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From: "Oliver O'Halloran" <oohall@gmail.com>
Date: Wed, 20 Nov 2019 00:22:18 +1100
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Subject: Re: [PATCH 02/11] powerpc/powernv/ioda: Protect PE list
To: Frederic Barrat <fbarrat@linux.ibm.com>
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On Tue, Nov 19, 2019 at 11:57 PM Frederic Barrat <fbarrat@linux.ibm.com> wrote:
>
> > Do the other accessors of ioda.pe_list also need mutex protection?
> > pnv_ioda_setup_bus_PE()
> > pnv_pci_dma_bus_setup()
> > pnv_pci_init_ioda_phb()
> > pnv_pci_ioda_setup_PEs()
>
>
> I think we could also use it there, it wouldn't hurt. Those functions
> are called when the kernel is building part of the PCI topology, and
> devices are not really active yet, so I don't think it's absolutely
> required.
>
> I'm actually not sure my patch is needed either. With hotplug, the
> devices can come and go, whereas the PHB remains. So it feels right to
> start protecting the list when adding/removing a device. But I don't
> think we can really have concurrency and have 2 different operations
> adding/removing devices at the same time under the same PHB, at least
> for opencapi. Maybe for PCI, if we have multiple slots under the same
> PHB. Not sure.

Creation of new pci_dev's is serialised by the global pci rescan and
remove lock so on the creation side it's not an issue. However, we can
release IODA PEs in the pci_dev's release function which might be
called without that lock held. It's pretty hard to hit that case
though since it require something to be holding a ref to the pci_dev
even after the driver's ->remove() function has been called.