Subject: Re: [PATCH 3/4] powerpc/eeh: Remove workaround from eeh_add_device_late()

From: Sam Bobroff <[email-masked]>
Date: Wed, 8 Apr 2020 16:21:59 +1000

On Fri, Apr 03, 2020 at 05:08:32PM +1100, Oliver O'Halloran wrote:
> On Mon, 2020-03-30 at 15:56 +1100, Sam Bobroff wrote:
> > When EEH device state was released asynchronously by the device
> > release handler, it was possible for an outstanding reference to
> > prevent it's release and it was necessary to work around that if a
> > device was re-discovered at the same PCI location.
> 
> I think this is a bit misleading. The main situation where you'll hit
> this hack is when recovering a device with a driver that doesn't
> implement the error handling callbacks. In that case the device is
> removed, reset, then re-probed by the PCI core, but we assume it's the
> same physical device so the eeh_device state remains active.
> 
> If you actually changed the underlying device I suspect something bad
> would happen.

I'm not sure I understand. Isn't the case you're talking about caught by
the earlier check (just above the patch)?

	if (edev->pdev == dev) {
		eeh_edev_dbg(edev, "Device already referenced!\n");
		return;
	}
> 
> > Now that the state is released synchronously that is no longer
> > possible and the workaround is no longer necessary.
> 
> You could probably fold this into the previous patch, but eh. You could
> probably fold this into the previous patch, but eh.

True.

> > Signed-off-by: Sam Bobroff <[email-masked]>
> > ---
> >  arch/powerpc/kernel/eeh.c | 23 +----------------------
> >  1 file changed, 1 insertion(+), 22 deletions(-)
> > 
> > diff --git a/arch/powerpc/kernel/eeh.c b/arch/powerpc/kernel/eeh.c
> > index c36c5a7db5ca..12c248a16527 100644
> > --- a/arch/powerpc/kernel/eeh.c
> > +++ b/arch/powerpc/kernel/eeh.c
> > @@ -1206,28 +1206,7 @@ void eeh_add_device_late(struct pci_dev *dev)
> >  		eeh_edev_dbg(edev, "Device already referenced!\n");
> >  		return;
> >  	}
> > -
> > -	/*
> > -	 * The EEH cache might not be removed correctly because of
> > -	 * unbalanced kref to the device during unplug time, which
> > -	 * relies on pcibios_release_device(). So we have to remove
> > -	 * that here explicitly.
> > -	 */
> > -	if (edev->pdev) {
> > -		eeh_rmv_from_parent_pe(edev);
> > -		eeh_addr_cache_rmv_dev(edev->pdev);
> > -		eeh_sysfs_remove_device(edev->pdev);
> > -
> > -		/*
> > -		 * We definitely should have the PCI device removed
> > -		 * though it wasn't correctly. So we needn't call
> > -		 * into error handler afterwards.
> > -		 */
> > -		edev->mode |= EEH_DEV_NO_HANDLER;
> > -
> > -		edev->pdev = NULL;
> > -		dev->dev.archdata.edev = NULL;
> > -	}
> > +	WARN_ON_ONCE(edev->pdev);
> >  
> >  	if (eeh_has_flag(EEH_PROBE_MODE_DEV))
> >  		eeh_ops->probe(pdn, NULL);
>