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Date: Wed, 8 Apr 2020 16:15:20 +1000
From: Sam Bobroff <sbobroff@linux.ibm.com>
To: "Oliver O'Halloran" <oohall@gmail.com>
Subject: Re: [PATCH 2/4] powerpc/eeh: Release EEH device state synchronously
References: <cover.1585544197.git.sbobroff@linux.ibm.com>
 <6b3ce475194cd3c1aefd876e311b5a218c3a627a.1585544197.git.sbobroff@linux.ibm.com>
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On Fri, Apr 03, 2020 at 03:51:18PM +1100, Oliver O'Halloran wrote:
> On Mon, 2020-03-30 at 15:56 +1100, Sam Bobroff wrote:
> > EEH device state is currently removed (by eeh_remove_device()) during
> > the device release handler, which is invoked as the device's reference
> > count drops to zero. This may take some time, or forever, as other
> > threads may hold references.
> >=20
> > However, the PCI device state is released synchronously by
> > pci_stop_and_remove_bus_device(). This mismatch causes problems, for
> > example the device may be re-discovered as a new device before the
> > release handler has been called, leaving the PCI and EEH state
> > mismatched.
> >=20
> > So instead, call eeh_remove_device() from the bus device removal
> > handlers, which are called synchronously in the removal path.
> >=20
> > Signed-off-by: Sam Bobroff <sbobroff@linux.ibm.com>
> > ---
> >  arch/powerpc/kernel/eeh.c         | 26 ++++++++++++++++++++++++++
> >  arch/powerpc/kernel/pci-hotplug.c |  2 --
> >  2 files changed, 26 insertions(+), 2 deletions(-)
> >=20
> > diff --git a/arch/powerpc/kernel/eeh.c b/arch/powerpc/kernel/eeh.c
> > index 17cb3e9b5697..c36c5a7db5ca 100644
> > --- a/arch/powerpc/kernel/eeh.c
> > +++ b/arch/powerpc/kernel/eeh.c
> > @@ -1106,6 +1106,32 @@ static int eeh_init(void)
> > =20
> >  core_initcall_sync(eeh_init);
> > =20
> > +static int eeh_device_notifier(struct notifier_block *nb,
> > +			       unsigned long action, void *data)
> > +{
> > +	struct device *dev =3D data;
> > +
> > +	switch (action) {
> > +	case BUS_NOTIFY_DEL_DEVICE:
> > +		eeh_remove_device(to_pci_dev(dev));
> > +		break;
> > +	default:
> > +		break;
> > +	}
>=20
> A comment briefly explaining why we're not doing anything in the add
> case might be nice.

Good point, I'll add something for v2.
>=20
> Reviewed-by: Oliver O'Halloran <oohall@gmail.com>
>=20
> > +	return NOTIFY_DONE;
> > +}
> > +
> > +static struct notifier_block eeh_device_nb =3D {
> > +	.notifier_call =3D eeh_device_notifier,
> > +};
> > +
> > +static __init int eeh_set_bus_notifier(void)
> > +{
> > +	bus_register_notifier(&pci_bus_type, &eeh_device_nb);
> > +	return 0;
> > +}
> > +arch_initcall(eeh_set_bus_notifier);
> > +
> >  /**
> >   * eeh_add_device_early - Enable EEH for the indicated device node
> >   * @pdn: PCI device node for which to set up EEH
> > diff --git a/arch/powerpc/kernel/pci-hotplug.c b/arch/powerpc/kernel/pc=
i-hotplug.c
> > index d6a67f814983..28e9aa274f64 100644
> > --- a/arch/powerpc/kernel/pci-hotplug.c
> > +++ b/arch/powerpc/kernel/pci-hotplug.c
> > @@ -57,8 +57,6 @@ void pcibios_release_device(struct pci_dev *dev)
> >  	struct pci_controller *phb =3D pci_bus_to_host(dev->bus);
> >  	struct pci_dn *pdn =3D pci_get_pdn(dev);
> > =20
> > -	eeh_remove_device(dev);
> > -
> >  	if (phb->controller_ops.release_device)
> >  		phb->controller_ops.release_device(dev);
> > =20
>=20

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