Re: [dpdk-dev] [PATCH v5] net/mlx5: fix mutex unlock in txpp cleanup

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

On 11/11/2021 7:06 AM, Slava Ovsiienko wrote:
> Hi, Ferruh
> 
>> -----Original Message-----
>> From: Ferruh Yigit <ferruh.yigit@intel.com>
>> Sent: Wednesday, November 10, 2021 18:57
>> To: Chengfeng Ye <cyeaa@connect.ust.hk>; david.marchand@redhat.com;
>> Slava Ovsiienko <viacheslavo@nvidia.com>; Shahaf Shuler
>> <shahafs@nvidia.com>; Matan Azrad <matan@nvidia.com>
>> Cc: dev@dpdk.org; stable@dpdk.org
>> Subject: Re: [dpdk-dev] [PATCH v5] net/mlx5: fix mutex unlock in txpp
>> cleanup
>>
>> On 10/12/2021 11:02 AM, Chengfeng Ye wrote:
>>> The lock sh->txpp.mutex was not correctly released on one path of
>>> cleanup function return, potentially causing the deadlock.
>>>
>>> Fixes: d133f4cdb7 ("net/mlx5: create clock queue for packet pacing")
>>> Cc: stable@dpdk.org
>>>
>>> Signed-off-by: Chengfeng Ye <cyeaa@connect.ust.hk>
>>> ---
>>>    drivers/net/mlx5/mlx5_txpp.c | 6 +++++-
>>>    1 file changed, 5 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/drivers/net/mlx5/mlx5_txpp.c
>>> b/drivers/net/mlx5/mlx5_txpp.c index 4f6da9f2d1..0ece788a84 100644
>>> --- a/drivers/net/mlx5/mlx5_txpp.c
>>> +++ b/drivers/net/mlx5/mlx5_txpp.c
>>> @@ -961,8 +961,12 @@ mlx5_txpp_stop(struct rte_eth_dev *dev)
>>>    	MLX5_ASSERT(!ret);
>>>    	RTE_SET_USED(ret);
>>>    	MLX5_ASSERT(sh->txpp.refcnt);
>>> -	if (!sh->txpp.refcnt || --sh->txpp.refcnt)
>>> +	if (!sh->txpp.refcnt || --sh->txpp.refcnt) {
>>> +		ret = pthread_mutex_unlock(&sh->txpp.mutex);
>>> +		MLX5_ASSERT(!ret);
>>> +		RTE_SET_USED(ret);
>>
>> Is this 'RTE_SET_USED()' need to be used multiple times for same variable?
> mmm, It seems "claim_zero()" macro would be better here:
> 
> claim_zero(pthread_mutex_lock(&sh->txpp.mutex));
> 
> I will provide the cleanup patch, thank you for noticing that
> 
>> This usage looks ugly, I can see why it is used but I wonder if this can be
>> solved differently, what about something like following:
>>
>>    #ifdef RTE_LIBRTE_MLX5_DEBUG
>>     #define MLX5_ASSERT(exp) RTE_VERIFY(exp)
>>    #else
>>     #ifdef RTE_ENABLE_ASSERT
>>      #define MLX5_ASSERT(exp) RTE_ASSERT(exp)
>>     #else
>>      #define MLX5_ASSERT(exp) RTE_SET_USED(exp)
>>     #endif
>>    #endif
> It would directly replace MLX5_ASSERT(exp) with RTE_SET_USED(exp)
> if there is neither RTE_ENABLE_ASSERT nor RTE_LIBRTE_MLX5_DEBUG.
> We would not like to drop the "not used" check functionality at all , right?
> 

The suggestion was to prevent following kind of usage:
  	MLX5_ASSERT(!ret);
  	RTE_SET_USED(ret);

I assume you need above usage when a variable is used only in the 'MLX5_ASSERT',
if there is a way to prevent warning in that case without 'RTE_SET_USED' that
may be better.