xen/manage: fix potential deadlock when resuming the console

commit 1b6478231c6f5f844185acb32045cf195028cfce 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>

diff --git a/drivers/xen/manage.c b/drivers/xen/manage.c
index ce4fa08..c8af7e5 100644 (file)
--- a/drivers/xen/manage.c
+++ b/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) {