Re: [PATCH 5.8 164/232] PCI: hv: Fix a timing issue which causes kdump to fail occasionally

[Greg Kroah-Hartman]

On Thu, Aug 20, 2020 at 03:48:23PM +0200, Greg Kroah-Hartman wrote:
> On Thu, Aug 20, 2020 at 09:29:24AM -0400, Sasha Levin wrote:
> > On Thu, Aug 20, 2020 at 01:00:51PM +0000, Michael Kelley wrote:
> > > From: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> Sent: Thursday, August 20, 2020 2:20 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(-)
> > > > 
> > > 
> > > This patch came through three days ago, and I indicated then that we don't want
> > > it backported to 5.8 and earlier.
> > 
> > Uh, I re-added it by mistake, sorry.
> 
> Ok, let me go drop it...

Oops, you already did :)