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From:   Wei Hu <weh@microsoft.com>
To:     Dexuan Cui <decui@microsoft.com>,
        "bhelgaas@google.com" <bhelgaas@google.com>,
        "davem@davemloft.net" <davem@davemloft.net>,
        "edumazet@google.com" <edumazet@google.com>,
        Haiyang Zhang <haiyangz@microsoft.com>,
        Jake Oshins <jakeo@microsoft.com>,
        "kuba@kernel.org" <kuba@kernel.org>, "kw@linux.com" <kw@linux.com>,
        KY Srinivasan <kys@microsoft.com>,
        "leon@kernel.org" <leon@kernel.org>,
        "linux-pci@vger.kernel.org" <linux-pci@vger.kernel.org>,
        "lpieralisi@kernel.org" <lpieralisi@kernel.org>,
        "Michael Kelley (LINUX)" <mikelley@microsoft.com>,
        "pabeni@redhat.com" <pabeni@redhat.com>,
        "robh@kernel.org" <robh@kernel.org>,
        "saeedm@nvidia.com" <saeedm@nvidia.com>,
        "wei.liu@kernel.org" <wei.liu@kernel.org>,
        Long Li <longli@microsoft.com>,
        "boqun.feng@gmail.com" <boqun.feng@gmail.com>
CC:     "linux-hyperv@vger.kernel.org" <linux-hyperv@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "linux-rdma@vger.kernel.org" <linux-rdma@vger.kernel.org>,
        "netdev@vger.kernel.org" <netdev@vger.kernel.org>
Subject: RE: [PATCH 4/6] Revert "PCI: hv: Fix a timing issue which causes
 kdump to fail occasionally"
Thread-Topic: [PATCH 4/6] Revert "PCI: hv: Fix a timing issue which causes
 kdump to fail occasionally"
Thread-Index: AQHZYTE02QJw3cJyrE2OQ7EX2SDB268Pu6LwgAMPN3A=
Date:   Thu, 30 Mar 2023 05:17:04 +0000
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> -----Original Message-----
> From: Dexuan Cui <decui@microsoft.com>
> Sent: Tuesday, March 28, 2023 2:33 PM
> To: bhelgaas@google.com; davem@davemloft.net; edumazet@google.com;
> Haiyang Zhang <haiyangz@microsoft.com>; Jake Oshins
> <jakeo@microsoft.com>; kuba@kernel.org; kw@linux.com; KY Srinivasan
> <kys@microsoft.com>; leon@kernel.org; linux-pci@vger.kernel.org;
> lpieralisi@kernel.org; Michael Kelley (LINUX) <mikelley@microsoft.com>;
> pabeni@redhat.com; robh@kernel.org; saeedm@nvidia.com;
> wei.liu@kernel.org; Long Li <longli@microsoft.com>; boqun.feng@gmail.com;
> Wei Hu <weh@microsoft.com>
> Cc: linux-hyperv@vger.kernel.org; linux-kernel@vger.kernel.org; linux-
> rdma@vger.kernel.org; netdev@vger.kernel.org
> Subject: RE: [PATCH 4/6] Revert "PCI: hv: Fix a timing issue which causes
> kdump to fail occasionally"
>=20
> > From: Dexuan Cui <decui@microsoft.com>
> > Sent: Monday, March 27, 2023 9:51 PM
> > To: bhelgaas@google.com; davem@davemloft.net; Dexuan Cui
> > <decui@microsoft.com>; edumazet@google.com; Haiyang Zhang
> > <haiyangz@microsoft.com>; Jake Oshins <jakeo@microsoft.com>;
> > kuba@kernel.org; kw@linux.com; KY Srinivasan <kys@microsoft.com>;
> > leon@kernel.org; linux-pci@vger.kernel.org; lpieralisi@kernel.org;
> > Michael Kelley (LINUX) <mikelley@microsoft.com>; pabeni@redhat.com;
> > robh@kernel.org; saeedm@nvidia.com; wei.liu@kernel.org; Long Li
> > <longli@microsoft.com>; boqun.feng@gmail.com
> > Cc: linux-hyperv@vger.kernel.org; linux-kernel@vger.kernel.org;
> > linux-rdma@vger.kernel.org; netdev@vger.kernel.org
> > Subject: [PATCH 4/6] Revert "PCI: hv: Fix a timing issue which causes
> > kdump to fail occasionally"
> >
> > This reverts commit d6af2ed29c7c1c311b96dac989dcb991e90ee195.
> >
> > The statement "the hv_pci_bus_exit() call releases structures of all
> > its child devices" in commit d6af2ed29c7c is not true: in the path
> > hv_pci_probe() -> hv_pci_enter_d0() -> hv_pci_bus_exit(hdev, true):
> > the parameter "keep_devs" is true, so hv_pci_bus_exit() does *not*
> > release the child "struct hv_pci_dev *hpdev" that is created earlier
> > in
> > pci_devices_present_work() -> new_pcichild_device().
> >
> > The commit d6af2ed29c7c was originally made in July 2020 for RHEL 7.7,
> > where the old version of hv_pci_bus_exit() was used; when the commit
> > was rebased and merged into the upstream, people didn't notice that
> > it's not really necessary. The commit itself doesn't cause any issue,
> > but it makes hv_pci_probe() more complicated. Revert it to facilitate
> > some upcoming changes to hv_pci_probe().
