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

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Date:	Tue, 26 Jul 2016 11:07:37 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Chen-Yu Tsai <wens@...e.org>
cc:	Maxime Ripard <maxime.ripard@...e-electrons.com>,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
	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, 26 Jul 2016, Chen-Yu Tsai wrote:
> 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.

At least you should tell the maintainer, that you consider this to be stable
material. It's not an obvious stable candidate.

Thanks,

	tglx