[PATCH 3.15 020/109] xen/manage: fix potential deadlock when resuming the console

Greg Kroah-Hartman
2014-07-26T19:01:42Z

From: David Vrabel <david.vrabel@citrix.com>

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
drivers/xen/manage.c | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)

--- a/drivers/xen/manage.c
+++ b/drivers/xen/manage.c
@@ -109,7 +109,6 @@ static int xen_suspend(void *data)

if (!si->cancelled) {
xen_irq_resume();
- xen_console_resume();
xen_timer_resume();
}

@@ -166,6 +165,10 @@ 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();
+
raw_notifier_call_chain(&xen_resume_notifier, 0, NULL);

dpm_resume_start(si.cancelled ? PMSG_THAW : PMSG_RESTORE);