linux-kernel - [PATCH 4.9 205/206] clocksource/dummy_timer: Move hotplug callback after the real timers

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Date:   Tue, 10 Jan 2017 14:38:08 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
        Mark Rutland <mark.rutland@....com>,
        Anna-Maria Gleixner <anna-maria@...utronix.de>,
        Richard Cochran <rcochran@...utronix.de>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Sebastian Frias <sf84@...oste.net>,
        Thibaud Cornic <thibaud_cornic@...madesigns.com>,
        Robin Murphy <robin.murphy@....com>,
        Peter Zijlstra <peterz@...radead.org>
Subject: [PATCH 4.9 205/206] clocksource/dummy_timer: Move hotplug callback after the real timers

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

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

From: Thomas Gleixner <tglx@...utronix.de>

commit 9bf11ecce5a2758e5a097c2f3a13d08552d0d6f9 upstream.

When the dummy timer callback is invoked before the real timer callbacks,
then it tries to install that timer for the starting CPU. If the platform
does not have a broadcast timer installed the installation fails with a
kernel crash. The crash happens due to a unconditional deference of the non
available broadcast device. This needs to be fixed in the timer core code.

But even when this is fixed in the core code then installing the dummy
timer before the real timers is a pointless exercise.

Move it to the end of the callback list.

Fixes: 00c1d17aab51 ("clocksource/dummy_timer: Convert to hotplug state machine")
Reported-and-tested-by: Mason <slash.tmp@...e.fr>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Cc: Mark Rutland <mark.rutland@....com>
Cc: Anna-Maria Gleixner <anna-maria@...utronix.de>
Cc: Richard Cochran <rcochran@...utronix.de>
Cc: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc: Daniel Lezcano <daniel.lezcano@...aro.org>
Cc: Peter Zijlstra <peterz@...radead.org>,
Cc: Sebastian Frias <sf84@...oste.net>
Cc: Thibaud Cornic <thibaud_cornic@...madesigns.com>
Cc: Robin Murphy <robin.murphy@....com>
Link: http://lkml.kernel.org/r/1147ef90-7877-e4d2-bb2b-5c4fa8d3144b@free.fr
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 include/linux/cpuhotplug.h |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/include/linux/cpuhotplug.h
+++ b/include/linux/cpuhotplug.h
@@ -80,7 +80,6 @@ enum cpuhp_state {
 	CPUHP_AP_ARM_L2X0_STARTING,
 	CPUHP_AP_ARM_ARCH_TIMER_STARTING,
 	CPUHP_AP_ARM_GLOBAL_TIMER_STARTING,
-	CPUHP_AP_DUMMY_TIMER_STARTING,
 	CPUHP_AP_JCORE_TIMER_STARTING,
 	CPUHP_AP_EXYNOS4_MCT_TIMER_STARTING,
 	CPUHP_AP_ARM_TWD_STARTING,
@@ -94,6 +93,8 @@ enum cpuhp_state {
 	CPUHP_AP_KVM_ARM_VGIC_INIT_STARTING,
 	CPUHP_AP_KVM_ARM_VGIC_STARTING,
 	CPUHP_AP_KVM_ARM_TIMER_STARTING,
+	/* Must be the last timer callback */
+	CPUHP_AP_DUMMY_TIMER_STARTING,
 	CPUHP_AP_ARM_XEN_STARTING,
 	CPUHP_AP_ARM_CORESIGHT_STARTING,
 	CPUHP_AP_ARM_CORESIGHT4_STARTING,