linux-kernel - Re: [PATCH v2 1/3] genirq/affinity: Add irq_update_affinity

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Date:   Wed, 18 Nov 2020 21:38:20 +0100
From:   Thomas Gleixner <tglx@...utronix.de>
To:     John Garry <john.garry@...wei.com>, gregkh@...uxfoundation.org,
        rafael@...nel.org, martin.petersen@...cle.com, jejb@...ux.ibm.com
Cc:     linuxarm@...wei.com, linux-scsi@...r.kernel.org,
        linux-kernel@...r.kernel.org, maz@...nel.org
Subject: Re: [PATCH v2 1/3] genirq/affinity: Add irq_update_affinity_desc()

John,

On Wed, Nov 18 2020 at 11:34, John Garry wrote:
>> +/**
>> + * irq_update_affinity_desc - Update affinity management for an interrupt
>> + * @irq:	The interrupt number to update
>> + * @affinity:	Pointer to the affinity descriptor
>> + *
>> + * This interface can be used to configure the affinity management of
>> + * interrupts which have been allocated already.
>> + */
>> +int irq_update_affinity_desc(unsigned int irq,
>> +			     struct irq_affinity_desc *affinity)
>
> Just a note on the return value, in the only current callsite - 
> platform_get_irqs_affinity() - we don't check the return value and 
> propagate the error. This is because we don't want to fail the interrupt 
> init just because of problems updating the affinity mask. So I could 
> print a message to inform the user of error (at the callsite).

Well, not sure about that. During init on a platform which does not have
the issues with reservation mode there failure cases are:

 1) Interrupt does not exist. Definitely a full fail

 2) Interrupt is already started up. Not a good idea on init() and
    a clear fail.

 3) Interrupt has already been switched to managed. Double init is not
    really a good sign either.

>> +	/* Requires the interrupt to be shut down */
>> +	if (irqd_is_started(&desc->irq_data))
>
> We're missing the unlock here, right?

Duh yes.

>> +		return -EBUSY;
>> +
>> +	/* Interrupts which are already managed cannot be modified */
>> +	if (irqd_is_managed(&desc->irq_data))
>
> And here, and I figure that this should be irqd_affinity_is_managed()

More duh :)

I assume you send a fixed variant of this.

Thanks,

        tglx