xen/privcmd: unregister xenstore notifier on module exit

Commit 453b8fb ("xen/privcmd: restrict usage in
unprivileged domU") added a xenstore notifier to defer setting the
restriction target until Xenstore is ready.

XEN_PRIVCMD can be built as a module, but privcmd_exit() leaves that
notifier behind. Balance the notifier lifecycle by unregistering it on
module exit.

This is harmless even if xenstore was already ready at registration
time and the notifier was never queued on the chain.

Fixes: 453b8fb ("xen/privcmd: restrict usage in unprivileged domU")
Signed-off-by: GuoHan Zhao <zhaoguohan@kylinos.cn>
Reviewed-by: Juergen Gross <jgross@suse.com>
Signed-off-by: Juergen Gross <jgross@suse.com>
Message-ID: <20260325120246.252899-1-zhaoguohan@kylinos.cn>

Author: GuoHan Zhao

drivers/xen/privcmd.c

@@ -1765,6 +1765,9 @@ static int __init privcmd_init(void)
 
 static void __exit privcmd_exit(void)
 {
+	if (!xen_initial_domain())
+		unregister_xenstore_notifier(&xenstore_notifier);
+
 	privcmd_ioeventfd_exit();
 	privcmd_irqfd_exit();
 	misc_deregister(&privcmd_dev);