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

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Date:   Mon, 2 Nov 2020 17:32:32 +0000
From:   John Garry <john.garry@...wei.com>
To:     Thomas Gleixner <tglx@...utronix.de>, <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()

On 28/10/2020 18:22, Thomas Gleixner wrote:
> On Wed, Oct 28 2020 at 20:33, John Garry wrote:

Hi Thomas,

>>   
>> +int irq_update_affinity_desc(unsigned int irq,
>> +			     struct irq_affinity_desc *affinity)
>> +{
>> +	unsigned long flags;
>> +	struct irq_desc *desc = irq_get_desc_lock(irq, &flags, 0);
>> +
>> +	if (!desc)
>> +		return -EINVAL;
> Just looking at it some more. This needs a check whether the interrupt
> is actually shut down. Otherwise the update will corrupt
> state. Something like this:
> 
>          if (irqd_is_started(&desc->irq_data))
>          	return -EBUSY;
> 
> But all of this can't work on x86 due to the way how vector allocation
> works. Let me think about that.
> 

Is the problem that we reserve per-cpu managed interrupt space when 
allocated irq vectors on x86, and so later changing managed vs 
non-managed setting for irqs messes up this accounting somehow?

Cheers,
John