Re: [PATCH] PCI: Release coalesced resource

[Bjorn Helgaas]

On Thu, May 25, 2023 at 04:32:48PM +0100, Ross Lagerwall wrote:
> When contiguous windows are coalesced, the resource is invalidated and
> consequently not added to the bus. However, it remains in the resource
> hierarchy:
> 
> ...
>   ef2fff00-ef2fffff : 0000:00:13.2
>     ef2fff00-ef2fffff : ehci_hcd
> 00000000-00000000 : PCI Bus 0000:00
> f0000000-f3ffffff : PCI MMCONFIG 0000 [bus 00-3f]
>   f0000000-f3ffffff : Reserved
> ...

I assume the "00000000-00000000 : PCI Bus 0000:00" is the problematic
part?  Is there anything in dmesg that shows the resources before they
were coalesced?

Is there an error message we could include here to link the problem
with the solution?

> In some cases (e.g. the Xen scratch region), this causes future calls to
> allocate_resource() to choose an inappropriate location which the caller
> cannot handle. Fix by releasing the resource and removing from the
> hierarchy.
> 
> Fixes: 7c3855c423b1 ("PCI: Coalesce host bridge contiguous apertures")

7c3855c423b1 appeared in v5.16, so we may need a stable tag?

> Signed-off-by: Ross Lagerwall <ross.lagerwall@xxxxxxxxxx>
> ---
>  drivers/pci/probe.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
> index 0b2826c4a832..00ed20ac0dd6 100644
> --- a/drivers/pci/probe.c
> +++ b/drivers/pci/probe.c
> @@ -997,8 +997,10 @@ static int pci_register_host_bridge(struct pci_host_bridge *bridge)
>  	resource_list_for_each_entry_safe(window, n, &resources) {
>  		offset = window->offset;
>  		res = window->res;
> -		if (!res->flags && !res->start && !res->end)
> +		if (!res->flags && !res->start && !res->end) {
> +			release_resource(res);
>  			continue;
> +		}
>  
>  		list_move_tail(&window->node, &bridge->windows);
>  
> -- 
> 2.31.1
>