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Date:   Thu, 10 May 2018 14:15:10 +0100
From:   okaya@codeaurora.org
To:     Bjorn Helgaas <helgaas@kernel.org>
Cc:     poza@codeaurora.org, Bjorn Helgaas <bhelgaas@google.com>,
        Philippe Ombredanne <pombredanne@nexb.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Kate Stewart <kstewart@linuxfoundation.org>,
        linux-pci@vger.kernel.org, linux-kernel@vger.kernel.org,
        Dongdong Liu <liudongdong3@huawei.com>,
        Keith Busch <keith.busch@intel.com>, Wei Zhang <wzhang@fb.com>,
        Timur Tabi <timur@codeaurora.org>,
        linux-pci-owner@vger.kernel.org
Subject: Re: [PATCH v15 3/9] PCI/AER: Handle ERR_FATAL with removal and
 re-enumeration of devices
In-Reply-To: <20180510131027.GB173327@bhelgaas-glaptop.roam.corp.google.com>
References: <1525323838-1735-1-git-send-email-poza@codeaurora.org>
 <1525323838-1735-4-git-send-email-poza@codeaurora.org>
 <20180508235330.GN161390@bhelgaas-glaptop.roam.corp.google.com>
 <20180509130730.GA236548@bhelgaas-glaptop.roam.corp.google.com>
 <b1f9aaf43300ef7a829001e964bf4e72@codeaurora.org>
 <20180509232111.GA43216@bhelgaas-glaptop.roam.corp.google.com>
 <c2238d174e550250b0b93a497c40cf6a@codeaurora.org>
 <20180510131027.GB173327@bhelgaas-glaptop.roam.corp.google.com>
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On 2018-05-10 14:10, Bjorn Helgaas wrote:
> 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);

Why are we calling resume?

>>                 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.
>> 
>>