eventfs: Remove "is_freed" union with rcu head

commit f2f4963 upstream

The eventfs_inode->is_freed was a union with the rcu_head with the
assumption that when it was on the srcu list the head would contain a
pointer which would make "is_freed" true. But that was a wrong assumption
as the rcu head is a single link list where the last element is NULL.

Instead, split the nr_entries integer so that "is_freed" is one bit and
the nr_entries is the next 31 bits. As there shouldn't be more than 10
(currently there's at most 5 to 7 depending on the config), this should
not be a problem.

Link: https://lkml.kernel.org/r/20231101172649.049758712@goodmis.org

Cc: stable@vger.kernel.org
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Ajay Kaher <akaher@vmware.com>
Fixes: 6394044 ("eventfs: Implement eventfs lookup, read, open functions")
Reviewed-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

fs/tracefs/event_inode.c

@@ -38,6 +38,7 @@ struct eventfs_inode {
  * @fop:	file_operations for file or directory
  * @iop:	inode_operations for file or directory
  * @data:	something that the caller will want to get to later on
+ * @is_freed:	Flag set if the eventfs is on its way to be freed
  * @mode:	the permission that the file or directory should have
  */
 struct eventfs_file {
@@ -52,15 +53,14 @@ struct eventfs_file {
 	 * Union - used for deletion
 	 * @del_list:	list of eventfs_file to delete
 	 * @rcu:	eventfs_file to delete in RCU
-	 * @is_freed:	node is freed if one of the above is set
 	 */
 	union {
 		struct list_head	del_list;
 		struct rcu_head		rcu;
-		unsigned long		is_freed;
 	};
 	void				*data;
-	umode_t				mode;
+	unsigned int			is_freed:1;
+	unsigned int			mode:31;
 };
 
 static DEFINE_MUTEX(eventfs_mutex);
@@ -814,6 +814,8 @@ static void eventfs_remove_rec(struct eventfs_file *ef, struct list_head *head,
 		}
 	}
 
+	ef->is_freed = 1;
+
 	list_del_rcu(&ef->list);
 	list_add_tail(&ef->del_list, head);
 }