linux-kernel - RE: [Patch v2 1/2] PCI: hv: Fix a race condition when removing the device

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Message-ID: <MW2PR2101MB0892A9A0972199A2FF6D68B0BF459@MW2PR2101MB0892.namprd21.prod.outlook.com>
Date:   Fri, 23 Apr 2021 07:09:54 +0000
From:   Dexuan Cui <decui@...rosoft.com>
To:     "longli@...uxonhyperv.com" <longli@...uxonhyperv.com>,
        KY Srinivasan <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        Wei Liu <wei.liu@...nel.org>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Rob Herring <robh@...nel.org>,
        Bjorn Helgaas <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>
CC:     Long Li <longli@...rosoft.com>
Subject: RE: [Patch v2 1/2] PCI: hv: Fix a race condition when removing the
 device

> From: longli@...uxonhyperv.com <longli@...uxonhyperv.com>
> Sent: Wednesday, April 21, 2021 10:46 PM
> ...
> diff --git a/drivers/pci/controller/pci-hyperv.c
> b/drivers/pci/controller/pci-hyperv.c
> index 27a17a1e4a7c..fc948a2ed703 100644
> --- a/drivers/pci/controller/pci-hyperv.c
> +++ b/drivers/pci/controller/pci-hyperv.c
> @@ -444,7 +444,6 @@ enum hv_pcibus_state {
>  	hv_pcibus_probed,
>  	hv_pcibus_installed,
>  	hv_pcibus_removing,
> -	hv_pcibus_removed,
>  	hv_pcibus_maximum
>  };
> 
> @@ -3305,13 +3304,22 @@ static int hv_pci_remove(struct hv_device *hdev)
> 
>  	hbus = hv_get_drvdata(hdev);
>  	if (hbus->state == hv_pcibus_installed) {
> +		tasklet_disable(&hdev->channel->callback_event);
> +		hbus->state = hv_pcibus_removing;
> +		tasklet_enable(&hdev->channel->callback_event);
> +		destroy_workqueue(hbus->wq);

If we test "rmmod pci-hyperv", I suspect the warning will be printed:
hv_pci_remove() -> hv_pci_bus_exit() -> hv_pci_start_relations_work():

        if (hbus->state == hv_pcibus_removing) {
                dev_info(&hbus->hdev->device,
                         "PCI VMBus BUS_RELATIONS: ignored\n");
                return -ENOENT;
        }

Ideally we'd like to avoid the warning in the driver unloading case.

BTW, can you please add "hbus->wq = NULL;" after the line
"destroy_workqueue(hbus->wq);"? In case some other function could
still try to use hbus->wq by accident in the future, the error would be
easier to be understood.