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

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Message-ID: <20180509130730.GA236548@bhelgaas-glaptop.roam.corp.google.com>
Date:   Wed, 9 May 2018 08:07:30 -0500
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Oza Pawandeep <poza@...eaurora.org>
Cc:     Bjorn Helgaas <bhelgaas@...gle.com>,
        Philippe Ombredanne <pombredanne@...b.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Kate Stewart <kstewart@...uxfoundation.org>,
        linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
        Dongdong Liu <liudongdong3@...wei.com>,
        Keith Busch <keith.busch@...el.com>, Wei Zhang <wzhang@...com>,
        Sinan Kaya <okaya@...eaurora.org>,
        Timur Tabi <timur@...eaurora.org>
Subject: Re: [PATCH v15 3/9] PCI/AER: Handle ERR_FATAL with removal and
 re-enumeration of devices

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@...eaurora.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.