xen/acpi: upload PM state from init-domain to Xen

This was broken in commit cd97988 ("xen/acpi-processor:
fix enabling interrupts on syscore_resume"). do_suspend (from
xen/manage.c) and thus xen_resume_notifier never get called on
the initial-domain at resume (it is if running as guest.)

The rationale for the breaking change was that upload_pm_data()
potentially does blocking work in syscore_resume(). This patch
addresses the original issue by scheduling upload_pm_data() to
execute in workqueue context.

Cc: Stanislaw Gruszka <sgruszka@redhat.com>
Cc: stable@vger.kernel.org
Based-on-patch-by: Konrad Wilk <konrad.wilk@oracle.com>
Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Reviewed-by: Stanislaw Gruszka <sgruszka@redhat.com>
Signed-off-by: Ankur Arora <ankur.a.arora@oracle.com>
Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>

drivers/xen/xen-acpi-processor.c

@@ -27,10 +27,10 @@
 #include <linux/init.h>
 #include <linux/module.h>
 #include <linux/types.h>
+#include <linux/syscore_ops.h>
 #include <linux/acpi.h>
 #include <acpi/processor.h>
 #include <xen/xen.h>
-#include <xen/xen-ops.h>
 #include <xen/interface/platform.h>
 #include <asm/xen/hypercall.h>
 
@@ -466,15 +466,33 @@ static int xen_upload_processor_pm_data(void)
 	return rc;
 }
 
-static int xen_acpi_processor_resume(struct notifier_block *nb,
-				     unsigned long action, void *data)
+static void xen_acpi_processor_resume_worker(struct work_struct *dummy)
 {
+	int rc;
+
 	bitmap_zero(acpi_ids_done, nr_acpi_bits);
-	return xen_upload_processor_pm_data();
+
+	rc = xen_upload_processor_pm_data();
+	if (rc != 0)
+		pr_info("ACPI data upload failed, error = %d\n", rc);
+}
+
+static void xen_acpi_processor_resume(void)
+{
+	static DECLARE_WORK(wq, xen_acpi_processor_resume_worker);
+
+	/*
+	 * xen_upload_processor_pm_data() calls non-atomic code.
+	 * However, the context for xen_acpi_processor_resume is syscore
+	 * with only the boot CPU online and in an atomic context.
+	 *
+	 * So defer the upload for some point safer.
+	 */
+	schedule_work(&wq);
 }
 
-struct notifier_block xen_acpi_processor_resume_nb = {
-	.notifier_call = xen_acpi_processor_resume,
+static struct syscore_ops xap_syscore_ops = {
+	.resume	= xen_acpi_processor_resume,
 };
 
 static int __init xen_acpi_processor_init(void)
@@ -527,7 +545,7 @@ static int __init xen_acpi_processor_init(void)
 	if (rc)
 		goto err_unregister;
 
-	xen_resume_notifier_register(&xen_acpi_processor_resume_nb);
+	register_syscore_ops(&xap_syscore_ops);
 
 	return 0;
 err_unregister:
@@ -544,7 +562,7 @@ static void __exit xen_acpi_processor_exit(void)
 {
 	int i;
 
-	xen_resume_notifier_unregister(&xen_acpi_processor_resume_nb);
+	unregister_syscore_ops(&xap_syscore_ops);
 	kfree(acpi_ids_done);
 	kfree(acpi_id_present);
 	kfree(acpi_id_cst_present);