netdev - Re: [PATCH V5 net-next] net: mana: Assigning IRQ affinity on HT cores

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Date: Tue, 12 Dec 2023 08:34:02 -0800
From: Yury Norov <yury.norov@...il.com>
To: Souradeep Chakrabarti <schakrabarti@...ux.microsoft.com>
Cc: kys@...rosoft.com, haiyangz@...rosoft.com, wei.liu@...nel.org,
	decui@...rosoft.com, davem@...emloft.net, edumazet@...gle.com,
	kuba@...nel.org, pabeni@...hat.com, longli@...rosoft.com,
	leon@...nel.org, cai.huoqing@...ux.dev, ssengar@...ux.microsoft.com,
	vkuznets@...hat.com, tglx@...utronix.de,
	linux-hyperv@...r.kernel.org, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-rdma@...r.kernel.org,
	schakrabarti@...rosoft.com, paulros@...rosoft.com
Subject: Re: [PATCH V5 net-next] net: mana: Assigning IRQ affinity on HT cores

> > > > > +	rcu_read_lock();
> > > > > +	for_each_numa_hop_mask(next, next_node) {
> > > > > +		cpumask_andnot(curr, next, prev);
> > > > > +		for (w = cpumask_weight(curr), cnt = 0; cnt < w; ) {
> > > > > +			cpumask_copy(cpus, curr);
> > > > > +			for_each_cpu(cpu, cpus) {
> > > > > +				irq_set_affinity_and_hint(irqs[i], topology_sibling_cpumask(cpu));
> > > > > +				if (++i == nvec)
> > > > > +					goto done;
> > > > 
> > > > Think what if you're passed with irq_setup(NULL, 0, 0).
> > > > That's why I suggested to place this check at the beginning.
> > > > 
> > > irq_setup() is a helper function for mana_gd_setup_irqs(), which already takes
> > > care of no NULL pointer for irqs, and 0 number of interrupts can not be passed.
> > > 
> > > nvec = pci_alloc_irq_vectors(pdev, 2, max_irqs, PCI_IRQ_MSIX);
> > > if (nvec < 0)
> > > 	return nvec;
> > 
> > I know that. But still it's a bug. The common convention is that if a
> > 0-length array is passed to a function, it should not dereference the
> > pointer.
> > 
> I will add one if check in the begining of irq_setup() to verify the pointer
> and the nvec number.

Yes you can, but what for? This is an error anyways, and you don't
care about early return. So instead of adding and bearing extra logic,
I'd just swap 2 lines of existing code.