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Message-ID: <SG2P153MB03774814C5D6450238CC4471BB760@SG2P153MB0377.APCP153.PROD.OUTLOOK.COM>
Date: Thu, 23 Jul 2020 15:52:39 +0000
From: Wei Hu <weh@...rosoft.com>
To: Lorenzo Pieralisi <lorenzo.pieralisi@....com>
CC: KY Srinivasan <kys@...rosoft.com>,
Haiyang Zhang <haiyangz@...rosoft.com>,
Stephen Hemminger <sthemmin@...rosoft.com>,
"wei.liu@...nel.org" <wei.liu@...nel.org>,
"robh@...nel.org" <robh@...nel.org>,
"bhelgaas@...gle.com" <bhelgaas@...gle.com>,
"linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>,
"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
Dexuan Cui <decui@...rosoft.com>,
Michael Kelley <mikelley@...rosoft.com>
Subject: RE: [PATCH v3] PCI: hv: Fix a timing issue which causes kdump to fail
occasionally
> -----Original Message-----
> From: Lorenzo Pieralisi <lorenzo.pieralisi@....com>
> > Kdump could fail sometime on Hyper-V guest over Accelerated Network
> > interface. This is because the retry in hv_pci_enter_d0() relies on an
> > asynchronous host event arriving before the guest calls
> > hv_send_resources_allocated(). Fix the problem by moving retry to
> > hv_pci_probe(), removing this dependency and making the calling
> > sequence synchronous.
>
> You have to explain why this code move fixes the problem
How about following commit message:
Kdump could fail sometime on Hyper-V guest over Accelerated Network
nterface. This is because the retry in hv_pci_enter_d0() relies on an
asynchronous host event arriving before the guest calls
hv_send_resources_allocated(). Fix the problem by moving retry to
hv_pci_probe() and start the retry from hv_pci_query_relations() call.
This causes the host to generate an synchronous event, hence removing
this unreliable dependency.
> and you also have to
> add a comment to the code so that anyone who has to fix it in the future can
> understand why the code is where you are moving it to and why that's a
> solution.
It already has the comment in the code as:
+ * The retry should start from hv_pci_query_relations() call.
It would be a bug if the retry does not start from this according to the host
Behaviour. So I think no further explanation would be needed.
>
> > Fixes: c81992e7f4aa ("PCI: hv: Retry PCI bus D0 entry on invalid
> > device state")
> > Signed-off-by: Wei Hu <weh@...rosoft.com>
>
> Please carry tags and send patches -in-reply-to the previous version to allow
> threading.
>
Do you mean to add review-by tags? If not would you please elaborate what
'carry tags' means? Sorry I am not familiar to this term.
Thanks,
Wei
> Thanks,
> Lorenzo
>
> > ---
> > v2: Adding Fixes tag according to Michael Kelley's review comment.
> > v3: Fix couple typos and reword commit message to make it clearer.
> > Thanks the comments from Bjorn Helgaas.
> >
> > drivers/pci/controller/pci-hyperv.c | 66
> > ++++++++++++++---------------
> > 1 file changed, 32 insertions(+), 34 deletions(-)
> >
> > diff --git a/drivers/pci/controller/pci-hyperv.c
> > b/drivers/pci/controller/pci-hyperv.c
> > index bf40ff09c99d..738ee30f3334 100644
> > --- a/drivers/pci/controller/pci-hyperv.c
> > +++ b/drivers/pci/controller/pci-hyperv.c
> > @@ -2759,10 +2759,8 @@ 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 = 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 @@
> > -2789,38 +2787,6 @@ 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 = 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 = 255;
> > -
> > - ret = hv_pci_bus_exit(hdev, true);
> > -
> > - if (ret == 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", @@
> > -3058,6 +3024,7 @@ static int hv_pci_probe(struct hv_device *hdev,
> > struct hv_pcibus_device *hbus;
> > u16 dom_req, dom;
> > char *name;
> > + bool enter_d0_retry = true;
> > int ret;
> >
> > /*
> > @@ -3178,11 +3145,42 @@ static int hv_pci_probe(struct hv_device *hdev,
> > if (ret)
> > goto free_fwnode;
> >
> > +retry:
> > ret = hv_pci_query_relations(hdev);
> > if (ret)
> > goto free_irq_domain;
> >
> > ret = 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.
> > + * The retry should start from hv_pci_query_relations() call.
> > + */
> > + if (ret == -EPROTO && enter_d0_retry) {
> > + enter_d0_retry = 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 = 255;
> > + ret = hv_pci_bus_exit(hdev, true);
> > +
> > + if (ret == 0)
> > + goto retry;
> > +
> > + dev_err(&hdev->device,
> > + "Retrying D0 failed with ret %d\n", ret);
> > + }
> > if (ret)
> > goto free_irq_domain;
> >
> > --
> > 2.20.1
> >
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