eventfs: Use list_add_tail_rcu() for SRCU-protected children list

[ Upstream commit f67950b2887fa10df50c4317a1fe98a65bc6875b ]

Commit d260327 ("eventfs: Use list_del_rcu() for SRCU protected
list variable") converted the removal side to pair with the
list_for_each_entry_srcu() walker in eventfs_iterate(). The insertion
in eventfs_create_dir() was left as a plain list_add_tail(), which on
weakly-ordered architectures can expose a new entry to the SRCU reader
before its list pointers and fields are observable.

Use list_add_tail_rcu() so the publication pairs with the existing
list_del_rcu() and list_for_each_entry_srcu().

Fixes: 43aa6f9 ("eventfs: Get rid of dentry pointers without refcounts")
Cc: stable@vger.kernel.org
Link: https://patch.msgid.link/20260418152251.199343-1-devnexen@gmail.com
Signed-off-by: David Carlier <devnexen@gmail.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
[ adapted scoped_guard(mutex, &eventfs_mutex) block to explicit mutex_lock()/mutex_unlock() pair ]
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: devnexen

fs/tracefs/event_inode.c

@@ -732,7 +732,7 @@ struct eventfs_inode *eventfs_create_dir(const char *name, struct eventfs_inode
 
 	mutex_lock(&eventfs_mutex);
 	if (!parent->is_freed)
-		list_add_tail(&ei->list, &parent->children);
+		list_add_tail_rcu(&ei->list, &parent->children);
 	mutex_unlock(&eventfs_mutex);
 
 	/* Was the parent freed? */