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

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Date:	Tue, 26 Jul 2016 07:49:37 +0200
From:	Maxime Ripard <maxime.ripard@...e-electrons.com>
To:	Chen-Yu Tsai <wens@...e.org>
Cc:	Daniel Lezcano <daniel.lezcano@...aro.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] clocksource: sun4i: Clear interrupts after stopping
 timer in probe function

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.

Maxime

-- 
Maxime Ripard, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com

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