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Date:   Tue, 24 Jan 2017 08:55:01 +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, Seung-Woo Kim <sw0312.kim@...sung.com>,
        Joonyoung Shim <jy0922.shim@...sung.com>,
        linux-samsung-soc@...r.kernel.org, cw00.choi@...sung.com,
        daniel.lezcano@...aro.org, javier@....samsung.com,
        kgene@...nel.org, krzk@...nel.org,
        linux-arm-kernel@...ts.infradead.org,
        Thomas Gleixner <tglx@...utronix.de>
Subject: [PATCH 4.9 061/130] clocksource/exynos_mct: Clear interrupt when cpu is shut down

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

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

From: Joonyoung Shim <jy0922.shim@...sung.com>

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 <sw0312.kim@...sung.com>
Signed-off-by: Joonyoung Shim <jy0922.shim@...sung.com>
Cc: linux-samsung-soc@...r.kernel.org
Cc: cw00.choi@...sung.com
Cc: daniel.lezcano@...aro.org
Cc: javier@....samsung.com
Cc: kgene@...nel.org
Cc: krzk@...nel.org
Cc: linux-arm-kernel@...ts.infradead.org
Link: http://lkml.kernel.org/r/1484628876-22065-1-git-send-email-jy0922.shim@samsung.com
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

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

--- a/drivers/clocksource/exynos_mct.c
+++ b/drivers/clocksource/exynos_mct.c
@@ -495,6 +495,7 @@ static int exynos4_mct_dying_cpu(unsigne
 	if (mct_int_type == MCT_INT_SPI) {
 		if (evt->irq != -1)
 			disable_irq_nosync(evt->irq);
+		exynos4_mct_write(0x1, mevt->base + MCT_L_INT_CSTAT_OFFSET);
 	} else {
 		disable_percpu_irq(mct_irqs[MCT_L0_IRQ]);
 	}


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