linux-kernel - RE: [PATCH v2 1/6] PCI: hv: Fix a race condition bug in hv_pci_query

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Message-ID: <BYAPR21MB16883C7A762A013B791B6091D7969@BYAPR21MB1688.namprd21.prod.outlook.com>
Date:   Fri, 7 Apr 2023 16:03:57 +0000
From:   "Michael Kelley (LINUX)" <mikelley@...rosoft.com>
To:     Dexuan Cui <decui@...rosoft.com>,
        "bhelgaas@...gle.com" <bhelgaas@...gle.com>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "edumazet@...gle.com" <edumazet@...gle.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Jake Oshins <jakeo@...rosoft.com>,
        "kuba@...nel.org" <kuba@...nel.org>, "kw@...ux.com" <kw@...ux.com>,
        KY Srinivasan <kys@...rosoft.com>,
        "leon@...nel.org" <leon@...nel.org>,
        "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
        "lpieralisi@...nel.org" <lpieralisi@...nel.org>,
        "pabeni@...hat.com" <pabeni@...hat.com>,
        "robh@...nel.org" <robh@...nel.org>,
        "saeedm@...dia.com" <saeedm@...dia.com>,
        "wei.liu@...nel.org" <wei.liu@...nel.org>,
        Long Li <longli@...rosoft.com>,
        "boqun.feng@...il.com" <boqun.feng@...il.com>,
        Saurabh Singh Sengar <ssengar@...rosoft.com>,
        "helgaas@...nel.org" <helgaas@...nel.org>
CC:     "linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-rdma@...r.kernel.org" <linux-rdma@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>
Subject: RE: [PATCH v2 1/6] PCI: hv: Fix a race condition bug in
 hv_pci_query_relations()

From: Dexuan Cui <decui@...rosoft.com> Sent: Monday, April 3, 2023 7:06 PM
> 
> Fix the longstanding race between hv_pci_query_relations() and
> survey_child_resources() by flushing the workqueue before we exit from
> hv_pci_query_relations().
> 
> Fixes: 4daace0d8ce8 ("PCI: hv: Add paravirtual PCI front-end for Microsoft Hyper-V
> VMs")
> Signed-off-by: Dexuan Cui <decui@...rosoft.com>
> Cc: stable@...r.kernel.org
> ---
> 
> v2:
>   Removed the "debug code".
>   No change to the patch body.
>   Added Cc:stable
> 
>  drivers/pci/controller/pci-hyperv.c | 13 +++++++++++++
>  1 file changed, 13 insertions(+)
> 
> diff --git a/drivers/pci/controller/pci-hyperv.c b/drivers/pci/controller/pci-hyperv.c
> index f33370b756283..b82c7cde19e66 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 = wait_for_response(hdev, &comp);
> 
> +	/*
> +	 * 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);
> +
>  	return ret;
>  }
> 
> --
> 2.25.1

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