Re: [PATCH v16 8/9] PCI/DPC: Unify and plumb error handling into DPC

Bjorn Helgaas
2018-05-16T13:04:55Z

On Wed, May 16, 2018 at 05:45:58PM +0530, poza@codeaurora.org wrote:
> On 2018-05-16 16:22, Bjorn Helgaas wrote:
> > On Wed, May 16, 2018 at 01:46:25PM +0530, poza@codeaurora.org wrote:
> > > On 2018-05-16 05:26, Bjorn Helgaas wrote:
> > > > On Fri, May 11, 2018 at 05:22:08PM +0530, poza@codeaurora.org wrote:
> > > > > On 2018-05-11 16:13, Oza Pawandeep wrote:
> > > > > > DPC driver implements link_reset callback, and calls
> > > > > > pci_do_fatal_recovery().
> > > > > >
> > > > > > Which follows standard path of ERR_FATAL recovery.
> > > > > >
> > > > > > Signed-off-by: Oza Pawandeep <poza@codeaurora.org>
> > > > > >
> > > > > > diff --git a/drivers/pci/pci.h b/drivers/pci/pci.h
> > > > > > index 5e8857a..6af7595 100644
> > > > > > --- a/drivers/pci/pci.h
> > > > > > +++ b/drivers/pci/pci.h
> > > > > > @@ -354,7 +354,7 @@ static inline resource_size_t
> > > > > > pci_resource_alignment(struct pci_dev *dev,
> > > > > > void pci_enable_acs(struct pci_dev *dev);
> > > > > >
> > > > > > /* PCI error reporting and recovery */
> > > > > > -void pcie_do_fatal_recovery(struct pci_dev *dev);
> > > > > > +void pcie_do_fatal_recovery(struct pci_dev *dev, u32 service);
> > > > > > void pcie_do_nonfatal_recovery(struct pci_dev *dev);
> > > > > >
> > > > > > bool pcie_wait_for_link(struct pci_dev *pdev, bool active);
> > > > > > diff --git a/drivers/pci/pcie/aer/aerdrv_core.c
> > > > > > b/drivers/pci/pcie/aer/aerdrv_core.c
> > > > > > index fdfc474..36e622d 100644
> > > > > > --- a/drivers/pci/pcie/aer/aerdrv_core.c
> > > > > > +++ b/drivers/pci/pcie/aer/aerdrv_core.c
> > > > > > @@ -254,7 +254,7 @@ static void handle_error_source(struct pcie_device
> > > > > > *aerdev,
> > > > > > } else if (info->severity == AER_NONFATAL)
> > > > > > pcie_do_nonfatal_recovery(dev);
> > > > > > else if (info->severity == AER_FATAL)
> > > > > > - pcie_do_fatal_recovery(dev);
> > > > > > + pcie_do_fatal_recovery(dev, PCIE_PORT_SERVICE_AER);
> > > > > > }
> > > > > >
> > > > > > #ifdef CONFIG_ACPI_APEI_PCIEAER
> > > > > > @@ -321,7 +321,7 @@ static void aer_recover_work_func(struct work_struct
> > > > > > *work)
> > > > > > if (entry.severity == AER_NONFATAL)
> > > > > > pcie_do_nonfatal_recovery(pdev);
> > > > > > else if (entry.severity == AER_FATAL)
> > > > > > - pcie_do_fatal_recovery(pdev);
> > > > > > + pcie_do_fatal_recovery(pdev, PCIE_PORT_SERVICE_AER);
> > > > > > pci_dev_put(pdev);
> > > > > > }
> > > > > > }
> > > > > > diff --git a/drivers/pci/pcie/dpc.c b/drivers/pci/pcie/dpc.c
> > > > > > index 80ec384..5680c13 100644
> > > > > > --- a/drivers/pci/pcie/dpc.c
> > > > > > +++ b/drivers/pci/pcie/dpc.c
> > > > > > @@ -73,29 +73,31 @@ static void dpc_wait_link_inactive(struct dpc_dev
> > > > > > *dpc)
> > > > > > pcie_wait_for_link(pdev, false);
> > > > > > }
> > > > > >
> > > > > > -static void dpc_work(struct work_struct *work)
> > > > > > +static pci_ers_result_t dpc_reset_link(struct pci_dev *pdev)
> > > > > > {
> > > > > > - struct dpc_dev *dpc = container_of(work, struct dpc_dev, work);
