Re: [PATCH] PCI: altera-msi: Remove irq handler and data in one go

From: Thomas Gleixner <tglx@linutronix.de>
To: Bjorn Helgaas <helgaas@kernel.org>, Martin Kaiser <martin@kaiser.cx>
Cc: Ley Foon Tan <ley.foon.tan@intel.com>,
	Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>,
	Bjorn Helgaas <bhelgaas@google.com>,
	rfi@lists.rocketboards.org, linux-pci@vger.kernel.org,
	linux-kernel@vger.kernel.org,
	Nicolas Saenz Julienne <nsaenzjulienne@suse.de>,
	Jingoo Han <jingoohan1@gmail.com>,
	Gustavo Pimentel <gustavo.pimentel@synopsys.com>,
	Toan Le <toan@os.amperecomputing.com>,
	Florian Fainelli <f.fainelli@gmail.com>
Subject: Re: [PATCH] PCI: altera-msi: Remove irq handler and data in one go
Date: Thu, 12 Nov 2020 12:28:53 +0100	[thread overview]
Message-ID: <87sg9en79m.fsf@nanos.tec.linutronix.de> (raw)
In-Reply-To: <20201111221639.GA973514@bjorn-Precision-5520>

On Wed, Nov 11 2020 at 16:16, Bjorn Helgaas wrote:
> On Wed, Nov 11, 2020 at 10:43:55PM +0100, Martin Kaiser wrote:
>> This function uses the error status from irq_set_handler_data().
>> irq_set_chained_handler_and_data() returns no such error status. Is it
>> ok to drop the error handling?
>
> I'm not an IRQ expert, but I'd say it's OK to drop it.  Of the 40 or
> so callers, the only other caller that looks at the error status is
> ingenic_intc_of_init().

Don't know why irq_set_chained_handler_and_data() does not return an
error, but the call site must really do something stupid if it fails to
hand in the proper interrupt number.

> Thomas, it looks like irq_domain_set_info() and msi_domain_ops_init()
> set the handler itself before setting the handler data:
>
>   irq_domain_set_info
>     irq_set_chip_and_handler_name(virq, chip, handler, ...)
>     irq_set_handler_data(virq, handler_data)
>
>   msi_domain_ops_init
>     __irq_set_handler(virq, info->handler, ...)
>     if (info->handler_data)
>       irq_set_handler_data(virq, info->handler_data)
>
> That looks at least superficially similar to the race you fixed with
> 2cf5a03cb29d ("PCI/keystone: Fix race in installing chained IRQ
> handler").
>
> Should irq_domain_set_info() and msi_domain_ops_init() swap the order,
> too?

In theory yes. Practically it should not matter because that happens
during the allocation way before the interrupt can actually fire.  I'll
have a deeper look nevertheless.

Thanks,

        tglx