Re: [PATCH v15 3/9] PCI/AER: Handle ERR_FATAL with removal and re-enumeration of devices

From: poza
Date: Thu May 10 2018 - 10:18:56 EST

On 2018-05-10 18:45, okaya@xxxxxxxxxxxxxx wrote:
On 2018-05-10 14:10, Bjorn Helgaas wrote:
On Thu, May 10, 2018 at 12:31:16PM +0530, poza@xxxxxxxxxxxxxx wrote:
On 2018-05-10 04:51, Bjorn Helgaas wrote:
> On Wed, May 09, 2018 at 06:44:53PM +0530, poza@xxxxxxxxxxxxxx wrote:
> > On 2018-05-09 18:37, Bjorn Helgaas wrote:
> > > On Tue, May 08, 2018 at 06:53:30PM -0500, Bjorn Helgaas wrote:
> > > > On Thu, May 03, 2018 at 01:03:52AM -0400, Oza Pawandeep wrote:
> > > > > This patch alters the behavior of handling of ERR_FATAL, where removal
> > > > > of devices is initiated, followed by reset link, followed by
> > > > > re-enumeration.
> > > > >
> > > > > So the errors are handled in a different way as follows:
> > > > > ERR_NONFATAL => call driver recovery entry points
> > > > > ERR_FATAL => remove and re-enumerate
> > > > >
> > > > > please refer to Documentation/PCI/pci-error-recovery.txt for more details.
> > > > >
> > > > > Signed-off-by: Oza Pawandeep <poza@xxxxxxxxxxxxxx>
> > > > >
> > > > > diff --git a/drivers/pci/pcie/aer/aerdrv.c b/drivers/pci/pcie/aer/aerdrv.c
> > > > > index 779b387..206f590 100644
> > > > > --- a/drivers/pci/pcie/aer/aerdrv.c
> > > > > +++ b/drivers/pci/pcie/aer/aerdrv.c
> > > > > @@ -330,6 +330,13 @@ static pci_ers_result_t aer_root_reset(struct pci_dev *dev)
> > > > > reg32 |= ROOT_PORT_INTR_ON_MESG_MASK;
> > > > > pci_write_config_dword(dev, pos + PCI_ERR_ROOT_COMMAND, reg32);
> > > > >
> > > > > + /*
> > > > > + * This function is called only on ERR_FATAL now, and since
> > > > > + * the pci_report_resume is called only in ERR_NONFATAL case,
> > > > > + * the clearing part has to be taken care here.
> > > > > + */
> > > > > + aer_error_resume(dev);
> > > >
> > > > I don't understand this part. Previously the ERR_FATAL path looked
> > > > like
> > > > this:
> > > >
> > > > do_recovery
> > > > reset_link
> > > > driver->reset_link
> > > > aer_root_reset
> > > > pci_reset_bridge_secondary_bus # <-- reset
> > > > broadcast_error_message(..., report_resume)
> > > > pci_walk_bus(..., report_resume, ...)
> > > > report_resume
> > > > if (cb == report_resume)
> > > > pci_cleanup_aer_uncorrect_error_status
> > > > pci_write_config_dword(PCI_ERR_UNCOR_STATUS) # <-- clear
> > > > status
> > > >
> > > > After this patch, it will look like this:
> > > >
> > > > do_recovery
> > > > do_fatal_recovery
> > > > pci_cleanup_aer_uncorrect_error_status
> > > > pci_write_config_dword(PCI_ERR_UNCOR_STATUS) # <-- clear
> > > > status
> > > > reset_link
> > > > driver->reset_link
> > > > aer_root_reset
> > > > pci_reset_bridge_secondary_bus # <-- reset
> > > > aer_error_resume
> > > > pcie_capability_write_word(PCI_EXP_DEVSTA) #
> > > > <-- clear more
> > > > pci_write_config_dword(PCI_ERR_UNCOR_STATUS) #
> > > > <-- clear status
> > > >
> > > > So if I'm understanding correctly, the new path clears the status too
> > > > early, then clears it again (plus clearing DEVSTA, which we didn't do
> > > > before) later.
> > > >
> > > > I would think we would want to leave aer_root_reset() alone, and
> > > > just move
> > > > the pci_cleanup_aer_uncorrect_error_status() in do_fatal_recovery()
> > > > down so
> > > > it happens after we call reset_link(). That way the reset/clear
> > > > sequence
> > > > would be the same as it was before.
> > >
> > > I've been fiddling with this a bit myself and will post the results to
> > > see
> > > what you think.
> >
> >
> > ok so you are suggesting to move
> > pci_cleanup_aer_uncorrect_error_status down
> > which I can do.
> >
> > And not to call aer_error_resume, because you think its clearing the
> > status
> > again.
> >
> > following code: calls aer_error_resume.
> > pci_broadcast_error_message()
> > /*
> > * If the error is reported by an end point, we
> > think this
> > * error is related to the upstream link of the end
> > point.
> > */
> > if (state == pci_channel_io_normal)
> > /*
> > * the error is non fatal so the bus is ok,
> > just
> > invoke
> > * the callback for the function that logged
> > the
> > error.
> > */
> > cb(dev, &result_data);
> > else
> > pci_walk_bus(dev->bus, cb, &result_data);
>
> Holy crap, I thought this could not possibly get any more complicated,
> but you're right; we do actually call aer_error_resume() today via an
> extremely convoluted path:
>
> do_recovery(pci_dev)
> broadcast_error_message(..., error_detected, ...)
> if (AER_FATAL)
> reset_link(pci_dev)
> udev = BRIDGE ? pci_dev : pci_dev->bus->self
> driver->reset_link(udev)
> aer_root_reset(udev)
> if (CAN_RECOVER)
> broadcast_error_message(..., mmio_enabled, ...)
> if (NEED_RESET)
> broadcast_error_message(..., slot_reset, ...)
> broadcast_error_message(dev, ..., report_resume, ...)
> if (BRIDGE)
> report_resume
> driver->resume
> pcie_portdrv_err_resume
> device_for_each_child(..., resume_iter)
> resume_iter
> driver->error_resume
> aer_error_resume
> pci_cleanup_aer_uncorrect_error_status(pci_dev) # only if
> BRIDGE
> pci_write_config_dword(PCI_ERR_UNCOR_STATUS)
>
> aerdriver is the only port service driver that implements
> .error_resume(), and aerdriver only binds to root ports. I can't
> really believe all these device_for_each_child()/resume_iter()
> gyrations are necessary when this is AER code calling AER code.
>
> Bjorn

