Re: [PATCH 2/5 V2] PCI: pciehp: check and wait port status out of DPC before handling DLLSC and PDC

[Lukas Wunner]

On Sun, Sep 27, 2020 at 11:27:46AM -0400, Sinan Kaya wrote:
> On 9/26/2020 11:28 PM, Ethan Zhao wrote:
> > --- a/drivers/pci/hotplug/pciehp_hpc.c
> > +++ b/drivers/pci/hotplug/pciehp_hpc.c
> > @@ -710,8 +710,10 @@ static irqreturn_t pciehp_ist(int irq, void *dev_id)
> >  	down_read(&ctrl->reset_lock);
> >  	if (events & DISABLE_SLOT)
> >  		pciehp_handle_disable_request(ctrl);
> > -	else if (events & (PCI_EXP_SLTSTA_PDC | PCI_EXP_SLTSTA_DLLSC))
> > +	else if (events & (PCI_EXP_SLTSTA_PDC | PCI_EXP_SLTSTA_DLLSC)) {
> > +		pci_wait_port_outdpc(pdev);
> >  		pciehp_handle_presence_or_link_change(ctrl, events);
> > +	}
> >  	up_read(&ctrl->reset_lock);
> 
> This looks like a hack TBH.
> 
> Lukas, Keith;
> 
> What is your take on this?
> Why is device lock not protecting this situation?
> 
> Is there a lock missing in hotplug driver?

According to Ethan's commit message, there are two issues here:
One, that pciehp may remove a device even though DPC recovered the error,
and two, that a null pointer deref occurs.

The latter is most certainly not a locking issue but failure of DPC
to hold a reference on the pci_dev.

Thanks,

Lukas