xen/manage: fix potential deadlock when resuming the console

commit 1b647823 upstream.

Calling xen_console_resume() in xen_suspend() causes a warning because
it locks irq_mapping_update_lock (a mutex) and this may sleep.  If a
userspace process is using the evtchn device then this mutex may be
locked at the point of the stop_machine() call and
xen_console_resume() would then deadlock.

Resuming the console after stop_machine() returns avoids this
deadlock.
Signed-off-by: David Vrabel <david.vrabel@citrix.com>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

drivers/xen/manage.c

@@ -93,7 +93,6 @@ static int xen_suspend(void *data)
 
 	if (!si->cancelled) {
 		xen_irq_resume();
-		xen_console_resume();
 		xen_timer_resume();
 	}
 
@@ -149,6 +148,10 @@ static void do_suspend(void)
 
 	err = stop_machine(xen_suspend, &si, cpumask_of(0));
 
+	/* Resume console as early as possible. */
+	if (!si.cancelled)
+		xen_console_resume();
+
 	dpm_resume_noirq(si.cancelled ? PMSG_THAW : PMSG_RESTORE);
 
 	if (err) {