> > > > > > - struct pci_dev *dev, *temp, *pdev = dpc->dev->port;
> > > > > > - struct pci_bus *parent = pdev->subordinate;
> > > > > > - u16 cap = dpc->cap_pos, ctl;
> > > > > > -
> > > > > > - pci_lock_rescan_remove();
> > > > > > - list_for_each_entry_safe_reverse(dev, temp, &parent->devices,
> > > > > > - bus_list) {
> > > > > > - pci_dev_get(dev);
> > > > > > - pci_dev_set_disconnected(dev, NULL);
> > > > > > - if (pci_has_subordinate(dev))
> > > > > > - pci_walk_bus(dev->subordinate,
> > > > > > - pci_dev_set_disconnected, NULL);
> > > > > > - pci_stop_and_remove_bus_device(dev);
> > > > > > - pci_dev_put(dev);
> > > > > > - }
> > > > > > - pci_unlock_rescan_remove();
> > > > > > -
> > > > > > + struct dpc_dev *dpc;
> > > > > > + struct pcie_device *pciedev;
> > > > > > + struct device *devdpc;
> > > > > > + u16 cap, ctl;
> > > > > > +
> > > > > > + /*
> > > > > > + * DPC disables the Link automatically in hardware, so it has
> > > > > > + * already been reset by the time we get here.
> > > > > > + */
> > > > > > +
> > > > > > + devdpc = pcie_port_find_device(pdev, PCIE_PORT_SERVICE_DPC);
> > > > > > + pciedev = to_pcie_device(devdpc);
> > > > > > + dpc = get_service_data(pciedev);
> > > > > > + cap = dpc->cap_pos;
> > > > > > +
> > > > > > + /*
> > > > > > + * Waiting until the link is inactive, then clearing DPC
> > > > > > + * trigger status to allow the port to leave DPC.
> > > > > > + */
> > > > > > dpc_wait_link_inactive(dpc);
> > > > > > +
> > > > > > if (dpc->rp_extensions && dpc_wait_rp_inactive(dpc))
> > > > > > - return;
> > > > > > + return PCI_ERS_RESULT_DISCONNECT;
> > > > > > if (dpc->rp_extensions && dpc->rp_pio_status) {
> > > > > > pci_write_config_dword(pdev, cap + PCI_EXP_DPC_RP_PIO_STATUS,
> > > > > > dpc->rp_pio_status);
> > > > > > @@ -108,6 +110,17 @@ static void dpc_work(struct work_struct *work)
> > > > > > pci_read_config_word(pdev, cap + PCI_EXP_DPC_CTL, &ctl);
> > > > > > pci_write_config_word(pdev, cap + PCI_EXP_DPC_CTL,
> > > > > > ctl | PCI_EXP_DPC_CTL_INT_EN);
> > > > > > +
> > > > > > + return PCI_ERS_RESULT_RECOVERED;
> > > > > > +}
> > > > > > +
> > > > > > +static void dpc_work(struct work_struct *work)
> > > > > > +{
> > > > > > + struct dpc_dev *dpc = container_of(work, struct dpc_dev, work);
> > > > > > + struct pci_dev *pdev = dpc->dev->port;
> > > > > > +
> > > > > > + /* From DPC point of view error is always FATAL. */
> > > > > > + pcie_do_fatal_recovery(pdev, PCIE_PORT_SERVICE_DPC);
> > > > > > }
> > > > > >
> > > > > > static void dpc_process_rp_pio_error(struct dpc_dev *dpc)
> > > > > > @@ -288,6 +301,7 @@ static struct pcie_port_service_driver dpcdriver = {
> > > > > > .service = PCIE_PORT_SERVICE_DPC,
> > > > > > .probe = dpc_probe,
> > > > > > .remove = dpc_remove,
> > > > > > + .reset_link = dpc_reset_link,
> > > > > > };
> > > > > >
> > > > > > static int __init dpc_service_init(void)
> > > > > > diff --git a/drivers/pci/pcie/err.c b/drivers/pci/pcie/err.c
> > > > > > index 33a16b1..29ff148 100644
> > > > > > --- a/drivers/pci/pcie/err.c
> > > > > > +++ b/drivers/pci/pcie/err.c
