Re: [PATCH] PCI/MSI: Only disable affinity settings if pre and post vector count is equal to max_vecs and not min_vecs

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Your summary is "Only disable affinity settings if pre and post vector
count is equal to max_vecs and not min_vecs", but the patch doesn't
mention max_vecs anywhere.  There must be a clearer way to word this.

On Mon, Apr 17, 2017 at 06:19:25PM -0700, Himanshu Madhani wrote:
> min_vecs is the minimum amount of vectors needed to operate in MSI-X mode
> which may just include the vectors that don't need affinity.
> 
> Disabling affinity settings causes the qla2xxx driver scsi_add_host
> to fail when blk_mq is enabled as the blk_mq_pci_map_queues expects
> affinity masks on each vector.
> 
> Fixes: dfef358bd1be ("PCI/MSI: Don't apply affinity if there aren't enough vectors left")
> Signed-off-by: Michael Hernandez <michael.hernandez@xxxxxxxxxx>
> Signed-off-by: Himanshu Madhani <himanshu.madhani@xxxxxxxxxx>
> Cc: <stable@xxxxxxxxxxxxxxx> # 4.10
> ---
> v4 --> v5
> o Fixed Zero day kernel build failure.
> 
> v3 --> v4
> o Moved pre/post reserved vector range checks to affinity.c as per
>   comments from Bjorn Helgaas.
> 
> v2 --> v3
> o fixed code as per review comments.
> 
> v1 --> v2
> o Moved the check from pci_alloc_irq_vectors_affinity() to
>   __pci_enable_{msi|msix}_range()
> 
> 
>  drivers/pci/msi.c         | 14 ++------------
>  include/linux/interrupt.h |  4 ++--
>  kernel/irq/affinity.c     | 12 +++++++++++-
>  3 files changed, 15 insertions(+), 15 deletions(-)
> 
> diff --git a/drivers/pci/msi.c b/drivers/pci/msi.c
> index d571bc330686..8adf22f41cf9 100644
> --- a/drivers/pci/msi.c
> +++ b/drivers/pci/msi.c
> @@ -1072,7 +1072,7 @@ static int __pci_enable_msi_range(struct pci_dev *dev, int minvec, int maxvec,
>  
>  	for (;;) {
>  		if (affd) {
> -			nvec = irq_calc_affinity_vectors(nvec, affd);
> +			nvec = irq_calc_affinity_vectors(minvec, nvec, affd);
>  			if (nvec < minvec)
>  				return -ENOSPC;
>  		}
> @@ -1111,7 +1111,7 @@ static int __pci_enable_msix_range(struct pci_dev *dev,
>  
>  	for (;;) {
>  		if (affd) {
> -			nvec = irq_calc_affinity_vectors(nvec, affd);
> +			nvec = irq_calc_affinity_vectors(minvec, nvec, affd);
>  			if (nvec < minvec)
>  				return -ENOSPC;
>  		}
> @@ -1179,16 +1179,6 @@ int pci_alloc_irq_vectors_affinity(struct pci_dev *dev, unsigned int min_vecs,
>  	if (flags & PCI_IRQ_AFFINITY) {
>  		if (!affd)
>  			affd = &msi_default_affd;
> -
> -		if (affd->pre_vectors + affd->post_vectors > min_vecs)
> -			return -EINVAL;
> -
> -		/*
> -		 * If there aren't any vectors left after applying the pre/post
> -		 * vectors don't bother with assigning affinity.
> -		 */
> -		if (affd->pre_vectors + affd->post_vectors == min_vecs)
> -			affd = NULL;
>  	} else {
>  		if (WARN_ON(affd))
>  			affd = NULL;
> diff --git a/include/linux/interrupt.h b/include/linux/interrupt.h
> index 53144e78a369..63b246dd8258 100644
> --- a/include/linux/interrupt.h
> +++ b/include/linux/interrupt.h
> @@ -291,7 +291,7 @@ extern int
>  irq_set_affinity_notifier(unsigned int irq, struct irq_affinity_notify *notify);
>  
>  struct cpumask *irq_create_affinity_masks(int nvec, const struct irq_affinity *affd);
> -int irq_calc_affinity_vectors(int maxvec, const struct irq_affinity *affd);
> +int irq_calc_affinity_vectors(int minvec, int maxvec, const struct irq_affinity *affd);
>  
>  #else /* CONFIG_SMP */
>  
> @@ -331,7 +331,7 @@ irq_create_affinity_masks(int nvec, const struct irq_affinity *affd)
>  }
>  
>  static inline int
> -irq_calc_affinity_vectors(int maxvec, const struct irq_affinity *affd)
> +irq_calc_affinity_vectors(int minvec, int maxvec, const struct irq_affinity *affd)
>  {
>  	return maxvec;
>  }
> diff --git a/kernel/irq/affinity.c b/kernel/irq/affinity.c
> index d052947fe785..59645fa66385 100644
> --- a/kernel/irq/affinity.c
> +++ b/kernel/irq/affinity.c
> @@ -69,6 +69,13 @@ irq_create_affinity_masks(int nvecs, const struct irq_affinity *affd)
>  	if (!zalloc_cpumask_var(&nmsk, GFP_KERNEL))
>  		return NULL;
>  
> +	/*
> +	 * If there aren't any vectors left after applying the pre/post
> +	 * vectors don't bother with assigning affinity.
> +	 */
> +	if (!affv)
> +		return NULL;

This looks like it might require cleanup, e.g., branching to "out".

But the test of "affv" doesn't depend on the zalloc_cpu_mask_var(), so
you could just move this test above the call to zalloc_cpu_mask_var(),
and then you wouldn't need any cleanup.

> +
>  	masks = kcalloc(nvecs, sizeof(*masks), GFP_KERNEL);
>  	if (!masks)
>  		goto out;
> @@ -143,12 +150,15 @@ irq_create_affinity_masks(int nvecs, const struct irq_affinity *affd)
>   * @maxvec:	The maximum number of vectors available
>   * @affd:	Description of the affinity requirements
>   */
> -int irq_calc_affinity_vectors(int maxvec, const struct irq_affinity *affd)
> +int irq_calc_affinity_vectors(int minvec, int maxvec, const struct irq_affinity *affd)

This function has a kernel-doc comment above it, and you're adding a
parameter, so please update the kernel-doc to match.

>  {
>  	int resv = affd->pre_vectors + affd->post_vectors;
>  	int vecs = maxvec - resv;
>  	int cpus;
>  
> +	if (resv > minvec)
> +		return 0;
> +
>  	/* Stabilize the cpumasks */
>  	get_online_cpus();
>  	cpus = cpumask_weight(cpu_online_mask);
> -- 
> 2.12.0
> 



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