Re: [PATCH 5.8 298/464] PCI: hv: Fix a timing issue which causes kdump to fail occasionally

[Sasha Levin]

On Mon, Aug 17, 2020 at 11:27:49PM +0000, Michael Kelley wrote:
> From: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>  Sent: Monday, August 17, 2020 8:14 AM
> > From: Wei Hu <weh@xxxxxxxxxxxxx>
> >
> > [ Upstream commit d6af2ed29c7c1c311b96dac989dcb991e90ee195 ]
> >
> > Kdump could fail sometime on Hyper-V guest because the retry in
> > hv_pci_enter_d0() releases child device structures in hv_pci_bus_exit().
> >
> > Although there is a second asynchronous device relations message sending
> > from the host, if this message arrives to the guest after
> > hv_send_resource_allocated() is called, the retry would fail.
> >
> > Fix the problem by moving retry to hv_pci_probe() and start the retry
> > from hv_pci_query_relations() call.  This will cause a device relations
> > message to arrive to the guest synchronously; the guest would then be
> > able to rebuild the child device structures before calling
> > hv_send_resource_allocated().
> >
> > Link:
> > https://lore.kernel.org/linux-hyperv/20200727071731.18516-1-weh@xxxxxxxxxxxxx/
> > Fixes: c81992e7f4aa ("PCI: hv: Retry PCI bus D0 entry on invalid device state")
> > Signed-off-by: Wei Hu <weh@xxxxxxxxxxxxx>
> > [lorenzo.pieralisi@xxxxxxx: fixed a comment and commit log]
> > Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@xxxxxxx>
> > Reviewed-by: Michael Kelley <mikelley@xxxxxxxxxxxxx>
> > Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
> > ---
> >  drivers/pci/controller/pci-hyperv.c | 71 +++++++++++++++--------------
> >  1 file changed, 37 insertions(+), 34 deletions(-)
>
> Greg --
>
> Don't backport this patch to 5.8 and earlier.  It doesn't break anything,
> but it doesn't fully accomplish what was intended either.  As such it will
> probably need a revision in 5.9.  Wei Hu is unavailable for a few days
> for personal reasons, so I'm jumping in here on his behalf.

I've dropped it, will wait for the fix.

--
Thanks,
Sasha