> > > > > > @@ -185,7 +185,7 @@ static pci_ers_result_t default_reset_link(struct
> > > > > > pci_dev *dev)
> > > > > > return PCI_ERS_RESULT_RECOVERED;
> > > > > > }
> > > > > >
> > > > > > -static pci_ers_result_t reset_link(struct pci_dev *dev)
> > > > > > +static pci_ers_result_t reset_link(struct pci_dev *dev, u32 service)
> > > > > > {
> > > > > > struct pci_dev *udev;
> > > > > > pci_ers_result_t status;
> > > > > > @@ -200,7 +200,7 @@ static pci_ers_result_t reset_link(struct pci_dev
> > > > > > *dev)
> > > > > > }
> > > > > >
> > > > > > /* Use the aer driver of the component firstly */
> > > > > > - driver = pcie_port_find_service(udev, PCIE_PORT_SERVICE_AER);
> > > > > > + driver = pcie_port_find_service(udev, service);
> > > > > >
> > > > > > if (driver && driver->reset_link) {
> > > > > > status = driver->reset_link(udev);
> > > > > > @@ -287,7 +287,7 @@ static pci_ers_result_t
> > > > > > broadcast_error_message(struct pci_dev *dev,
> > > > > > * followed by re-enumeration of devices.
> > > > > > */
> > > > > >
> > > > > > -void pcie_do_fatal_recovery(struct pci_dev *dev)
> > > > > > +void pcie_do_fatal_recovery(struct pci_dev *dev, u32 service)
> > > > > > {
> > > > > > struct pci_dev *udev;
> > > > > > struct pci_bus *parent;
> > > > > > @@ -313,7 +313,7 @@ void pcie_do_fatal_recovery(struct pci_dev *dev)
> > > > > > pci_dev_put(pdev);
> > > > > > }
> > > > > >
> > > > > > - result = reset_link(udev);
> > > > > > + result = reset_link(udev, service);
> > > > > >
> > > > > > if (dev->hdr_type == PCI_HEADER_TYPE_BRIDGE) {
> > > > > > /*
> > > > > > diff --git a/include/linux/aer.h b/include/linux/aer.h
> > > > > > index 8f87bbe..0c506fe 100644
> > > > > > --- a/include/linux/aer.h
> > > > > > +++ b/include/linux/aer.h
> > > > > > @@ -14,6 +14,7 @@
> > > > > > #define AER_NONFATAL 0
> > > > > > #define AER_FATAL 1
> > > > > > #define AER_CORRECTABLE 2
> > > > > > +#define DPC_FATAL 4
> > > >
> > > > I think DPC_FATAL can be 3, since these values are not used as a bit
> > > > mask.
> > > >
> > > > > > struct pci_dev;
> > > > >
> > > > >
> > > > > Hi Bjorn,
> > > > >
> > > > >
> > > > > I have addressed all the comments, and I hope we are heading towards
> > > > > closure.
> > > > >
> > > > > I just figure that pcie_do_fatal_recovery (which is getting
> > > > > executed for
> > > > > DPC as well)
> > > > >
> > > > > if (result == PCI_ERS_RESULT_RECOVERED) {
> > > > > if (pcie_wait_for_link(udev, true))
> > > > > pci_rescan_bus(udev->bus);
> > > > > pci_info(dev, "Device recovery successful\n");
> > > > > }
> > > > >
> > > > > I have to correct it to
> > > > >
> > > > > if (service==AER && result == PCI_ERS_RESULT_RECOVERED) {
> > > > > if (pcie_wait_for_link(udev, true))
> > > > > pci_rescan_bus(udev->bus);
> > > > > pci_info(dev, "Device recovery successful\n");
> > > > > }
> > > >
> > > > This patch is mostly a restructuring of DPC and doesn't really change
> > > > its
> > > > behavior. DPC didn't previously call pcie_wait_for_link() or
> > > > pci_rescan_bus(), so I agree that adding the "service==AER" test will
> > > > help preserve the existing DPC behavior.
> > > >
