PV-on-HVM: More carefully synchronise with APs when putting them to

sleep in a spin loop.
Signed-off-by: Keir Fraser <keir@xensource.com>

1 files changed, 27 insertions, 7 deletions

diff --git a/unmodified_drivers/linux-2.6/platform-pci/machine_reboot.c b/unmodified_drivers/linux-2.6/platform-pci/machine_reboot.c
index c6b1f91b7f..15ceef8da6 100644
--- a/unmodified_drivers/linux-2.6/platform-pci/machine_reboot.c
+++ b/unmodified_drivers/linux-2.6/platform-pci/machine_reboot.c
@@ -6,21 +6,32 @@
 #include "platform-pci.h"
 #include <asm/hypervisor.h>
 
+struct ap_suspend_info {
+	int      do_spin;
+	atomic_t nr_spinning;
+};
+
 /*
  * Spinning prevents, for example, APs touching grant table entries while
  * the shared grant table is not mapped into the address space imemdiately
  * after resume.
  */
-static void ap_suspend(void *_ap_spin)
+static void ap_suspend(void *_info)
 {
-	int *ap_spin = _ap_spin;
+	struct ap_suspend_info *info = _info;
 
 	BUG_ON(!irqs_disabled());
 
-	while (*ap_spin) {
+	atomic_inc(&info->nr_spinning);
+	mb();
+
+	while (info->do_spin) {
 		cpu_relax();
 		HYPERVISOR_yield();
 	}
+
+	mb();
+	atomic_dec(&info->nr_spinning);
 }
 
 static int bp_suspend(void)
@@ -42,7 +53,8 @@ static int bp_suspend(void)
 
 int __xen_suspend(int fast_suspend)
 {
-	int err, suspend_cancelled, ap_spin;
+	int err, suspend_cancelled, nr_cpus;
+	struct ap_suspend_info info;
 
 	xenbus_suspend();
 
@@ -51,22 +63,30 @@ int __xen_suspend(int fast_suspend)
 	/* Prevent any races with evtchn_interrupt() handler. */
 	disable_irq(xen_platform_pdev->irq);
 
-	ap_spin = 1;
+	info.do_spin = 1;
+	atomic_set(&info.nr_spinning, 0);
 	smp_mb();
 
-	err = smp_call_function(ap_suspend, &ap_spin, 0, 0);
+	nr_cpus = num_online_cpus() - 1;
+
+	err = smp_call_function(ap_suspend, &info, 0, 0);
 	if (err < 0) {
 		preempt_enable();
 		xenbus_suspend_cancel();
 		return err;
 	}
 
+	while (atomic_read(&info.nr_spinning) != nr_cpus)
+		cpu_relax();
+
 	local_irq_disable();
 	suspend_cancelled = bp_suspend();
 	local_irq_enable();
 
 	smp_mb();
-	ap_spin = 0;
+	info.do_spin = 0;
+	while (atomic_read(&info.nr_spinning) != 0)
+		cpu_relax();
 
 	enable_irq(xen_platform_pdev->irq);