linux-kernel - [PATCH 3.2 21/94] xen/manage: fix potential deadlock when resuming the console

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Message-ID: <lsq.1407170911.274536002@decadent.org.uk>
Date:	Mon, 04 Aug 2014 17:48:31 +0100
From:	Ben Hutchings <ben@...adent.org.uk>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:	akpm@...ux-foundation.org,
	"Boris Ostrovsky" <boris.ostrovsky@...cle.com>,
	"David Vrabel" <david.vrabel@...rix.com>
Subject: [PATCH 3.2 21/94] xen/manage: fix potential deadlock when
 resuming the console

3.2.62-rc1 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>
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 drivers/xen/manage.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

--- 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) {

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