Subject: Re: [PATCH net-next] hv_netvsc: Fix race condition on Multi-Send Data field

From: Vitaly Kuznetsov <[email-masked]>
Date: Fri, 11 Dec 2015 14:52:32 +0100

Vitaly Kuznetsov <[email-masked]> writes:

> Haiyang Zhang <[email-masked]> writes:
>
>> In commit 2a04ae8acb14 ("hv_netvsc: remove locking in netvsc_send()"), the
>> locking for MSD (Multi-Send Data) field was removed. This could cause a
>> race condition between RNDIS control messages and data packets processing,
>> because these two types of traffic are not synchronized.
>> This patch fixes this issue by sending control messages out directly
>> without reading MSD field.
>>
>> Signed-off-by: Haiyang Zhang <[email-masked]>
>> Reviewed-by: K. Y. Srinivasan <[email-masked]>
>> ---
>>  drivers/net/hyperv/netvsc.c |    9 +++++++++
>>  1 files changed, 9 insertions(+), 0 deletions(-)
>>
>> diff --git a/drivers/net/hyperv/netvsc.c b/drivers/net/hyperv/netvsc.c
>> index 02bab9a..059fc52 100644
>> --- a/drivers/net/hyperv/netvsc.c
>> +++ b/drivers/net/hyperv/netvsc.c
>> @@ -867,6 +867,14 @@ int netvsc_send(struct hv_device *device,
>>  	packet->send_buf_index = NETVSC_INVALID_INDEX;
>>  	packet->cp_partial = false;
>>  
>> +	/* Send control message directly without accessing msd (Multi-Send
>> +	 * Data) field which may be changed during data packet processing.
>> +	 */
>> +	if (!skb) {
>> +		cur_send = packet;
>> +		goto send_now;
>> +	}
>> +
>
> Is is supposed to be applied on top of some other patches? It doesn't
> compile on top of current net-next:
>
> drivers/net/hyperv/netvsc.c: In function ‘netvsc_send’:
> drivers/net/hyperv/netvsc.c:865:7: error: ‘skb’ undeclared (first use in
> this function)
>   if (!skb) {
>          ^
>
> Did you mean to check rndis_msg instead (as skb is not defined here)?

Oh, my bad, it was me who was looking at the wrong branch... Sorry for
the noise.

>
>>  	msdp = &net_device->msd[q_idx];
>>  
>>  	/* batch packets in send buffer if possible */
>> @@ -939,6 +947,7 @@ int netvsc_send(struct hv_device *device,
>>  		}
>>  	}
>>  
>> +send_now:
>>  	if (cur_send)
>>  		ret = netvsc_send_pkt(cur_send, net_device, pb, skb);
>
> I suppose we untangle these two pathes completely: let
> rndis_filter_send_request() call netvsc_send_pkt() directly. Please see
> my patch attached (note: it should be split in 3 patches if
> submitted). If you like the idea I can send it.

This patch will need some changes but the suggestion still stands: let's
untangle sending data and control messages.

-- 
  Vitaly