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

Bjorn Helgaas
2023-12-13T19:41:48Z

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/