RE: [PATCH 4/6] Revert "PCI: hv: Fix a timing issue which causes kdump to fail occasionally"

[Dexuan Cui <decui@microsoft.com>]

> 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 The commit d6af2ed29c7c was originally made in July 2020 for RHEL 7.7,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 = 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 = 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",
> @@ -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 = true;
>  	int ret;
> 
>  	/*
> @@ -3633,47 +3666,11 @@ 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.
> -	 * 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 == -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;
> 
> --
> 2.25.1

+ Wei Hu.