xen/manage: unwind partial shutdown watcher setup on error

setup_shutdown_watcher() registers shutdown_watch first, then the sysrq
watch, and finally publishes the supported feature-* nodes in xenstore.
If sysrq watch registration fails, or xenbus_printf() fails after one or
more feature nodes were created, the function returns immediately without
undoing the earlier setup.

This leaves the system in a partially initialized state, with registered
watches and/or stale xenstore entries despite the function reporting
failure.

Unwind the partial setup before returning an error by unregistering any
watches that were already registered and removing feature nodes that were
already published.

Signed-off-by: GuoHan Zhao <zhaoguohan@kylinos.cn>
Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>
Signed-off-by: Juergen Gross <jgross@suse.com>
Message-ID: <20260407022443.12971-1-zhaoguohan@kylinos.cn>

Author: GuoHan Zhao

drivers/xen/manage.c

@@ -343,12 +343,11 @@ static int setup_shutdown_watcher(void)
 		return err;
 	}
 
-
 #ifdef CONFIG_MAGIC_SYSRQ
 	err = register_xenbus_watch(&sysrq_watch);
 	if (err) {
 		pr_err("Failed to set sysrq watcher\n");
-		return err;
+		goto err_unregister_shutdown;
 	}
 #endif
 
@@ -361,11 +360,26 @@ static int setup_shutdown_watcher(void)
 		if (err) {
 			pr_err("%s: Error %d writing %s\n", __func__,
 				err, node);
-			return err;
+			goto err_remove_features;
 		}
 	}
 
 	return 0;
+
+err_remove_features:
+	while (--idx >= 0) {
+		if (!shutdown_handlers[idx].flag)
+			continue;
+		snprintf(node, FEATURE_PATH_SIZE, "feature-%s",
+			 shutdown_handlers[idx].command);
+		xenbus_rm(XBT_NIL, "control", node);
+	}
+#ifdef CONFIG_MAGIC_SYSRQ
+	unregister_xenbus_watch(&sysrq_watch);
+err_unregister_shutdown:
+#endif
+	unregister_xenbus_watch(&shutdown_watch);
+	return err;
 }
 
 static int shutdown_event(struct notifier_block *notifier,