Re: [PATCH v5 4/5] PCI: endpoint: pci-epf-vntb: Switch vpci_scan_bus() to use pci_scan_root_bus()

[Koichiro Den]

On Mon, Mar 02, 2026 at 09:39:26PM +0530, Manivannan Sadhasivam wrote:
> On Thu, Feb 26, 2026 at 05:41:41PM +0900, Koichiro Den wrote:
> > vpci_scan_bus() currently uses pci_scan_bus(), which creates a root bus
> > without a parent struct device. In a subsequent change we want to tear
> > down the virtual PCI root bus using pci_remove_root_bus(). For that to
> > work correctly, the root bus must be associated with a parent device,
> > similar to what the removed pci_scan_bus_parented() helper used to do.
> > 
> > Switch vpci_scan_bus() to use pci_scan_root_bus() and pass
> > &ndev->epf->epc->dev as the parent. Build the resource list in the same
> > way as pci_scan_bus(), so the behavior is unchanged except that the
> > virtual root bus now has a proper parent device. This avoids crashes in
> > the pci_epf_unbind() -> epf_ntb_unbind() -> pci_remove_root_bus() ->
> > pci_bus_release_domain_nr() path once we start removing the root bus in
> > a follow-up patch.
> > 
> > Reviewed-by: Frank Li <Frank.Li@xxxxxxx>
> > Signed-off-by: Koichiro Den <den@xxxxxxxxxxxxx>
> > ---
> > Changes since v4:
> >   - Correct the subject prefix
> >     s/NTB: epf: vntb:/PCI: endpoint: pci-epf-vntb:/
> > 
> >  drivers/pci/endpoint/functions/pci-epf-vntb.c | 15 +++++++++++++--
> >  1 file changed, 13 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/pci/endpoint/functions/pci-epf-vntb.c b/drivers/pci/endpoint/functions/pci-epf-vntb.c
> > index 805353528967..f353e9a57194 100644
> > --- a/drivers/pci/endpoint/functions/pci-epf-vntb.c
> > +++ b/drivers/pci/endpoint/functions/pci-epf-vntb.c
> > @@ -1220,8 +1220,19 @@ static int vpci_scan_bus(void *sysdata)
> >  {
> >  	struct pci_bus *vpci_bus;
> >  	struct epf_ntb *ndev = sysdata;
> > -
> > -	vpci_bus = pci_scan_bus(ndev->vbus_number, &vpci_ops, sysdata);
> > +	LIST_HEAD(resources);
> > +	static struct resource busn_res = {
> > +		.start = 0,
> > +		.end = 255,
> > +		.flags = IORESOURCE_BUS,
> > +	};
> > +
> > +	pci_add_resource(&resources, &ioport_resource);
> > +	pci_add_resource(&resources, &iomem_resource);
> > +	pci_add_resource(&resources, &busn_res);
> > +
> > +	vpci_bus = pci_scan_root_bus(&ndev->epf->epc->dev, ndev->vbus_number,
> > +				     &vpci_ops, sysdata, &resources);
> 
> Don't you need pci_lock_rescan_remove()/pci_unlock_rescan_remove()?

Yes, we do need them. Thanks for pointing this out.

This locking was already missing before this series (when vpci_scan_bus() used
pci_scan_bus()), so I'll add a separate fix patch between Patch 3 and Patch 4,
likely with:
Fixes: e35f56bb0330 ("PCI: endpoint: Support NTB transfer between RC and EP").

---8<---
diff --git a/drivers/pci/endpoint/functions/pci-epf-vntb.c b/drivers/pci/endpoint/functions/pci-epf-vntb.c
index 805353528967..469b6e2b8d45 100644
--- a/drivers/pci/endpoint/functions/pci-epf-vntb.c
+++ b/drivers/pci/endpoint/functions/pci-epf-vntb.c
@@ -1221,14 +1221,19 @@ static int vpci_scan_bus(void *sysdata)
        struct pci_bus *vpci_bus;
        struct epf_ntb *ndev = sysdata;

+       pci_lock_rescan_remove();
+
        vpci_bus = pci_scan_bus(ndev->vbus_number, &vpci_ops, sysdata);
        if (!vpci_bus) {
                pr_err("create pci bus failed\n");
+               pci_unlock_rescan_remove();
                return -EINVAL;
        }

        pci_bus_add_devices(vpci_bus);

+       pci_unlock_rescan_remove();
+
        return 0;
 }

---8<---

Also, while respinning, I'll fix the error path in the pci_scan_root_bus()
version to free the temporary resource list when pci_scan_root_bus() fails,
since it doesn't free it on behalf of the caller. I noticed this while
revisiting the patch.

Best regards,
Koichiro

> 
> - Mani
> 
> -- 
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