Re: [PATCH] bus/vmbus: fix race in sub channel creation

[Mohammed Gamal <mgamal@redhat.com>]

On Fri, 2018-11-30 at 12:24 -0800, Stephen Hemminger wrote:
> When using multiple queues, there was a race with the kernel
> in setting up the second channel. This is do due to a kernel change
> whiche does not allow accessing sysfs files for Hyper-V
> channels that are not opened.
> 
> The fix is simple, just move the logic to detect not ready
> sub channels earlier in the existing loop.
> 
> Fixes: 831dba47bd36 ("bus/vmbus: add Hyper-V virtual bus support")
> Reported-by:Mohammed Gamal <mgamal@redhat.com>
> Signed-off-by: Stephen Hemminger <sthemmin@microsoft.com>
> ---
>  drivers/bus/vmbus/linux/vmbus_uio.c | 12 ++++++------
>  1 file changed, 6 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/bus/vmbus/linux/vmbus_uio.c
> b/drivers/bus/vmbus/linux/vmbus_uio.c
> index 12e97e3a420a..38df4d724ed5 100644
> --- a/drivers/bus/vmbus/linux/vmbus_uio.c
> +++ b/drivers/bus/vmbus/linux/vmbus_uio.c
> @@ -357,6 +357,12 @@ int vmbus_uio_get_subchan(struct vmbus_channel
> *primary,
>  			continue;
>  		}
>  
> +		if (!vmbus_isnew_subchannel(primary, relid))
> +			continue;	/* Already know about you
> */
> +
> +		if (!vmbus_uio_ring_present(dev, relid))
> +			continue;	/* Ring may not be ready
> yet */
> +
>  		snprintf(subchan_path, sizeof(subchan_path),
> "%s/%lu",
>  			 chan_path, relid);
>  		err = vmbus_uio_sysfs_read(subchan_path,
> "subchannel_id",
> @@ -370,12 +376,6 @@ int vmbus_uio_get_subchan(struct vmbus_channel
> *primary,
>  		if (subid == 0)
>  			continue;	/* skip primary channel */
>  
> -		if (!vmbus_isnew_subchannel(primary, relid))
> -			continue;
> -
> -		if (!vmbus_uio_ring_present(dev, relid))
> -			continue;	/* Ring may not be ready
> yet */
> -
>  		err = vmbus_uio_sysfs_read(subchan_path,
> "monitor_id",
>  					   &monid, UINT8_MAX);
>  		if (err) {

With this patch I am now getting the following error:
[...]
Configuring Port 0 (socket 0)
hn_dev_configure():  >>
hn_rndis_link_status(): link status 0x40020006
hn_subchan_configure(): open 1 subchannels
hn_subchan_configure(): open subchannel failed: -2
hn_dev_configure(): subchannel configuration failed
Port0 dev_configure = -2
hn_dev_rx_queue_release():  >>
hn_dev_rx_queue_release():  >>
hn_dev_tx_queue_release():  >>
hn_dev_tx_queue_release():  >>
Fail to configure port 0
EAL: Error - exiting with code: 1
  Cause: Start ports failed

Apparently, no subchannels were ready. Anything I may have missed or
misconfigured?

Regards,
Mohammed