Re: [patch V2 05/10] PCI/MSI: Switch to MSI descriptor locking to guard()

[Peter Zijlstra]

On Thu, Mar 13, 2025 at 06:55:12PM +0100, Thomas Gleixner wrote:
> On Thu, Mar 13 2025 at 15:50, Jonathan Cameron wrote:
> >> +	guard(msi_descs_lock)(&dev->dev);
> >> +	int ret = __msix_setup_interrupts(dev, entries, nvec, masks);
> >> +	if (ret)
> >> +		pci_free_msi_irqs(dev);
> >
> > It's not immediately obvious what this is undoing (i.e. where the alloc
> > is).  I think it is at least mostly the pci_msi_setup_msi_irqs in
> > __msix_setup_interrupts
> 
> It's a universal cleanup for all possible error cases.
> 
> > Why not handle the error in __msix_setup_interrupts and make that function
> > side effect free.  Does require gotos but in a function that isn't
> > doing any cleanup magic so should be fine.
> 
> I had the gotos first and then hated them. But you are right, it's better
> to have them than having the magic clean up at the call site.
> 
> I'll fold the delta patch below.
> 
> Thanks,
> 
>         tglx
> ---
> --- a/drivers/pci/msi/msi.c
> +++ b/drivers/pci/msi/msi.c
> @@ -671,19 +671,23 @@ static int __msix_setup_interrupts(struc
>  	int ret = msix_setup_msi_descs(dev, entries, nvec, masks);
>  
>  	if (ret)
> -		return ret;
> +		goto fail;
>  
>  	ret = pci_msi_setup_msi_irqs(dev, nvec, PCI_CAP_ID_MSIX);
>  	if (ret)
> -		return ret;
> +		goto fail;
>  
>  	/* Check if all MSI entries honor device restrictions */
>  	ret = msi_verify_entries(dev);
>  	if (ret)
> -		return ret;
> +		goto fail;
>  
>  	msix_update_entries(dev, entries);
>  	return 0;
> +
> +fail:
> +	pci_free_msi_irqs(dev);
> +	return ret;
>  }

How about something like:

int __msix_setup_interrupts(struct device *_dev,... )
{
	struct device *dev __free(msi_irqs) = _dev;

	int ret = msix_setup_msi_descs(dev, entries, nvec, masks);
	if (ret)
		return ret;

	ret = pci_msi_setup_msi_irqs(dev, nvec, PCI_CAP_ID_MSIX);
	if (ret)
		return ret;

	/* Check if all MSI entries honor device restrictions */
	ret = msi_verify_entries(dev);
	if (ret)
		return ret;

	retain_ptr(dev);
	msix_update_entries(dev, entries);
	return 0;
}

?