> > > > However, the rescan should happen with DPC *somewhere* and we should
> > > > clarify where that is. Maybe for now we only need a comment about where
> > > > that happens. Ideally, we could eventually converge this so the same
> > > > mechanism is used for AER and DPC, so we wouldn't need a test like
> > > > "service=AER".
> >
> > Please still add a comment here about why the rescan behavior is
> > different.
> >
> > > I am sorry I pasted the wrong snippet.
> > > following needs to be fixed in v17.
> > > from:
> > > if (dev->hdr_type == PCI_HEADER_TYPE_BRIDGE) {
> > > /*
> > > * If the error is reported by a bridge, we think
> > > this error
> > > * is related to the downstream link of the bridge,
> > > so we
> > > * do error recovery on all subordinates of the bridge
> > > instead
> > > * of the bridge and clear the error status of the
> > > bridge.
> > > */
> > > pci_walk_bus(dev->subordinate, report_resume,
> > > &result_data);
> > > pci_cleanup_aer_uncorrect_error_status(dev);
> > > }
> > >
> > >
> > > to
> > >
> > > if (service==AER && dev->hdr_type == PCI_HEADER_TYPE_BRIDGE) {
> > > /*
> > > * If the error is reported by a bridge, we think
> > > this error
> > > * is related to the downstream link of the bridge,
> > > so we
> > > * do error recovery on all subordinates of the bridge
> > > instead
> > > * of the bridge and clear the error status of the
> > > bridge.
> > > */
> > > pci_walk_bus(dev->subordinate, report_resume,
> > > &result_data);
> > > pci_cleanup_aer_uncorrect_error_status(dev);
> > > }
> > >
> > > this is only needed in case of AER.
> >
> > Oh, I missed this before. It makes sense to clear the AER status
> > here, but why do we need to call report_resume()? We just called all
> > the driver .remove() methods and detached the drivers from the
> > devices. So I don't think report_resume() will do anything
> > ("dev->driver" should be NULL) except set the dev->error_state to
> > pci_channel_io_normal. We probably don't need that because we didn't
> > change error_state in this fatal error path.
>
> if you remember, the path ends up calling
> aer_error_resume
>
> the existing code ends up calling aer_error_resume as follows.
>
> 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)
>
> hence I think we have to call it in order to clear the root port
> PCI_ERR_UNCOR_STATUS and PCI_EXP_DEVSTA.
> makes sense ?

I know I sent you the call graph above, so you would think I might
understand it, but you would be mistaken :) This still doesn't make
sense to me.

I think your point is that we need to call aer_error_resume(). That
is the aerdriver.error_resume() method. The AER driver only binds to
root ports.

This path:

pcie_do_fatal_recovery
pci_walk_bus(dev->subordinate, report_resume, &result_data)

calls report_resume() for every device on the dev->subordinate bus
(and for anything below those devices). There are no root ports on
that dev->subordinate bus, because root ports are always on a root
bus, never on a subordinate bus.

So I don't see how report_resume() can ever get to aer_error_resume().
Can you instrument that path and verify that it actually does get
there somehow?