linux-kernel - [v2.6.34-stable 080/213] clockevents: Don't allow dummy broadcast timers

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Message-ID: <1391630568-49251-81-git-send-email-paul.gortmaker@windriver.com>
Date:	Wed, 5 Feb 2014 15:00:35 -0500
From:	Paul Gortmaker <paul.gortmaker@...driver.com>
To:	<stable@...r.kernel.org>, <linux-kernel@...r.kernel.org>
CC:	Mark Rutland <mark.rutland@....com>,
	<linux-arm-kernel@...ts.infradead.org>,
	"Jon Medhurst (Tixy)" <tixy@...aro.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Paul Gortmaker <paul.gortmaker@...driver.com>
Subject: [v2.6.34-stable 080/213] clockevents: Don't allow dummy broadcast timers

From: Mark Rutland <mark.rutland@....com>

                   -------------------
    This is a commit scheduled for the next v2.6.34 longterm release.
    http://git.kernel.org/?p=linux/kernel/git/paulg/longterm-queue-2.6.34.git
    If you see a problem with using this for longterm, please comment.
                   -------------------

commit a7dc19b8652c862d5b7c4d2339bd3c428bd29c4a upstream.

Currently tick_check_broadcast_device doesn't reject clock_event_devices
with CLOCK_EVT_FEAT_DUMMY, and may select them in preference to real
hardware if they have a higher rating value. In this situation, the
dummy timer is responsible for broadcasting to itself, and the core
clockevents code may attempt to call non-existent callbacks for
programming the dummy, eventually leading to a panic.

This patch makes tick_check_broadcast_device always reject dummy timers,
preventing this problem.

Signed-off-by: Mark Rutland <mark.rutland@....com>
Cc: linux-arm-kernel@...ts.infradead.org
Cc: Jon Medhurst (Tixy) <tixy@...aro.org>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Signed-off-by: Paul Gortmaker <paul.gortmaker@...driver.com>
---
 kernel/time/tick-broadcast.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/kernel/time/tick-broadcast.c b/kernel/time/tick-broadcast.c
index 521987f85874..ab16ee785b7f 100644
--- a/kernel/time/tick-broadcast.c
+++ b/kernel/time/tick-broadcast.c
@@ -67,7 +67,8 @@ static void tick_broadcast_start_periodic(struct clock_event_device *bc)
  */
 int tick_check_broadcast_device(struct clock_event_device *dev)
 {
-	if ((tick_broadcast_device.evtdev &&
+	if ((dev->features & CLOCK_EVT_FEAT_DUMMY) ||
+	    (tick_broadcast_device.evtdev &&
 	     tick_broadcast_device.evtdev->rating >= dev->rating) ||
 	     (dev->features & CLOCK_EVT_FEAT_C3STOP))
 		return 0;
-- 
1.8.5.2

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