eventfs: Remove "is_freed" union with rcu head

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: 63940449 ("eventfs: Implement eventfs lookup, read, open functions")
Reviewed-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

fs/tracefs/event_inode.c

@@ -824,6 +824,8 @@ static void eventfs_remove_rec(struct eventfs_inode *ei, struct list_head *head,
 		eventfs_remove_rec(ei_child, head, level + 1);
 	}
 
+	ei->is_freed = 1;
+
 	list_del_rcu(&ei->list);
 	list_add_tail(&ei->del_list, head);
 }

fs/tracefs/internal.h

@@ -23,6 +23,7 @@ struct tracefs_inode {
  * @d_parent:   pointer to the parent's dentry
  * @d_children: The array of dentries to represent the files when created
  * @data:	The private data to pass to the callbacks
+ * @is_freed:	Flag set if the eventfs is on its way to be freed
  * @nr_entries: The number of items in @entries
  */
 struct eventfs_inode {
@@ -38,14 +39,13 @@ struct eventfs_inode {
 	 * Union - used for deletion
 	 * @del_list:	list of eventfs_inode to delete
 	 * @rcu:	eventfs_inode 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;
 	};
-	int				nr_entries;
+	unsigned int			is_freed:1;
+	unsigned int			nr_entries:31;
 };
 
 static inline struct tracefs_inode *get_tracefs(const struct inode *inode)