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

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Date:   Thu, 20 Aug 2020 15:48:23 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Sasha Levin <sashal@...nel.org>
Cc:     Michael Kelley <mikelley@...rosoft.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>,
        Wei Hu <weh@...rosoft.com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>
Subject: Re: [PATCH 5.8 164/232] PCI: hv: Fix a timing issue which causes
 kdump to fail occasionally

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@...uxfoundation.org> Sent: Thursday, August 20, 2020 2:20 AM
> > > 
> > > From: Wei Hu <weh@...rosoft.com>
> > > 
> > > [ 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@microsoft.com/
> > > Fixes: c81992e7f4aa ("PCI: hv: Retry PCI bus D0 entry on invalid device state")
> > > Signed-off-by: Wei Hu <weh@...rosoft.com>
> > > [lorenzo.pieralisi@....com: fixed a comment and commit log]
> > > Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@....com>
> > > Reviewed-by: Michael Kelley <mikelley@...rosoft.com>
> > > Signed-off-by: Sasha Levin <sashal@...nel.org>
> > > ---
> > >  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...