netdev - Re: [PATCH net-next V3 1/2] net: Utility function to get affinity

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Message-Id: <20140306.153835.2248996436618700806.davem@davemloft.net>
Date:	Thu, 06 Mar 2014 15:38:35 -0500 (EST)
From:	David Miller <davem@...emloft.net>
To:	amirv@...lanox.com
Cc:	netdev@...r.kernel.org, yevgenyp@...lanox.com,
	ogerlitz@...lanox.com, prarit@...hat.com, gvaradar@...co.com
Subject: Re: [PATCH net-next V3 1/2] net: Utility function to get
 affinity_hint by policy

From: Amir Vadai <amirv@...lanox.com>
Date: Thu,  6 Mar 2014 19:18:51 +0200

> +	rxq %= num_online_cpus();
> +
> +	p_numa_cores_mask = cpumask_of_node(numa_node);
> +	if (!p_numa_cores_mask)
> +		p_numa_cores_mask = cpu_online_mask;
> +
> +	for_each_cpu(affinity_cpu, p_numa_cores_mask) {
> +		if (--rxq < 0)
> +			goto out;
> +	}
> +
> +	if (!zalloc_cpumask_var(&non_numa_cores_mask, GFP_KERNEL)) {
> +		ret = -ENOMEM;
> +		goto err;
> +	}
> +
> +	cpumask_xor(non_numa_cores_mask, cpu_online_mask, p_numa_cores_mask);
> +
> +	for_each_cpu(affinity_cpu, non_numa_cores_mask) {
> +		if (--rxq < 0)
> +			goto out;
> +	}
> +
> +	ret = -EINVAL;
> +	goto err;

The NUMA core mask and the non-NUMA core mask must together provide
at least num_online_cpus() bits.

Said another way, since rxq is limited to num_online_cpus() it should
never exceed local + non-local cores.

Therefore this -EINVAL path seems like it should not be possible, and
therefore perhaps a WARN_ON() or similar would be appropriate.
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