> >
> > Signed-off-by: Dexuan Cui <decui@microsoft.com>
> > ---
> >  drivers/pci/controller/pci-hyperv.c | 71
> > ++++++++++++++---------------
> >  1 file changed, 34 insertions(+), 37 deletions(-)
> >
> > diff --git a/drivers/pci/controller/pci-hyperv.c
> > b/drivers/pci/controller/pci-hyperv.c
> > index 46df6d093d68..48feab095a14 100644
> > --- a/drivers/pci/controller/pci-hyperv.c
> > +++ b/drivers/pci/controller/pci-hyperv.c
> > @@ -3225,8 +3225,10 @@ static int hv_pci_enter_d0(struct hv_device
> *hdev)
> >  	struct pci_bus_d0_entry *d0_entry;
> >  	struct hv_pci_compl comp_pkt;
> >  	struct pci_packet *pkt;
> > +	bool retry =3D true;
> >  	int ret;
> >
> > +enter_d0_retry:
> >  	/*
> >  	 * Tell the host that the bus is ready to use, and moved into the
> >  	 * powered-on state.  This includes telling the host which region @@
> > -3253,6 +3255,38 @@ static int hv_pci_enter_d0(struct hv_device *hdev)
> >  	if (ret)
> >  		goto exit;
> >
> > +	/*
> > +	 * In certain case (Kdump) the pci device of interest was
> > +	 * not cleanly shut down and resource is still held on host
> > +	 * side, the host could return invalid device status.
> > +	 * We need to explicitly request host to release the resource
> > +	 * and try to enter D0 again.
> > +	 */
> > +	if (comp_pkt.completion_status < 0 && retry) {
> > +		retry =3D false;
> > +
> > +		dev_err(&hdev->device, "Retrying D0 Entry\n");
> > +
> > +		/*
> > +		 * Hv_pci_bus_exit() calls hv_send_resource_released()
> > +		 * to free up resources of its child devices.
> > +		 * In the kdump kernel we need to set the
> > +		 * wslot_res_allocated to 255 so it scans all child
> > +		 * devices to release resources allocated in the
> > +		 * normal kernel before panic happened.
> > +		 */
> > +		hbus->wslot_res_allocated =3D 255;
> > +
> > +		ret =3D hv_pci_bus_exit(hdev, true);
> > +
> > +		if (ret =3D=3D 0) {
> > +			kfree(pkt);
> > +			goto enter_d0_retry;
> > +		}
> > +		dev_err(&hdev->device,
> > +			"Retrying D0 failed with ret %d\n", ret);
> > +	}
> > +
> >  	if (comp_pkt.completion_status < 0) {
> >  		dev_err(&hdev->device,
> >  			"PCI Pass-through VSP failed D0 Entry with
> status %x\n", @@
> > -3493,7 +3527,6 @@ static int hv_pci_probe(struct hv_device *hdev,
> >  	struct hv_pcibus_device *hbus;
> >  	u16 dom_req, dom;
> >  	char *name;
> > -	bool enter_d0_retry =3D true;
> >  	int ret;
> >
> >  	/*
> > @@ -3633,47 +3666,11 @@ static int hv_pci_probe(struct hv_device *hdev,
> >  	if (ret)
> >  		goto free_fwnode;
> >
> > -retry:
> >  	ret =3D hv_pci_query_relations(hdev);
> >  	if (ret)
> >  		goto free_irq_domain;
> >
> >  	ret =3D hv_pci_enter_d0(hdev);
> > -	/*
> > -	 * In certain case (Kdump) the pci device of interest was
> > -	 * not cleanly shut down and resource is still held on host
> > -	 * side, the host could return invalid device status.
> > -	 * We need to explicitly request host to release the resource
> > -	 * and try to enter D0 again.
> > -	 * Since the hv_pci_bus_exit() call releases structures
> > -	 * of all its child devices, we need to start the retry from
> > -	 * hv_pci_query_relations() call, requesting host to send
> > -	 * the synchronous child device relations message before this
> > -	 * information is needed in hv_send_resources_allocated()
> > -	 * call later.
> > -	 */
> > -	if (ret =3D=3D -EPROTO && enter_d0_retry) {
> > -		enter_d0_retry =3D false;
> > -
> > -		dev_err(&hdev->device, "Retrying D0 Entry\n");
> > -
> > -		/*
> > -		 * Hv_pci_bus_exit() calls hv_send_resources_released()
> > -		 * to free up resources of its child devices.
> > -		 * In the kdump kernel we need to set the
> > -		 * wslot_res_allocated to 255 so it scans all child
> > -		 * devices to release resources allocated in the
> > -		 * normal kernel before panic happened.
> > -		 */
> > -		hbus->wslot_res_allocated =3D 255;
> > -		ret =3D hv_pci_bus_exit(hdev, true);
> > -
> > -		if (ret =3D=3D 0)
> > -			goto retry;
> > -
> > -		dev_err(&hdev->device,
> > -			"Retrying D0 failed with ret %d\n", ret);
> > -	}
> >  	if (ret)
> >  		goto free_irq_domain;
> >
> > --
> > 2.25.1
>

Acked-by: Wei Hu <weh@microsoft.com>