xen/acpi-processor: fix enabling interrupts on syscore_resume

syscore->resume() callback is expected to do not enable interrupts,
it generates warning like below otherwise:

[ 9386.365390] WARNING: CPU: 0 PID: 6733 at drivers/base/syscore.c:104 syscore_resume+0x9a/0xe0()
[ 9386.365403] Interrupts enabled after xen_acpi_processor_resume+0x0/0x34 [xen_acpi_processor]
...
[ 9386.365429] Call Trace:
[ 9386.365434] [<ffffffff81667a8b>] dump_stack+0x45/0x56
[ 9386.365437] [<ffffffff8106921d>] warn_slowpath_common+0x7d/0xa0
[ 9386.365439] [<ffffffff8106928c>] warn_slowpath_fmt+0x4c/0x50
[ 9386.365442] [<ffffffffa0261bb0>] ? xen_upload_processor_pm_data+0x300/0x300 [xen_acpi_processor]
[ 9386.365443] [<ffffffff814055fa>] syscore_resume+0x9a/0xe0
[ 9386.365445] [<ffffffff810aef42>] suspend_devices_and_enter+0x402/0x470
[ 9386.365447] [<ffffffff810af128>] pm_suspend+0x178/0x260

On xen_acpi_processor_resume() we call various procedures, which are
non atomic and can enable interrupts. To prevent the issue introduce
separate resume notify called after we enable interrupts on resume
and before we call other drivers resume callbacks.

Signed-off-by: Stanislaw Gruszka <[e-mail]>
Signed-off-by: Konrad Rzeszutek Wilk <[e-mail]>

drivers/xen/manage.c

···
 	void (*post)(int cancelled);
 };
 
+static RAW_NOTIFIER_HEAD(xen_resume_notifier);
+
+void xen_resume_notifier_register(struct notifier_block *nb)
+{
+	raw_notifier_chain_register(&xen_resume_notifier, nb);
+}
+EXPORT_SYMBOL_GPL(xen_resume_notifier_register);
+
+void xen_resume_notifier_unregister(struct notifier_block *nb)
+{
+	raw_notifier_chain_unregister(&xen_resume_notifier, nb);
+}
+EXPORT_SYMBOL_GPL(xen_resume_notifier_unregister);
+
 #ifdef CONFIG_HIBERNATE_CALLBACKS
 static void xen_hvm_post_suspend(int cancelled)
 {
···
 	}
 
 	err = stop_machine(xen_suspend, &si, cpumask_of(0));
+
+	raw_notifier_call_chain(&xen_resume_notifier, 0, NULL);
 
 	dpm_resume_start(si.cancelled ? PMSG_THAW : PMSG_RESTORE);
 

drivers/xen/xen-acpi-processor.c

···
 #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>
 
···
 	return rc;
 }
 
-static void xen_acpi_processor_resume(void)
+static int xen_acpi_processor_resume(struct notifier_block *nb,
+				     unsigned long action, void *data)
 {
 	bitmap_zero(acpi_ids_done, nr_acpi_bits);
-	xen_upload_processor_pm_data();
+	return xen_upload_processor_pm_data();
 }
 
-static struct syscore_ops xap_syscore_ops = {
-	.resume	= xen_acpi_processor_resume,
+struct notifier_block xen_acpi_processor_resume_nb = {
+	.notifier_call = xen_acpi_processor_resume,
 };
 
 static int __init xen_acpi_processor_init(void)
···
 	if (rc)
 		goto err_unregister;
 
-	register_syscore_ops(&xap_syscore_ops);
+	xen_resume_notifier_register(&xen_acpi_processor_resume_nb);
 
 	return 0;
 err_unregister:
···
 {
 	int i;
 
-	unregister_syscore_ops(&xap_syscore_ops);
+	xen_resume_notifier_unregister(&xen_acpi_processor_resume_nb);
 	kfree(acpi_ids_done);
 	kfree(acpi_id_present);
 	kfree(acpi_id_cst_present);

include/xen/xen-ops.h

···
 #define INCLUDE_XEN_OPS_H
 
 #include <linux/percpu.h>
+#include <linux/notifier.h>
 #include <asm/xen/interface.h>
 
 DECLARE_PER_CPU(struct vcpu_info *, xen_vcpu);
···
 
 void xen_timer_resume(void);
 void xen_arch_resume(void);
+
+void xen_resume_notifier_register(struct notifier_block *nb);
+void xen_resume_notifier_unregister(struct notifier_block *nb);
 
 int xen_setup_shutdown_event(void);