[3.13.y.z extended stable] Patch "xen/manage: fix potential deadlock when resuming the console" has been added to staging queue

[Kamal Mostafa]

This is a note to let you know that I have just added a patch titled

    xen/manage: fix potential deadlock when resuming the console

to the linux-3.13.y-queue branch of the 3.13.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.13.y-queue

This patch is scheduled to be released in version 3.13.11.6.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.13.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

------

>From f88169fedd5e3530b687bfe01f5907b981ef6b4f Mon Sep 17 00:00:00 2001
From: David Vrabel <david.vrabel at citrix.com>
Date: Wed, 2 Jul 2014 17:25:23 +0100
Subject: 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 at citrix.com>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky at oracle.com>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 drivers/xen/manage.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/xen/manage.c b/drivers/xen/manage.c
index 624e8dc..0bc8086 100644
--- a/drivers/xen/manage.c
+++ b/drivers/xen/manage.c
@@ -95,7 +95,6 @@ static int xen_suspend(void *data)

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

@@ -152,6 +151,10 @@ 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_start(si.cancelled ? PMSG_THAW : PMSG_RESTORE);

 	if (err) {
--
1.9.1