RE: [PATCH v2 6/6] PCI: hv: Use async probing to reduce boot time

From: "Michael Kelley (LINUX)" <mikelley@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>,
	"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>,
	Saurabh Singh Sengar <ssengar@microsoft.com>,
	"helgaas@kernel.org" <helgaas@kernel.org>
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>,
	"stable@vger.kernel.org" <stable@vger.kernel.org>
Subject: RE: [PATCH v2 6/6] PCI: hv: Use async probing to reduce boot time
Date: Fri, 7 Apr 2023 16:11:31 +0000	[thread overview]
Message-ID: <BYAPR21MB168842E38534BD00CB1D27ABD7969@BYAPR21MB1688.namprd21.prod.outlook.com> (raw)
In-Reply-To: <20230404020545.32359-7-decui@microsoft.com>

From: Dexuan Cui <decui@microsoft.com> Sent: Monday, April 3, 2023 7:06 PM
> 
> Commit 414428c5da1c ("PCI: hv: Lock PCI bus on device eject") added
> pci_lock_rescan_remove() and pci_unlock_rescan_remove() in
> create_root_hv_pci_bus() and in hv_eject_device_work() to address the
> race between create_root_hv_pci_bus() and hv_eject_device_work(), but it
> turns that grubing the pci_rescan_remove_lock mutex is not enough:
> refer to the earlier fix "PCI: hv: Add a per-bus mutex state_lock".
> 
> Now with hbus->state_lock and other fixes, the race is resolved, so
> remove pci_{lock,unlock}_rescan_remove() in create_root_hv_pci_bus():
> this removes the serialization in hv_pci_probe() and hence allows
> async-probing (PROBE_PREFER_ASYNCHRONOUS) to work.
> 
> Add the async-probing flag to hv_pci_drv.
> 
> pci_{lock,unlock}_rescan_remove() in hv_eject_device_work() and in
> hv_pci_remove() are still kept: according to the comment before
> drivers/pci/probe.c: static DEFINE_MUTEX(pci_rescan_remove_lock),
> "PCI device removal routines should always be executed under this mutex".
> 
> Signed-off-by: Dexuan Cui <decui@microsoft.com>
> Cc: stable@vger.kernel.org
> ---
> 
> v2:
>   No change to the patch body.
>   Improved the commit message [Michael Kelley]
>   Added Cc:stable
> 
>  drivers/pci/controller/pci-hyperv.c | 11 +++++++++--
>  1 file changed, 9 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/pci/controller/pci-hyperv.c b/drivers/pci/controller/pci-hyperv.c
> index 3ae2f99dea8c2..2ea2b1b8a4c9a 100644
> --- a/drivers/pci/controller/pci-hyperv.c
> +++ b/drivers/pci/controller/pci-hyperv.c
> @@ -2312,12 +2312,16 @@ static int create_root_hv_pci_bus(struct
> hv_pcibus_device *hbus)
>  	if (error)
>  		return error;
> 
> -	pci_lock_rescan_remove();
> +	/*
> +	 * pci_lock_rescan_remove() and pci_unlock_rescan_remove() are
> +	 * unnecessary here, because we hold the hbus->state_lock, meaning
> +	 * hv_eject_device_work() and pci_devices_present_work() can't race
> +	 * with create_root_hv_pci_bus().
> +	 */
>  	hv_pci_assign_numa_node(hbus);
>  	pci_bus_assign_resources(bridge->bus);
>  	hv_pci_assign_slots(hbus);
>  	pci_bus_add_devices(bridge->bus);
> -	pci_unlock_rescan_remove();
>  	hbus->state = hv_pcibus_installed;
>  	return 0;
>  }
> @@ -4003,6 +4007,9 @@ static struct hv_driver hv_pci_drv = {
>  	.remove		= hv_pci_remove,
>  	.suspend	= hv_pci_suspend,
>  	.resume		= hv_pci_resume,
> +	.driver = {
> +		.probe_type = PROBE_PREFER_ASYNCHRONOUS,
> +	},
>  };
> 
>  static void __exit exit_hv_pci_drv(void)
> --
> 2.25.1

Reviewed-by: Michael Kelley <mikelley@microsoft.com>