Re: [PATCH v2] PCI: vmd: Fix spinlock usage on config access for RT kernel

Sebastian Andrzej Siewior
2024-12-18T15:48:41Z

On 2024-12-18 08:36:54 [-0700], Keith Busch wrote:
> On Wed, Dec 18, 2024 at 08:59:51PM +0900, Ryo Takakura wrote:
> > PCI config access is locked with pci_lock which serializes
> > pci_user/bus_write_config*() and pci_user/bus_read_config*().
> > The subsequently invoked vmd_pci_write() and vmd_pci_read() are also
> > serialized as they are only invoked by them respectively.
> >
> > Remove cfg_lock which is taken by vmd_pci_write() and vmd_pci_read()
> > for their serialization as its already serialized by pci_lock.
>
> That's only true if CONFIG_PCI_LOCKLESS_CONFIG isn't set, so pci_lock
> won't help with concurrent kernel config access in such a setup. I think
> the previous change to raw lock proposal was the correct approach.

I overlooked that. Wouldn't it make sense to let the vmd driver select
that option rather than adding/ having a lock for the same purpose?

Sebastian