On Wed, Apr 08, 2020 at 04:53:36PM +1000, Oliver O'Halloran wrote:

On Wed, Apr 8, 2020 at 4:22 PM Sam Bobroff [off-list ref] wrote:

quoted

On Fri, Apr 03, 2020 at 05:08:32PM +1100, Oliver O'Halloran wrote:

quoted

On Mon, 2020-03-30 at 15:56 +1100, Sam Bobroff wrote:

quoted

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;
        }

No, in the case I'm talking about the pci_dev is torn down and
freed(). After the PE is reset we re-probe the device and create a new
pci_dev.  If the release of the old pci_dev is delayed we need the
hack this patch is removing.

Oh, yes, that is the case I was intending to change here.  But I must be
missing something, isn't it also the case that's changed by patch 2/4?

What I intended was, after patch 2, eeh_remove_device() is called from
the bus notifier so it happens imediately when recovery calls
pci_stop_and_remove_bus_device().  Once it returns, edev->pdev has
already been set to NULL by eeh_remove_device() so this case can't be
hit anymore, and we should clean it up (this patch).

(There is a slight difference in the way EEH_PE_KEEP is handled between
the code removed here and the body of eeh_remove_device(), but checking
and explaining that is already on my list for v2.)

(I did test recovery on an unaware device and didn't hit the
WARN_ON_ONCE().)

The check above should probably be a WARN_ON() since we should never
be re-running the EEH probe on the same device. I think there is a
case where that can happen, but I don't remember the details.

Yeah, I also certainly see the "Device already referenced!" message
while debugging, and it would be good to track down.

Oliver