ACK: [SRU][F][PATCH 1/1] s390/pci: fix hot-plug of PCI function missing bus

[Andrea Righi]

On Thu, Nov 12, 2020 at 10:44:29AM +0100, frank.heimes at canonical.com wrote:
> From: Niklas Schnelle <schnelle at linux.ibm.com>
> 
> BugLink: https://bugs.launchpad.net/bugs/1903682
> 
> Under some circumstances in particular with "Reconfigure I/O Path"
> a zPCI function may first appear in Standby through a PCI event with
> PEC 0x0302 which initially makes it visible to the zPCI subsystem,
> Only after that is it configured with a zPCI event  with PEC 0x0301.
> If the zbus is still missing a PCI function zero (devfn == 0) when the
> PCI event 0x0301 is handled zdev->zbus->bus is still NULL and gets
> dereferenced in common code.
> Check for this case and enable but don't scan the zPCI function.
> This matches what would happen if we immediately got the 0x0301
> configuration request or the function was included in CLP List PCI.
> In all cases the PCI functions with devfn != 0 will be scanned once
> function 0 appears.
> 
> Fixes: 3047766bc6ec ("s390/pci: fix enabling a reserved PCI function")
> Cc: <stable at vger.kernel.org> # 5.8
> Signed-off-by: Niklas Schnelle <schnelle at linux.ibm.com>
> Acked-by: Pierre Morel <pmorel at linux.ibm.com>
> Signed-off-by: Heiko Carstens <hca at linux.ibm.com>
> (cherry picked from commit 0b2ca2c7d0c9e2731d01b6c862375d44a7e13923)
> Signed-off-by: Frank Heimes <frank.heimes at canonical.com>

Clean upstream cherry pick that fixes a potential NULL pointer
derfererence. Looks good to me.

Acked-by: Andrea Righi <andrea.righi at canonical.com>