serialize suspend-resume process

diff -r c2850a7f279d drivers/xen/core/reboot.c
@@ -11,6 +11,7 @@
 #include <linux/kmod.h>
 #include <linux/slab.h>
 #include <linux/workqueue.h>
+#include <linux/kthread.h>
 
 #ifdef HAVE_XEN_PLATFORM_COMPAT_H
 #include <xen/platform-compat.h>

@@ -20,8 +21,6 @@ MODULE_LICENSE("Dual BSD/GPL");
 
 #define SHUTDOWN_INVALID  -1
 #define SHUTDOWN_POWEROFF  0
-#define SHUTDOWN_SUSPEND   2
-#define SHUTDOWN_RESUMING  3
 #define SHUTDOWN_HALT      4
 
 /* Ignore multiple shutdown requests. */

@@ -32,6 +31,11 @@ static int fast_suspend;
 
 static void __shutdown_handler(void *unused);
 static DECLARE_WORK(shutdown_work, __shutdown_handler, NULL);
+
+static struct suspend_info {
+        struct semaphore nrequest; /* no. of suspend reqs */
+        atomic_t         resuming; /* is domain resuming ? */
+} suspend_info;
 
 int __xen_suspend(int fast_suspend, void (*resume_notifier)(void));
 

@@ -62,58 +66,11 @@ static int shutdown_process(void *__unus
 	return 0;
 }
 
-static void xen_resume_notifier(void)
-{
-	int old_state = xchg(&shutting_down, SHUTDOWN_RESUMING);
-	BUG_ON(old_state != SHUTDOWN_SUSPEND);
-}
-
-static int xen_suspend(void *__unused)
-{
-	int err, old_state;
-
-	daemonize("suspend");
-	err = set_cpus_allowed(current, cpumask_of_cpu(0));
-	if (err) {
-		printk(KERN_ERR "Xen suspend can't run on CPU0 (%d)\n", err);
-		goto fail;
-	}
-
-	do {
-		err = __xen_suspend(fast_suspend, xen_resume_notifier);
-		if (err) {
-			printk(KERN_ERR "Xen suspend failed (%d)\n", err);
-			goto fail;
-		}
-		old_state = cmpxchg(
-			&shutting_down, SHUTDOWN_RESUMING, SHUTDOWN_INVALID);
-	} while (old_state == SHUTDOWN_SUSPEND);
-
-	switch (old_state) {
-	case SHUTDOWN_INVALID:
-	case SHUTDOWN_SUSPEND:
-		BUG();
-	case SHUTDOWN_RESUMING:
-		break;
-	default:
-		schedule_work(&shutdown_work);
-		break;
-	}
-
-	return 0;
-
- fail:
-	old_state = xchg(&shutting_down, SHUTDOWN_INVALID);
-	BUG_ON(old_state != SHUTDOWN_SUSPEND);
-	return 0;
-}
-
 static void __shutdown_handler(void *unused)
 {
 	int err;
 
-	err = kernel_thread((shutting_down == SHUTDOWN_SUSPEND) ?
-			    xen_suspend : shutdown_process,
+	err = kernel_thread(shutdown_process,
 			    NULL, CLONE_FS | CLONE_FILES);
 
 	if (err < 0) {

@@ -131,8 +88,8 @@ static void shutdown_handler(struct xenb
 	struct xenbus_transaction xbt;
 	int err, old_state, new_state = SHUTDOWN_INVALID;
 
-	if ((shutting_down != SHUTDOWN_INVALID) &&
-	    (shutting_down != SHUTDOWN_RESUMING))
+	if ((shutting_down != SHUTDOWN_INVALID) ||
+            atomic_read(&suspend_info.resuming))
 		return;
 
  again:

@@ -155,12 +112,12 @@ static void shutdown_handler(struct xenb
 		goto again;
 	}
 
-	if (strcmp(str, "poweroff") == 0)
-		new_state = SHUTDOWN_POWEROFF;
+        if (strcmp(str, "suspend") == 0)
+                up(&suspend_info.nrequest); /* backward compatibility */
 	else if (strcmp(str, "reboot") == 0)
 		ctrl_alt_del();
-	else if (strcmp(str, "suspend") == 0)
-		new_state = SHUTDOWN_SUSPEND;
+	else if (strcmp(str, "poweroff") == 0)
+		new_state = SHUTDOWN_POWEROFF;
 	else if (strcmp(str, "halt") == 0)
 		new_state = SHUTDOWN_HALT;
 	else

