[dpdk-dev] [PATCH] kni: fix wrong mbuf alloc count in kni_allocate_mbufs

[Ferruh Yigit]

On 5/31/2021 1:09 PM, wangyunjian wrote:
> From: Yunjian Wang <wangyunjian at huawei.com>
> 
> In kni_allocate_mbufs(), we alloc mbuf for alloc_q as this code.
> allocq_free = (kni->alloc_q->read - kni->alloc_q->write - 1) \
> 		& (MAX_MBUF_BURST_NUM - 1);
> The value of allocq_free maybe zero (e.g 32 & (32 - 1) = 0), and
> it will not fill the alloc_q. When the alloc_q's free count is
> zero, it will drop the packet in kernel kni.
> 

nack

Both 'read' & 'write' pointers can be max 'len-1',
so 'read - write - 1' can't be 'len'.
For above example first part can't be '32'.

But if you are observing a problem, can you please describe it a little more, it
may be because of something else.

> In this patch, we set the allocq_free as the min between
> MAX_MBUF_BURST_NUM and the free count of the alloc_q.
> 
> Signed-off-by: Cheng Liu <liucheng11 at huawei.com>
> Signed-off-by: Yunjian Wang <wangyunjian at huawei.com>
> ---
>  lib/kni/rte_kni.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/lib/kni/rte_kni.c b/lib/kni/rte_kni.c
> index 9dae6a8d7c..20d8f20cef 100644
> --- a/lib/kni/rte_kni.c
> +++ b/lib/kni/rte_kni.c
> @@ -677,8 +677,9 @@ kni_allocate_mbufs(struct rte_kni *kni)
>  		return;
>  	}
>  
> -	allocq_free = (kni->alloc_q->read - kni->alloc_q->write - 1)
> -			& (MAX_MBUF_BURST_NUM - 1);
> +	allocq_free = kni_fifo_free_count(kni->alloc_q);
> +	allocq_free = (allocq_free > MAX_MBUF_BURST_NUM) ?
> +		      MAX_MBUF_BURST_NUM : allocq_free;
>  	for (i = 0; i < allocq_free; i++) {
>  		pkts[i] = rte_pktmbuf_alloc(kni->pktmbuf_pool);
>  		if (unlikely(pkts[i] == NULL)) {
>