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From:   Thomas Gleixner <tglx@linutronix.de>
To:     "Herrenschmidt\, Benjamin" <benh@amazon.com>,
        "maz\@kernel.org" <maz@kernel.org>,
        "Saidi\, Ali" <alisaidi@amazon.com>
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        <linux-arm-kernel@lists.infradead.org>,
        "Woodhouse\, David" <dwmw@amazon.co.uk>,
        "Zilberman\, Zeev" <zeev@amazon.com>,
        "Machulsky\, Zorik" <zorik@amazon.com>
Subject: Re: [PATCH] irqchip/gic-v3-its: Don't try to move a disabled irq
In-Reply-To: <37e55e71faf76dc3db76d89c20c1bdfff942e380.camel@amazon.com>
References: <20200529015501.15771-1-alisaidi@amazon.com> <8c3be990888ecfb7cca9503853dc4aac@kernel.org> <2C4F431F-8140-4C82-B4BD-E51DE618FC08@amazon.com> <20200530174929.7bf6d5d7@why> <eed907d48de84c96e3ceb27c1ed6f622@kernel.org> <37e55e71faf76dc3db76d89c20c1bdfff942e380.camel@amazon.com>
Date:   Tue, 02 Jun 2020 22:54:14 +0200
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"Herrenschmidt, Benjamin" <benh@amazon.com> writes:
> On Sun, 2020-05-31 at 12:09 +0100, Marc Zyngier wrote:
>> > The semantic of activate/deactivate (which maps to started/shutdown
>> > in the IRQ code) is that the HW resources for a given interrupt are
>> > only committed when the interrupt is activated. Trying to perform
>> > actions involving the HW on an interrupt that isn't active cannot be
>> > guaranteed to take effect.
>> > 
>> > I'd rather address it in the core code, by preventing set_affinity (and
>> > potentially others) to take place when the interrupt is not in the
>> > STARTED state. Userspace would get an error, which is perfectly
>> > legitimate, and which it already has to deal with it for plenty of
>> > other
>> > reasons.
>
> So I finally found time to dig a bit in there :) Code has changed a bit
> since last I looked. But I have memories of the startup code messing
> around with the affinity, and here it is. In irq_startup() :
>
>
> 		switch (__irq_startup_managed(desc, aff, force)) {
> 		case IRQ_STARTUP_NORMAL:
> 			ret = __irq_startup(desc);
> 			irq_setup_affinity(desc);
> 			break;
> 		case IRQ_STARTUP_MANAGED:
> 			irq_do_set_affinity(d, aff, false);
> 			ret = __irq_startup(desc);
> 			break;
> 		case IRQ_STARTUP_ABORT:
> 			irqd_set_managed_shutdown(d);
> 			return 0;
>
> So we have two cases here. Normal and managed.
>
> In the managed case, we set the affinity before startup. I feel like your
> patch might break that or am I missing something ?

It will break stuff because the affinity is not stored in case that the
interrupt is not started.

I think we can fix this in the core code but that needs more thought.
__irq_can_set_affinity() is definitely the wrong place.

Thanks,

        tglx