linux-kernel - Re: [RFC v4 22/22] timekeeping: inform clockevents about freq adjustments

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Message-ID: <alpine.DEB.2.20.1608251714230.5714@nanos>
Date:   Thu, 25 Aug 2016 17:25:53 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Nicolai Stange <nicstange@...il.com>
cc:     John Stultz <john.stultz@...aro.org>, linux-kernel@...r.kernel.org
Subject: Re: [RFC v4 22/22] timekeeping: inform clockevents about freq
 adjustments

On Tue, 23 Aug 2016, Nicolai Stange wrote:
> +	raw_spin_lock_irqsave(&clockevents_lock, flags);
> +	list_for_each_entry(dev, &clockevent_devices, list) {
> +		if (!(dev->features & CLOCK_EVT_FEAT_ONESHOT))
> +			continue;
> +
> +		mult_raw = dev->mult;
> +		if (mult_raw != last_mult_raw) {
> +			last_mult_raw = mult_raw;
> +			last_mult_adjusted =
> +				__clockevents_calc_adjust_freq(mult_raw,
> +							mult_cs_mono,
> +							mult_cs_raw);

What makes sure that the resulting shift/mult pair is still valid after this
adjustment? The non adjusted mult/shift pair might be right at the border of
potential overflows and the adjustment might just put it over the edge....
We need at least sanity checks here.

Thanks,

	tglx