xen/manage: Always freeze/thaw processes when suspend/resuming

commit 61a734d3 upstream.

Always freeze processes when suspending and thaw processes when resuming
to prevent a race noticeable with HVM guests.

This prevents a deadlock where the khubd kthread (which is designed to
be freezable) acquires a usb device lock and then tries to allocate
memory which requires the disk which hasn't been resumed yet.
Meanwhile, the xenwatch thread deadlocks waiting for the usb device
lock.

Freezing processes fixes this because the khubd thread is only thawed
after the xenwatch thread finishes resuming all the devices.
Signed-off-by: Ross Lagerwall <ross.lagerwall@citrix.com>
Signed-off-by: David Vrabel <david.vrabel@citrix.com>
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

drivers/xen/manage.c

@@ -108,16 +108,11 @@ static void do_suspend(void)
 
 	shutting_down = SHUTDOWN_SUSPEND;
 
-#ifdef CONFIG_PREEMPT
-	/* If the kernel is preemptible, we need to freeze all the processes
-	   to prevent them from being in the middle of a pagetable update
-	   during suspend. */
 	err = freeze_processes();
 	if (err) {
 		printk(KERN_ERR "xen suspend: freeze failed %d\n", err);
 		goto out;
 	}
-#endif
 
 	err = dpm_suspend_start(PMSG_FREEZE);
 	if (err) {
@@ -172,10 +167,8 @@ static void do_suspend(void)
 	clock_was_set();
 
 out_thaw:
-#ifdef CONFIG_PREEMPT
 	thaw_processes();
 out:
-#endif
 	shutting_down = SHUTDOWN_INVALID;
 }
 #endif	/* CONFIG_HIBERNATE_CALLBACKS */