linux-kernel - Re: [patch V3 28/35] PCI/MSI: Simplify pci_irq_get

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Date:   Mon, 31 Jan 2022 14:29:49 -0800
From:   Guenter Roeck <linux@...ck-us.net>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     LKML <linux-kernel@...r.kernel.org>, Nishanth Menon <nm@...com>,
        Mark Rutland <mark.rutland@....com>,
        Stuart Yoder <stuyoder@...il.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Will Deacon <will@...nel.org>, Ashok Raj <ashok.raj@...el.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Jassi Brar <jassisinghbrar@...il.com>,
        Sinan Kaya <okaya@...nel.org>,
        iommu@...ts.linux-foundation.org,
        Peter Ujfalusi <peter.ujfalusi@...il.com>,
        Bjorn Helgaas <helgaas@...nel.org>,
        linux-arm-kernel@...ts.infradead.org,
        Jason Gunthorpe <jgg@...dia.com>, linux-pci@...r.kernel.org,
        xen-devel@...ts.xenproject.org, Kevin Tian <kevin.tian@...el.com>,
        Arnd Bergmann <arnd@...db.de>,
        Robin Murphy <robin.murphy@....com>,
        Alex Williamson <alex.williamson@...hat.com>,
        Cedric Le Goater <clg@...d.org>,
        Santosh Shilimkar <ssantosh@...nel.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Megha Dey <megha.dey@...el.com>,
        Juergen Gross <jgross@...e.com>,
        Tero Kristo <kristo@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Vinod Koul <vkoul@...nel.org>, Marc Zygnier <maz@...nel.org>,
        dmaengine@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Subject: Re: [patch V3 28/35] PCI/MSI: Simplify pci_irq_get_affinity()

On Mon, Jan 31, 2022 at 10:16:41PM +0100, Thomas Gleixner wrote:
> Guenter,
> 
> On Mon, Jan 31 2022 at 07:21, Guenter Roeck wrote:
> > Sure. Please see http://server.roeck-us.net/qemu/x86/.
> > The logs are generated with with v5.16.4.
> 
> thanks for providing the data. It definitely helped me to leave the
> state of not seeing the wood for the trees. Fix below.
> 
> Thanks,
> 
>         tglx
> ---
> Subject: PCI/MSI: Remove bogus warning in pci_irq_get_affinity()
> From: Thomas Gleixner <tglx@...utronix.de>
> Date: Mon, 31 Jan 2022 22:02:46 +0100
> 
> The recent overhaul of pci_irq_get_affinity() introduced a regression when
> pci_irq_get_affinity() is called for an MSI-X interrupt which was not
> allocated with affinity descriptor information.
> 
> The original code just returned a NULL pointer in that case, but the rework
> added a WARN_ON() under the assumption that the corresponding WARN_ON() in
> the MSI case can be applied to MSI-X as well.
> 
> In fact the MSI warning in the original code does not make sense either
> because it's legitimate to invoke pci_irq_get_affinity() for a MSI
> interrupt which was not allocated with affinity descriptor information.
> 
> Remove it and just return NULL as the original code did.
> 
> Fixes: f48235900182 ("PCI/MSI: Simplify pci_irq_get_affinity()")
> Reported-by: Guenter Roeck <linux@...ck-us.net>
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>

Tested-by: Guenter Roeck <linux@...ck-us.net>

Guenter

> ---
>  drivers/pci/msi/msi.c |    3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> --- a/drivers/pci/msi/msi.c
> +++ b/drivers/pci/msi/msi.c
> @@ -1111,7 +1111,8 @@ const struct cpumask *pci_irq_get_affini
>  	if (!desc)
>  		return cpu_possible_mask;
>  
> -	if (WARN_ON_ONCE(!desc->affinity))
> +	/* MSI[X] interrupts can be allocated without affinity descriptor */
> +	if (!desc->affinity)
>  		return NULL;
>  
>  	/*