@@ -168,10 +125,8 @@ static void shutdown_handler(struct xenb
 
 	if (new_state != SHUTDOWN_INVALID) {
 		old_state = xchg(&shutting_down, new_state);
-		if (old_state == SHUTDOWN_INVALID)
-			schedule_work(&shutdown_work);
-		else
-			BUG_ON(old_state != SHUTDOWN_RESUMING);
+                BUG_ON(old_state != SHUTDOWN_INVALID);
+                schedule_work(&shutdown_work);
 	}
 
 	kfree(str);

@@ -218,10 +173,41 @@ static struct xenbus_watch sysrq_watch =
 	.callback = sysrq_handler
 };
 
+static void suspend_resume_notifier(void)
+{
+        atomic_set(&suspend_info.resuming, 1);
+        return;
+}
+
+static int suspend_machine(void *unused)
+{
+        int err = 0;
+        struct sched_param param = { .sched_priority = MAX_RT_PRIO-1 };
+
+        err = set_cpus_allowed(current, cpumask_of_cpu(0));
+        if (err) {
+                printk(KERN_ERR "Suspend thread couldn't switch to CPU0 (%d)\n", err);
+                return err;
+        }
+
+        sched_setscheduler(current, SCHED_FIFO, &param);
+
+        while (1) {
+                /* decrement no. of suspend requests */
+                down(&suspend_info.nrequest);
+
+                err = __xen_suspend(fast_suspend, &suspend_resume_notifier);
+                if (err)
+                        printk(KERN_ERR "Domain suspend failed (%d)\n", err);
+
+                atomic_set(&suspend_info.resuming, 0);
+        }
+}
+
 static irqreturn_t suspend_int(int irq, void* dev_id, struct pt_regs *ptregs)
 {
-	shutting_down = SHUTDOWN_SUSPEND;
-	schedule_work(&shutdown_work);
+        /* increment no. of suspend requests */
+        up(&suspend_info.nrequest);
 
 	return IRQ_HANDLED;
 }

@@ -251,6 +237,7 @@ static int setup_shutdown_watcher(void)
 static int setup_shutdown_watcher(void)
 {
 	int err;
+        struct task_struct *t = NULL;
 
 	xenbus_scanf(XBT_NIL, "control",
 		     "platform-feature-multiprocessor-suspend",

@@ -267,6 +254,15 @@ static int setup_shutdown_watcher(void)
 		printk(KERN_ERR "Failed to set sysrq watcher\n");
 		return err;
 	}
+
+        sema_init(&suspend_info.nrequest, 0);
+        atomic_set(&suspend_info.resuming, 0);
+        t = kthread_create(suspend_machine, &suspend_info, "ksuspend");
+        if (IS_ERR(t)) {
+                printk(KERN_ERR "Suspend thread creation failed\n");
+                return PTR_ERR(t);
+        }
+        wake_up_process(t);
 
 	/* suspend event channel */
 	err = setup_suspend_evtchn();

diff -r 44e3ace9a1f1 drivers/xen/core/reboot.c
@@ -108,6 +116,31 @@ static int xen_suspend(void *__unused)
 	return 0;
 }
 
+static void switch_shutdown_state(int new_state)
+{
+	int prev_state, old_state = SHUTDOWN_INVALID;
+
+	/* We only drive shutdown_state into an active state. */
+	if (new_state == SHUTDOWN_INVALID)
+		return;
+
+	do {
+		/* We drop this transition if already in an active state. */
+		if ((old_state != SHUTDOWN_INVALID) &&
+		    (old_state != SHUTDOWN_RESUMING))
+			return;
+		/* Attempt to transition. */
+		prev_state = old_state;
+		old_state = cmpxchg(&shutting_down, old_state, new_state);
+	} while (old_state != prev_state);
+
+	/* Either we kick off the work, or we leave it to xen_suspend(). */
+	if (old_state == SHUTDOWN_INVALID)
+		schedule_work(&shutdown_work);
+	else
+		BUG_ON(old_state != SHUTDOWN_RESUMING);
+}
+
 static void __shutdown_handler(void *unused)
 {
 	int err;