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Subject: RE: [PATCH 1/6] PCI: hv: fix a race condition bug in
 hv_pci_query_relations()
Thread-Topic: [PATCH 1/6] PCI: hv: fix a race condition bug in
 hv_pci_query_relations()
Thread-Index: AQHZYTEw5EIgYDC+IUOtVNpvTo0Kxa8QZ0BA
Date:   Tue, 28 Mar 2023 16:48:44 +0000
Message-ID: <PH7PR21MB32632E889A7F589C32FE51EDCE889@PH7PR21MB3263.namprd21.prod.outlook.com>
References: <20230328045122.25850-1-decui@microsoft.com>
 <20230328045122.25850-2-decui@microsoft.com>
In-Reply-To: <20230328045122.25850-2-decui@microsoft.com>
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=20
> diff --git a/drivers/pci/controller/pci-hyperv.c b/drivers/pci/controller=
/pci-
> hyperv.c
> index f33370b75628..b82c7cde19e6 100644
> --- a/drivers/pci/controller/pci-hyperv.c
> +++ b/drivers/pci/controller/pci-hyperv.c
> @@ -3308,6 +3308,19 @@ static int hv_pci_query_relations(struct hv_device
> *hdev)
>  	if (!ret)
>  		ret =3D wait_for_response(hdev, &comp);
>=20
> +	/*
> +	 * In the case of fast device addition/removal, it's possible that
> +	 * vmbus_sendpacket() or wait_for_response() returns -ENODEV but
> we
> +	 * already got a PCI_BUS_RELATIONS* message from the host and the
> +	 * channel callback already scheduled a work to hbus->wq, which can
> be
> +	 * running survey_child_resources() -> complete(&hbus-
> >survey_event),
> +	 * even after hv_pci_query_relations() exits and the stack variable
> +	 * 'comp' is no longer valid. This can cause a strange hang issue
> +	 * or sometimes a page fault. Flush hbus->wq before we exit from
> +	 * hv_pci_query_relations() to avoid the issues.
> +	 */
> +	flush_workqueue(hbus->wq);

Is it possible for PCI_BUS_RELATIONS to be scheduled arrive after calling f=
lush_workqueue(hbus->wq)?

> +
>  	return ret;
>  }
>=20
> --
> 2.25.1