linux-kernel - Re: [PATCH v2 1/6] PCI/AER: Take severity mask into account while clearing error bits

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Date:   Tue, 17 Jul 2018 16:36:01 -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 v2 1/6] PCI/AER: Take severity mask into account while
 clearing error bits

On Tue, Jul 17, 2018 at 02:03:29PM -0500, Bjorn Helgaas wrote:
> Hi Oza,
> 
> Thanks for doing this!
> 
> On Fri, Jun 22, 2018 at 05:58:09AM -0400, Oza Pawandeep wrote:
> > pci_cleanup_aer_uncorrect_error_status() is called by different slot_reset
> > callbacks in case of ERR_NONFATAL.
> 
> IIRC, the current strategy is:
> 
>   ERR_COR: log only
>   ERR_NONFATAL: call driver callbacks (pci_error_handlers)
>   ERR_FATAL: remove device and re-enumerate
> 
> So these slot_reset callbacks are only used for ERR_NONFATAL, which
> are all uncorrectable errors, of course.
> 
> This patch makes it so that when the slot_reset callbacks call
> pci_cleanup_aer_uncorrect_error_status(), we only clear the
> bits set by ERR_NONFATAL events (this is determined by
> PCI_ERR_UNCOR_SEVER).
> 
> That makes good sense to me.  All these status bits are RW1CS, so they
> will be preserved across a reset but will be cleared when we
> re-enumerate, in this path:
> 
>   pci_init_capabilities
>     pci_aer_init
>       pci_cleanup_aer_error_status_regs
>       # clear all PCI_ERR_UNCOR_STATUS and PCI_ERR_COR_STATUS bits
> 
> > AER uncorrectable error status should take severity into account in order
> > to clear the bits, so that ERR_NONFATAL path does not clear the bit which
> > are marked with severity fatal.
> 
> Two comments:
> 
> 1) Can you split this into two patches, one that changes
> pci_cleanup_aer_uncorrect_error_status() so it looks like the error
> clearing code in aer_error_resume(), and a second that factors out the
> duplicate code?
> 
> 2) Maybe use "sev" or "sever" instead of "mask" for the local
> variable, since there is also a separate PCI_ERR_UNCOR_MASK register,
> which is not involved here.

Let me back up a little here: I'm not asking you to do the things
below here.  They're just possible future things, so we can think
about them after this series.  And the things above are things I can
easily do myself.  So no action required from you, unless you think
I'm on the wrong track :)

> 3) The "pci_cleanup_aer_uncorrect_error_status()" name no longer
> really describes what this does.  Something like
> "pci_aer_clear_nonfatal_status()" would be more descriptive.  But I
> see you have a subsequent patch (which I haven't looked at yet) that
> is related to this.
> 
> 4) I don't think the driver slot_reset callbacks should be responsible
> for clearing these AER status bits.  Can we clear them somewhere in
> the pcie_do_nonfatal_recovery() path and remove these calls from the
> drivers?
> 
> 5) In principle, we should only read PCI_ERR_UNCOR_STATUS *once* per
> device when handling an error.  We currently read it three times:
> 
>   aer_isr
>     aer_isr_one_error
>       find_source_device
>         find_device_iter
>           is_error_source
>             read PCI_ERR_UNCOR_STATUS              # 1
>       aer_process_err_devices
>         get_device_error_info(e_info->dev[i])
>           read PCI_ERR_UNCOR_STATUS                # 2
>         handle_error_source
>           pcie_do_nonfatal_recovery
>             ...
>               report_slot_reset
>                 driver->err_handler->slot_reset
>                   pci_cleanup_aer_uncorrect_error_status
>                     read PCI_ERR_UNCOR_STATUS      # 3
> 
> OK, that was more than two comments :)