	d_make_discardable(dentry);
 }

fs/tracefs/inode.c

···
 	.name =		"tracefs",
 	.init_fs_context = tracefs_init_fs_context,
 	.parameters	= tracefs_param_specs,
-	.kill_sb =	kill_litter_super,
+	.kill_sb =	kill_anon_super,
 };
 MODULE_ALIAS_FS("tracefs");
 
···
 
 struct dentry *tracefs_failed_creating(struct dentry *dentry)
 {
-	inode_unlock(d_inode(dentry->d_parent));
-	dput(dentry);
+	simple_done_creating(dentry);
 	simple_release_fs(&tracefs_mount, &tracefs_mount_count);
 	return NULL;
 }
 
 struct dentry *tracefs_end_creating(struct dentry *dentry)
 {
-	inode_unlock(d_inode(dentry->d_parent));
-	return dentry;
+	simple_done_creating(dentry);
+	return dentry;	// borrowed
 }
 
 /* Find the inode that this will use for default */
···
 	inode->i_private = data;
 	inode->i_uid = d_inode(dentry->d_parent)->i_uid;
 	inode->i_gid = d_inode(dentry->d_parent)->i_gid;
-	d_instantiate(dentry, inode);
+	d_make_persistent(dentry, inode);
 	fsnotify_create(d_inode(dentry->d_parent), dentry);
 	return tracefs_end_creating(dentry);
 }
···
 
 	/* directory inodes start off with i_nlink == 2 (for "." entry) */
 	inc_nlink(inode);
-	d_instantiate(dentry, inode);
+	d_make_persistent(dentry, inode);
 	inc_nlink(d_inode(dentry->d_parent));
 	fsnotify_mkdir(d_inode(dentry->d_parent), dentry);
 	return tracefs_end_creating(dentry);