here is the code of do_fatal_recovery, where I have moved the things down
and doing only if it is bridge.
let me know how this looks to you, so then I can post v16.

This looks superficially OK. It is very difficult for me to verify that
the behavior is equivalent to the current code, but that's not your fault;
it's just a consequence of the existing design.

I have a couple trivial comments elsewhere, and I'll respond to those
patches individually.

static pci_ers_result_t do_fatal_recovery(struct pci_dev *dev, int severity)
{
struct pci_dev *udev;
struct pci_bus *parent;
struct pci_dev *pdev, *temp;
struct aer_broadcast_data result_data;
pci_ers_result_t result = PCI_ERS_RESULT_RECOVERED;


if (dev->hdr_type == PCI_HEADER_TYPE_BRIDGE)
udev = dev;
else
udev = dev->bus->self;

parent = udev->subordinate;
pci_lock_rescan_remove();
list_for_each_entry_safe_reverse(pdev, temp, &parent->devices,
bus_list) {
pci_dev_get(pdev);
pci_dev_set_disconnected(pdev, NULL);
if (pci_has_subordinate(pdev))
pci_walk_bus(pdev->subordinate,
pci_dev_set_disconnected, NULL);
pci_stop_and_remove_bus_device(pdev);
pci_dev_put(pdev);
}

result = reset_link(udev, severity);
if (severity == AER_FATAL && dev->hdr_type ==
PCI_HEADER_TYPE_BRIDGE) {
pci_walk_bus(dev->subordinate, report_resume, &result_data);

Why are we calling resume?

the reason we have to call resume here, because we are not calling aer_resume() any more in root_reset.
and we have to call resume only in bridge case.
please have a look at couple of conversation back with Bjorn.
the objective is to align the sequence close to the current code.


pci_cleanup_aer_uncorrect_error_status(dev);
dev->error_state = pci_channel_io_normal;
}
if (result == PCI_ERS_RESULT_RECOVERED)
if (pcie_wait_for_link(udev, true))
pci_rescan_bus(udev->bus);

pci_unlock_rescan_remove();

return result;
}

Regards,
Oza.