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From:   Michael Kelley <mikelley@microsoft.com>
To:     Dexuan Cui <decui@microsoft.com>,
        "wei.liu@kernel.org" <wei.liu@kernel.org>,
        KY Srinivasan <kys@microsoft.com>,
        Haiyang Zhang <haiyangz@microsoft.com>,
        Stephen Hemminger <sthemmin@microsoft.com>,
        "linux-hyperv@vger.kernel.org" <linux-hyperv@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        vkuznets <vkuznets@redhat.com>
Subject: RE: [PATCH] Drivers: hv: vmbus: hibernation: do not hang forever in
 vmbus_bus_resume()
Thread-Topic: [PATCH] Drivers: hv: vmbus: hibernation: do not hang forever in
 vmbus_bus_resume()
Thread-Index: AQHWgzAke73uaFTcbE6462qO1rlMYalfQJjw
Date:   Tue, 8 Sep 2020 21:05:34 +0000
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References: <20200905025555.45614-1-decui@microsoft.com>
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From: Dexuan Cui <decui@microsoft.com> Sent: Friday, September 4, 2020 7:56=
 PM
>=20
> After we Stop and later Start a VM that uses Accelerated Networking (NIC
> SR-IOV), currently the VF vmbus device's Instance GUID can change, so aft=
er
> vmbus_bus_resume() -> vmbus_request_offers(), vmbus_onoffer() can not fin=
d
> the original vmbus channel of the VF, and hence we can't complete()
> vmbus_connection.ready_for_resume_event in check_ready_for_resume_event()=
,
> and the VM hangs in vmbus_bus_resume() forever.
>=20
> Fix the issue by adding a timeout, so the resuming can still succeed, and
> the saved state is not lost, and according to my test, the user can disab=
le
> Accelerated Networking and then will be able to SSH into the VM for
> further recovery. Also prevent the VM in question from suspending again.
>=20
> The host will be fixed so in future the Instance GUID will stay the same
> across hibernation.
>=20
> Fixes: d8bd2d442bb2 ("Drivers: hv: vmbus: Resume after fixing up old prim=
ary channels")
> Signed-off-by: Dexuan Cui <decui@microsoft.com>
> ---
>  drivers/hv/vmbus_drv.c | 9 +++++++--
>  1 file changed, 7 insertions(+), 2 deletions(-)

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

>=20
> diff --git a/drivers/hv/vmbus_drv.c b/drivers/hv/vmbus_drv.c
> index 910b6e90866c..946d0aba101f 100644
> --- a/drivers/hv/vmbus_drv.c
> +++ b/drivers/hv/vmbus_drv.c
> @@ -2382,7 +2382,10 @@ static int vmbus_bus_suspend(struct device *dev)
>  	if (atomic_read(&vmbus_connection.nr_chan_close_on_suspend) > 0)
>  		wait_for_completion(&vmbus_connection.ready_for_suspend_event);
>=20
> -	WARN_ON(atomic_read(&vmbus_connection.nr_chan_fixup_on_resume) !=3D 0);
> +	if (atomic_read(&vmbus_connection.nr_chan_fixup_on_resume) !=3D 0) {
> +		pr_err("Can not suspend due to a previous failed resuming\n");
> +		return -EBUSY;
> +	}
>=20
>  	mutex_lock(&vmbus_connection.channel_mutex);
>=20
> @@ -2456,7 +2459,9 @@ static int vmbus_bus_resume(struct device *dev)
>=20
>  	vmbus_request_offers();
>=20
> -	wait_for_completion(&vmbus_connection.ready_for_resume_event);
> +	if (wait_for_completion_timeout(
> +		&vmbus_connection.ready_for_resume_event, 10 * HZ) =3D=3D 0)
> +		pr_err("Some vmbus device is missing after suspending?\n");
>=20
>  	/* Reset the event for the next suspend. */
>  	reinit_completion(&vmbus_connection.ready_for_suspend_event);
> --
> 2.19.1