4.9-stable review patch. If anyone has any objections, please let me know. ------------------ From: Joonyoung Shim <jy0922.shim@xxxxxxxxxxx> 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@xxxxxxxxxxx> Signed-off-by: Joonyoung Shim <jy0922.shim@xxxxxxxxxxx> Cc: linux-samsung-soc@xxxxxxxxxxxxxxx Cc: cw00.choi@xxxxxxxxxxx Cc: daniel.lezcano@xxxxxxxxxx Cc: javier@xxxxxxxxxxxxxxx Cc: kgene@xxxxxxxxxx Cc: krzk@xxxxxxxxxx Cc: linux-arm-kernel@xxxxxxxxxxxxxxxxxxx Link: http://lkml.kernel.org/r/1484628876-22065-1-git-send-email-jy0922.shim@xxxxxxxxxxx Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- 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]); } -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html