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Groups > linux.kernel > #1542660

[tip:smp/urgent] clocksource/dummy_timer: Move hotplug callback after the real timers

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Commit-ID:  9bf11ecce5a2758e5a097c2f3a13d08552d0d6f9
Gitweb:     http://git.kernel.org/tip/9bf11ecce5a2758e5a097c2f3a13d08552d0d6f9
Author:     Thomas Gleixner <tglx@linutronix.de>
AuthorDate: Thu, 15 Dec 2016 12:01:05 +0100
Committer:  Thomas Gleixner <tglx@linutronix.de>
CommitDate: Thu, 15 Dec 2016 12:09:20 +0100

clocksource/dummy_timer: Move hotplug callback after the real timers

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@free.fr>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Anna-Maria Gleixner <anna-maria@linutronix.de>
Cc: Richard Cochran <rcochran@linutronix.de>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Daniel Lezcano <daniel.lezcano@linaro.org>
Cc: Peter Zijlstra <peterz@infradead.org>,
Cc: Sebastian Frias <sf84@laposte.net>
Cc: Thibaud Cornic <thibaud_cornic@sigmadesigns.com>
Cc: Robin Murphy <robin.murphy@arm.com>
Link: http://lkml.kernel.org/r/1147ef90-7877-e4d2-bb2b-5c4fa8d3144b@free.fr
---
 include/linux/cpuhotplug.h | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/include/linux/cpuhotplug.h b/include/linux/cpuhotplug.h
index 22acee7..2ab7bf5 100644
--- a/include/linux/cpuhotplug.h
+++ b/include/linux/cpuhotplug.h
@@ -101,7 +101,6 @@ 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,
@@ -115,6 +114,8 @@ 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,

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Re: Linux crashes when trying to online secondary core Mason <slash.tmp@free.fr> - 2016-12-15 11:40 +0100
  [tip:timers/urgent] tick/broadcast: Prevent NULL pointer  dereference tip-bot for Thomas Gleixner <tipbot@zytor.com> - 2016-12-15 12:40 +0100
  [tip:smp/urgent] clocksource/dummy_timer: Move hotplug callback  after the real timers tip-bot for Thomas Gleixner <tipbot@zytor.com> - 2016-12-15 12:50 +0100
  Re: Linux crashes when trying to online secondary core Mark Rutland <mark.rutland@arm.com> - 2016-12-15 13:10 +0100

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