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

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Message-ID: <87sg9en79m.fsf@nanos.tec.linutronix.de>
Date:   Thu, 12 Nov 2020 12:28:53 +0100
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Bjorn Helgaas <helgaas@...nel.org>,
        Martin Kaiser <martin@...ser.cx>
Cc:     Ley Foon Tan <ley.foon.tan@...el.com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        rfi@...ts.rocketboards.org, linux-pci@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Nicolas Saenz Julienne <nsaenzjulienne@...e.de>,
        Jingoo Han <jingoohan1@...il.com>,
        Gustavo Pimentel <gustavo.pimentel@...opsys.com>,
        Toan Le <toan@...amperecomputing.com>,
        Florian Fainelli <f.fainelli@...il.com>
Subject: Re: [PATCH] PCI: altera-msi: Remove irq handler and data in one go

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