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Date:   Tue, 24 Jan 2017 08:55:35 +0100
From:   Greg Kroah-Hartman <>
Cc:     Greg Kroah-Hartman <>,, Seung-Woo Kim <>,
        Joonyoung Shim <>,,,,,,,,
        Thomas Gleixner <>
Subject: [PATCH 4.4 25/42] clocksource/exynos_mct: Clear interrupt when cpu is shut down

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


From: Joonyoung Shim <>

commit bc7c36eedb0c7004aa06c2afc3c5385adada8fa3 upstream.

When a CPU goes offline a potentially pending timer interrupt is not
cleared. When the CPU comes online again then the pending interrupt is
delivered before the per cpu clockevent device is initialized. As a
consequence the tick interrupt handler dereferences a NULL pointer.

[   51.251378] Unable to handle kernel NULL pointer dereference at virtual address 00000040
[   51.289348] task: ee942d00 task.stack: ee960000
[   51.293861] PC is at tick_periodic+0x38/0xb0
[   51.298102] LR is at tick_handle_periodic+0x1c/0x90

Clear the pending interrupt in the cpu dying path.

Fixes: 56a94f13919c ("clocksource: exynos_mct: Avoid blocking calls in the cpu hotplug notifier")
Reported-by: Seung-Woo Kim <>
Signed-off-by: Joonyoung Shim <>
Signed-off-by: Thomas Gleixner <>
Signed-off-by: Greg Kroah-Hartman <>

 drivers/clocksource/exynos_mct.c |    1 +
 1 file changed, 1 insertion(+)

--- a/drivers/clocksource/exynos_mct.c
+++ b/drivers/clocksource/exynos_mct.c
@@ -482,6 +482,7 @@ static void exynos4_local_timer_stop(str
 	if (mct_int_type == MCT_INT_SPI) {
 		if (evt->irq != -1)
+		exynos4_mct_write(0x1, mevt->base + MCT_L_INT_CSTAT_OFFSET);
 	} else {

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