Re: [patch V4 08/14] PCI/MSI: Switch msi_capability_init() to guard(msi_desc_lock)

[Bjorn Helgaas]

On Wed, Mar 19, 2025 at 11:56:53AM +0100, Thomas Gleixner wrote:
> Split the lock protected functionality of msi_capability_init() out into a
> helper function and use guard(msi_desc_lock) to replace the lock/unlock
> pair.
> 
> No functional change intended.
> 
> Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>

Acked-by: Bjorn Helgaas <bhelgaas@xxxxxxxxxx>

> ---
> V4: Split out from the previous combo patch
> ---
>  drivers/pci/msi/msi.c |   68 ++++++++++++++++++++++++++------------------------
>  1 file changed, 36 insertions(+), 32 deletions(-)
> 
> --- a/drivers/pci/msi/msi.c
> +++ b/drivers/pci/msi/msi.c
> @@ -336,38 +336,13 @@ static int msi_verify_entries(struct pci
>  	return !entry ? 0 : -EIO;
>  }
>  
> -/**
> - * msi_capability_init - configure device's MSI capability structure
> - * @dev: pointer to the pci_dev data structure of MSI device function
> - * @nvec: number of interrupts to allocate
> - * @affd: description of automatic IRQ affinity assignments (may be %NULL)
> - *
> - * Setup the MSI capability structure of the device with the requested
> - * number of interrupts.  A return value of zero indicates the successful
> - * setup of an entry with the new MSI IRQ.  A negative return value indicates
> - * an error, and a positive return value indicates the number of interrupts
> - * which could have been allocated.
> - */
> -static int msi_capability_init(struct pci_dev *dev, int nvec,
> -			       struct irq_affinity *affd)
> +static int __msi_capability_init(struct pci_dev *dev, int nvec, struct irq_affinity_desc *masks)
>  {
> +	int ret = msi_setup_msi_desc(dev, nvec, masks);
>  	struct msi_desc *entry, desc;
> -	int ret;
> -
> -	/* Reject multi-MSI early on irq domain enabled architectures */
> -	if (nvec > 1 && !pci_msi_domain_supports(dev, MSI_FLAG_MULTI_PCI_MSI, ALLOW_LEGACY))
> -		return 1;
> -
> -	/* Disable MSI during setup in the hardware to erase stale state */
> -	pci_msi_set_enable(dev, 0);
>  
> -	struct irq_affinity_desc *masks __free(kfree) =
> -		affd ? irq_create_affinity_masks(nvec, affd) : NULL;
> -
> -	msi_lock_descs(&dev->dev);
> -	ret = msi_setup_msi_desc(dev, nvec, masks);
>  	if (ret)
> -		goto unlock;
> +		return ret;
>  
>  	/* All MSIs are unmasked by default; mask them all */
>  	entry = msi_first_desc(&dev->dev, MSI_DESC_ALL);
> @@ -395,16 +370,45 @@ static int msi_capability_init(struct pc
>  
>  	pcibios_free_irq(dev);
>  	dev->irq = entry->irq;
> -	goto unlock;
> -
> +	return 0;
>  err:
>  	pci_msi_unmask(&desc, msi_multi_mask(&desc));
>  	pci_free_msi_irqs(dev);
> -unlock:
> -	msi_unlock_descs(&dev->dev);
>  	return ret;
>  }
>  
> +/**
> + * msi_capability_init - configure device's MSI capability structure
> + * @dev: pointer to the pci_dev data structure of MSI device function
> + * @nvec: number of interrupts to allocate
> + * @affd: description of automatic IRQ affinity assignments (may be %NULL)
> + *
> + * Setup the MSI capability structure of the device with the requested
> + * number of interrupts.  A return value of zero indicates the successful
> + * setup of an entry with the new MSI IRQ.  A negative return value indicates
> + * an error, and a positive return value indicates the number of interrupts
> + * which could have been allocated.
> + */
> +static int msi_capability_init(struct pci_dev *dev, int nvec,
> +			       struct irq_affinity *affd)
> +{
> +	/* Reject multi-MSI early on irq domain enabled architectures */
> +	if (nvec > 1 && !pci_msi_domain_supports(dev, MSI_FLAG_MULTI_PCI_MSI, ALLOW_LEGACY))
> +		return 1;
> +
> +	/*
> +	 * Disable MSI during setup in the hardware, but mark it enabled
> +	 * so that setup code can evaluate it.
> +	 */
> +	pci_msi_set_enable(dev, 0);
> +
> +	struct irq_affinity_desc *masks __free(kfree) =
> +		affd ? irq_create_affinity_masks(nvec, affd) : NULL;
> +
> +	guard(msi_descs_lock)(&dev->dev);
> +	return __msi_capability_init(dev, nvec, masks);
> +}
> +
>  int __pci_enable_msi_range(struct pci_dev *dev, int minvec, int maxvec,
>  			   struct irq_affinity *affd)
>  {
>