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

Peter Zijlstra
2025-03-14T09:43:00Z

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;
}

?