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

[Keith Busch]

On Tue, Oct 30, 2018 at 08:36:35AM -0600, Jens Axboe wrote:
> 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.

'nvecs' is what irq_calc_affinity_vectors() returns, which is the min
of either the requested max or the sum of the set, and the sum of the set
isn't guaranteed to be the smaller value.