Re: [PATCH] PCI: pciehp: Fix NULL pointer dereference in pciehp_configure_device()

[Lukas Wunner]

On Mon, Nov 09, 2026 at 09:53:38PM +0000, Priyank Rathod wrote:
> On Mon, Oct 12, 2026 at 10:16:29PM +0000, sashiko-bot@xxxxxxxxxx wrote:
> > While this allows devices without Function 0 to be successfully hot-added,
> > will it lead to spurious teardowns upon system resume?
> ...
> > Could this spurious teardown issue be avoided by modifying
> > pciehp_device_replaced() to handle missing Function 0 devices correctly?
[...]
> Regarding the bot's question above: pciehp assumes Function 0
> (PCI_DEVFN(0, 0)) represents an occupied slot across all four of its
> lookup sites -- the -EEXIST check at the top of
> pciehp_configure_device(), pcie_init(), pciehp_device_replaced(), and
> the DSN read at the end of pciehp_configure_device() (consistent with
> PCIe r6.3 sec 7.9.3 requiring Multi-Function Devices implementing DSN to
> expose it on Function 0).

I'm not even sure whether pciehp is actually used with jailhouse,
s390 or loongarch.  pciehp assumes in multiple places that function 0
is present, so guarding against a missing function 0 in a single place
doesn't really make sense.

Note that there's a patch pending which moves the cached dsn from
pciehp's struct controller to struct pci_dev, so the days are numbered
for the lines you're changing:

https://lore.kernel.org/r/20260902133933.2992457-7-terry.bowman@xxxxxxx/

Are you actually observing a crash in practice because of a missing NULL
pointer check?

Thanks,

Lukas