linux-kernel - Re: [PATCH v3] clocksource: sun4i: Clear interrupts after stopping timer in probe function

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Message-ID: <20160825080409.GE7776@lukather>
Date:   Thu, 25 Aug 2016 10:04:09 +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,
        stable@...r.kernel.org
Subject: Re: [PATCH v3] clocksource: sun4i: Clear interrupts after stopping
 timer in probe function

On Thu, Aug 25, 2016 at 02:26:59PM +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.
> 
> Cc: stable@...r.kernel.org
> Signed-off-by: Chen-Yu Tsai <wens@...e.org>

Acked-by: Maxime Ripard <maxime.ripard@...e-electrons.com>

Thanks!
Maxime

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

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