kni: fix mbuf allocation for kernel side use

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, for example :
The ring size is 1024. After init, write = read = 0. Then we fill
kni->alloc_q to full. At this time, write = 1023, read = 0.

Then the kernel send 32 packets to userspace. At this time, write
= 1023, read = 32. And then the userspace receive this 32 packets.
Then fill the kni->alloc_q, (32 - 1023 - 1) & 31 = 0, fill nothing.
...
Then the kernel send 32 packets to userspace. At this time, write
= 1023, read = 992. And then the userspace receive this 32 packets.
Then fill the kni->alloc_q, (992 - 1023 - 1) & 31 = 0, fill nothing.

Then the kernel send 32 packets to userspace. The kni->alloc_q only
has 31 mbufs and will drop one packet.

Absolutely, this is a special scene. Normally, it will fill some
mbufs everytime, but may not enough for the kernel to use.

In this patch, we always keep the kni->alloc_q to full for the kernel
to use.

Fixes: 49da4e82cf94 ("kni: allocate no more mbuf than empty slots in queue")
Cc: stable@dpdk.org
Signed-off-by: Cheng Liu <liucheng11@huawei.com>
Signed-off-by: Yunjian Wang <wangyunjian@huawei.com>
Acked-by: Ferruh Yigit <ferruh.yigit@intel.com>
Acked-by: Ajit Khaparde <ajit.khaparde@broadcom.com>

diff --git a/lib/kni/rte_kni.c b/lib/kni/rte_kni.c
index 9dae6a8..eb24b0d 100644 (file)
--- 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)) {