Re: [EXTERNAL] Re: [PATCH v3] net/netvsc: fix number Tx queues > Rx queues

[Ferruh Yigit <ferruh.yigit@amd.com>]

On 4/11/2024 9:45 PM, Alan Elder wrote:
>> -----Original Message-----
>> From: Ferruh Yigit <ferruh.yigit@amd.com>
>> Sent: Thursday, April 11, 2024 7:38 AM
>> To: Alan Elder <alan.elder@microsoft.com>; Long Li <longli@microsoft.com>;
>> Andrew Rybchenko <andrew.rybchenko@oktetlabs.ru>
>> Cc: dev@dpdk.org; stephen <stephen@networkplumber.org>
>> Subject: [EXTERNAL] Re: [PATCH v3] net/netvsc: fix number Tx queues > Rx
>> queues
>>
>> On 3/19/2024 2:16 PM, Alan Elder wrote:
>>> The previous code allowed the number of Tx queues to be set higher
>>> than the number of Rx queues.  If a packet was sent on a Tx queue with
>>> index
>>>> = number Rx queues there was a segfault.
>>> This commit fixes the issue by creating an Rx queue for every Tx queue
>>> meaning that an event buffer is allocated to handle receiving Tx
>>> completion messages.
>>>
>>> mbuf pool and Rx ring are not allocated for these additional Rx queues
>>> and RSS configuration ensures that no packets are received on them.
>>>
>>> Fixes: 4e9c73e96e83 ("net/netvsc: add Hyper-V network device")
>>> Cc: sthemmin@microsoft.com
>>> Cc: stable@dpdk.org
>>>
>>> Signed-off-by: Alan Elder <alan.elder@microsoft.com>
>>>
>>
>> Hi Alan,
>>
>> What is the root cause of the crash, is it in driver scope or application?
> 
> Hi Ferruh,
> 
> The root cause of the crash was in the driver - a packet received on a Tx queue that had no corresponding Rx queue would cause the dev->data->rx_queues[] array to be accessed past the length of the array.
> 
> https://github.com/DPDK/dpdk/blob/main/drivers/net/netvsc/hn_rxtx.c#L1071
> 
> 

Why there is an access to Rx queue when processing Tx queue?

A backtrace of the crash can help to understand the issue, can you
please include this in commit log, plus some explanation why crash happens?

Thanks,
ferruh