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

[Bjorn Helgaas <helgaas@kernel.org>]

On Thu, May 10, 2018 at 12:31:16PM +0530, poza@codeaurora.org wrote:
> On 2018-05-10 04:51, Bjorn Helgaas wrote:
> > On Wed, May 09, 2018 at 06:44:53PM +0530, poza@codeaurora.org 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@codeaurora.org>
> > > > > >
> > > > > > 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);
>                 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.
> 
>