Re: [PATCH 11/14] irq: add support for allocating (and affinitizing) sets of IRQs

[Jens Axboe]

On 10/30/18 8:26 AM, Keith Busch wrote:
> On Mon, Oct 29, 2018 at 10:37:35AM -0600, Jens Axboe wrote:
>> diff --git a/kernel/irq/affinity.c b/kernel/irq/affinity.c
>> index f4f29b9d90ee..2046a0f0f0f1 100644
>> --- a/kernel/irq/affinity.c
>> +++ b/kernel/irq/affinity.c
>> @@ -180,6 +180,7 @@ irq_create_affinity_masks(int nvecs, const struct irq_affinity *affd)
>>  	int curvec, usedvecs;
>>  	cpumask_var_t nmsk, npresmsk, *node_to_cpumask;
>>  	struct cpumask *masks = NULL;
>> +	int i, nr_sets;
>>  
>>  	/*
>>  	 * If there aren't any vectors left after applying the pre/post
>> @@ -210,10 +211,23 @@ irq_create_affinity_masks(int nvecs, const struct irq_affinity *affd)
>>  	get_online_cpus();
>>  	build_node_to_cpumask(node_to_cpumask);
>>  
>> -	/* Spread on present CPUs starting from affd->pre_vectors */
>> -	usedvecs = irq_build_affinity_masks(affd, curvec, affvecs,
>> -					    node_to_cpumask, cpu_present_mask,
>> -					    nmsk, masks);
>> +	/*
>> +	 * Spread on present CPUs starting from affd->pre_vectors. If we
>> +	 * have multiple sets, build each sets affinity mask separately.
>> +	 */
>> +	nr_sets = affd->nr_sets;
>> +	if (!nr_sets)
>> +		nr_sets = 1;
>> +
>> +	for (i = 0, usedvecs = 0; i < nr_sets; i++) {
>> +		int this_vecs = affd->sets ? affd->sets[i] : affvecs;
>> +		int nr;
>> +
>> +		nr = irq_build_affinity_masks(affd, curvec, this_vecs,
>> +					      node_to_cpumask, cpu_present_mask,
>> +					      nmsk, masks + usedvecs);
>> +		usedvecs += nr;
>> +	}
> 
> 
> While the code below returns the appropriate number of possible vectors
> when a set requested too many, the above code is still using the value
> from the set, which may exceed 'nvecs' used to kcalloc 'masks', so
> 'masks + usedvecs' may go out of bounds.

How so? nvecs must the max number of vecs, the sum of the sets can't
exceed that value.

-- 
Jens Axboe