linux-kernel - [PATCH 3.11 004/137] xen/manage: fix potential deadlock when resuming the console

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Message-Id: <1408354398-10226-5-git-send-email-luis.henriques@canonical.com>
Date:	Mon, 18 Aug 2014 10:31:05 +0100
From:	Luis Henriques <luis.henriques@...onical.com>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	kernel-team@...ts.ubuntu.com
Cc:	David Vrabel <david.vrabel@...rix.com>,
	Luis Henriques <luis.henriques@...onical.com>
Subject: [PATCH 3.11 004/137] xen/manage: fix potential deadlock when resuming the console

3.11.10.15 -stable review patch.  If anyone has any objections, please let me know.

------------------

From: David Vrabel <david.vrabel@...rix.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@...rix.com>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@...cle.com>
[ luis: backported to 3.11: adjusted context ]
Signed-off-by: Luis Henriques <luis.henriques@...onical.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 624e8dc24532..0bc8086064ca 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

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