linux-kernel - Re: [patch v6 3/7] genirq/affinity: Add new callback for (re)calculating interrupt sets

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Date:   Fri, 18 Jun 2021 21:19:12 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Bjorn Helgaas <helgaas@...nel.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Ming Lei <ming.lei@...hat.com>, Christoph Hellwig <hch@....de>,
        Jens Axboe <axboe@...nel.dk>, linux-block@...r.kernel.org,
        Sagi Grimberg <sagi@...mberg.me>,
        linux-nvme@...ts.infradead.org, linux-pci@...r.kernel.org,
        Keith Busch <keith.busch@...el.com>,
        Marc Zyngier <marc.zyngier@....com>,
        Sumit Saxena <sumit.saxena@...adcom.com>,
        Kashyap Desai <kashyap.desai@...adcom.com>,
        Shivasharan Srikanteshwara 
        <shivasharan.srikanteshwara@...adcom.com>
Subject: Re: [patch v6 3/7] genirq/affinity: Add new callback for (re)calculating interrupt sets

On Tue, Jun 15 2021 at 14:57, Bjorn Helgaas wrote:
>
>> @@ -1196,6 +1196,13 @@ int pci_alloc_irq_vectors_affinity(struc
>>  	/* use legacy irq if allowed */
>>  	if (flags & PCI_IRQ_LEGACY) {
>>  		if (min_vecs == 1 && dev->irq) {
>> +			/*
>> +			 * Invoke the affinity spreading logic to ensure that
>> +			 * the device driver can adjust queue configuration
>> +			 * for the single interrupt case.
>> +			 */
>> +			if (affd)
>> +				irq_create_affinity_masks(1, affd);
>
> This looks like a leak because irq_create_affinity_masks() returns a
> pointer to kcalloc()ed space, but we throw away the pointer.
>
> Or is there something very subtle going on here, like this special
> case doesn't allocate anything?  I do see the "Nothing to assign?"
> case that returns NULL with no alloc, but it's not completely trivial
> to verify that we take that case here.

Yes, it's subtle and it's subtle crap. Sorry that I did not catch that.

Thanks,

        tglx