linux-kernel - Re: [PATCH 0/5] s390/pci: automatic error recovery

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Date:   Tue, 7 Sep 2021 12:04:35 +1000
From:   "Oliver O'Halloran" <oohall@...il.com>
To:     Niklas Schnelle <schnelle@...ux.ibm.com>
Cc:     Bjorn Helgaas <bhelgaas@...gle.com>,
        Linas Vepstas <linasvepstas@...il.com>,
        Russell Currey <ruscur@...sell.cc>,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-s390@...r.kernel.org,
        Matthew Rosato <mjrosato@...ux.ibm.com>,
        Pierre Morel <pmorel@...ux.ibm.com>
Subject: Re: [PATCH 0/5] s390/pci: automatic error recovery

On Mon, Sep 6, 2021 at 7:49 PM Niklas Schnelle <schnelle@...ux.ibm.com> wrote:
>
> Patch 3 I already sent separately resulting in the discussion below but without
> a final conclusion.
>
> https://lore.kernel.org/lkml/20210720150145.640727-1-schnelle@linux.ibm.com/
>
> I believe even though there were some doubts about the use of
> pci_dev_is_added() by arch code the existing uses as well as the use in the
> final patch of this series warrant this export.

The use of pci_dev_is_added() in arch/powerpc was because in the past
pci_bus_add_device() could be called before pci_device_add(). That was
fixed a while ago so It should be safe to remove those calls now.

> Patch 4 "PCI: Export pci_dev_lock()" is basically an extension to commit
> e3a9b1212b9d ("PCI: Export pci_dev_trylock() and pci_dev_unlock()") which
> already exported pci_dev_trylock(). In the final patch we make use of
> pci_dev_lock() to wait for any other exclusive uses of the pdev to be finished
> before starting recovery.

Hmm, I noticed the EEH
(arch/powerpc/kernel/eeh_driver.c:eeh_pe_report_edev())  and the
generic PCIe error recovery code (see
drivers/pci/pcie/err.c:report_error_detected()) only call
device_lock() before entering the driver's error handling callbacks. I
wonder if they should be using pci_dev_lock() instead. The only real
difference is that pci_dev_lock() will also block user space from
accessing the device's config space while error recovery is in
progress which seems sensible enough.