Re: [PATCH RFC v2] platform/x86: p2sb: Allow p2sb_bar() calls during PCI device probe

Shinichiro Kawasaki
2023-12-15T07:34:44Z

On Dec 13, 2023 / 13:41, Bjorn Helgaas wrote:
> On Tue, Dec 12, 2023 at 08:47:46PM +0900, Shin'ichiro Kawasaki wrote:
> > p2sb_bar() unhides P2SB device to get resources from the device. It
> > guards the operation by locking pci_rescan_remove_lock so that parallel
> > rescans do not find the P2SB device. However, this lock causes deadlock
> > when PCI bus rescan is triggered by /sys/bus/pci/rescan. The rescan
> > locks pci_rescan_remove_lock and probes PCI devices. When PCI devices
> > call p2sb_bar() during probe, it locks pci_rescan_remove_lock again.
> > Hence the deadlock.
> >
> > To avoid the deadlock, do not lock pci_rescan_remove_lock in p2sb_bar().
> > Instead, do the lock at fs_initcall. Introduce p2sb_cache_resources()
> > for fs_initcall which gets and caches the P2SB resources. At p2sb_bar(),
> > refer the cache and return to the caller.
> > ...
>
> > +/* Cache BAR0 of P2SB device from function 0 ot 7 */
>
> s/ot/to/
>
> or even s/from function 0 ot 7/functions 0 to 7/
>
> > +static bool p2sb_invalid_resource(struct resource *res)
> > +{
> > + return res->flags == 0;
> > +}
>
> IMO this would read better as "p2sb_valid_resource()" with
> corresponding negation in the callers. But it doesn't matter either
> way.
>
> > + * p2sb_bar - Get Primary to Sideband (P2SB) bridge device BAR
> > + * @bus: PCI bus to communicate with
> > + * @devfn: PCI slot and function to communicate with
> > + * @mem: memory resource to be filled in
> > + *
> > + * if @bus is NULL, the bus 0 in domain 0 will be used.
>
> s/if/If/

Thank you Bjorn. Will reflect them to the next version.