linux-kernel - Re: [PATCH] clocksource: sun4i: Clear interrupts after stopping timer in probe function

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Date:	Tue, 26 Jul 2016 14:42:00 +0800
From:	Chen-Yu Tsai <wens@...e.org>
To:	Maxime Ripard <maxime.ripard@...e-electrons.com>
Cc:	Chen-Yu Tsai <wens@...e.org>,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] clocksource: sun4i: Clear interrupts after stopping timer
 in probe function

On Tue, Jul 26, 2016 at 1:49 PM, Maxime Ripard
<maxime.ripard@...e-electrons.com> wrote:
> On Tue, Jul 26, 2016 at 11:01:59AM +0800, Chen-Yu Tsai wrote:
>> The bootloader (U-boot) sometimes uses this timer for various delays.
>> It uses it as a ongoing counter, and does comparisons on the current
>> counter value. The timer counter is never stopped.
>>
>> In some cases when the user interacts with the bootloader, or lets
>> it idle for some time before loading Linux, the timer may expire,
>> and an interrupt will be pending. This results in an unexpected
>> interrupt when the timer interrupt is enabled by the kernel, at
>> which point the event_handler isn't set yet. This results in a NULL
>> pointer dereference exception, panic, and no way to reboot.
>>
>> Clear any pending interrupts after we stop the timer in the probe
>> function to avoid this.
>>
>> Signed-off-by: Chen-Yu Tsai <wens@...e.org>
>
> Awesome, thanks!
>
> You should put stable in Cc though for this kind of patches.

AFAIK some maintainers prefer to add it themselves. Not sure about
clocksource so I left it out.

ChenYu