From: Marc Zyngier <maz@kernel.org>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: "Herrenschmidt, Benjamin" <benh@amazon.com>,
"Saidi, Ali" <alisaidi@amazon.com>,
jason@lakedaemon.net, linux-kernel@vger.kernel.org,
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
Date: Wed, 03 Jun 2020 13:44:58 +0100 [thread overview]
Message-ID: <d08bd61ffffe59091f6542b4f75292d1@kernel.org> (raw)
In-Reply-To: <87y2p5fatl.fsf@nanos.tec.linutronix.de>
On 2020-06-02 21:54, Thomas Gleixner wrote:
> "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);
Grump. Nice catch. In hindsight, this is obvious, as managed interrupts
may have been allocated to target CPUs that have been hot-plugged off.
>> 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.
Indeed. I completely missed the above. Back to square one.
Thanks,
M.
--
Jazz is not dead. It just smells funny...
next prev parent reply other threads:[~2020-06-03 12:45 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-29 1:55 [PATCH] irqchip/gic-v3-its: Don't try to move a disabled irq Ali Saidi
2020-05-29 4:07 ` Zenghui Yu
2020-05-29 8:32 ` Marc Zyngier
2020-05-29 12:36 ` Saidi, Ali
2020-05-30 16:49 ` Marc Zyngier
2020-05-31 11:09 ` Marc Zyngier
2020-06-01 0:10 ` Saidi, Ali
2020-06-01 2:40 ` Herrenschmidt, Benjamin
2020-06-02 20:54 ` Thomas Gleixner
2020-06-03 12:44 ` Marc Zyngier [this message]
2020-05-31 2:53 ` kbuild test robot
2020-07-17 21:34 ` [tip: irq/urgent] genirq/affinity: Handle affinity setting on inactive interrupts correctly tip-bot2 for Thomas Gleixner
2020-06-02 18:47 [PATCH] irqchip/gic-v3-its: Don't try to move a disabled irq Saidi, Ali
2020-06-03 15:16 ` Marc Zyngier
2020-06-03 22:14 ` Herrenschmidt, Benjamin
2020-06-08 13:48 ` Thomas Gleixner
2020-06-08 21:59 ` Benjamin Herrenschmidt
2020-06-08 23:36 ` Thomas Gleixner
2020-06-11 17:44 Saidi, Ali
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