net: hns3: fix data race between ring->next_to_clean

hns3_clean_tx_ring calls hns3_nic_reclaim_one_desc to clean
buffers and set ring->next_to_clean, then hns3_nic_net_xmit
reuses the cleaned buffers. But there are no memory barriers
when buffers gets recycled, so the recycled buffers can be
corrupted.

This patch uses smp_store_release to update ring->next_to_clean
and smp_load_acquire to read ring->next_to_clean to properly
hand off buffers from hns3_clean_tx_ring to hns3_nic_net_xmit.

Fixes: 76ad4f0e ("net: hns3: Add support of HNS3 Ethernet Driver for hip08 SoC")
Signed-off-by: Yunsheng Lin <linyunsheng@huawei.com>
Signed-off-by: Peng Li <lipeng321@huawei.com>
Signed-off-by: Huazhong Tan <tanhuazhong@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/hisilicon/hns3/hns3_enet.c

@@ -2214,14 +2214,22 @@ static void hns3_reuse_buffer(struct hns3_enet_ring *ring, int i)
 static void hns3_nic_reclaim_one_desc(struct hns3_enet_ring *ring, int *bytes,
 				      int *pkts)
 {
-	struct hns3_desc_cb *desc_cb = &ring->desc_cb[ring->next_to_clean];
+	int ntc = ring->next_to_clean;
+	struct hns3_desc_cb *desc_cb;
 
+	desc_cb = &ring->desc_cb[ntc];
 	(*pkts) += (desc_cb->type == DESC_TYPE_SKB);
 	(*bytes) += desc_cb->length;
 	/* desc_cb will be cleaned, after hnae3_free_buffer_detach*/
-	hns3_free_buffer_detach(ring, ring->next_to_clean);
+	hns3_free_buffer_detach(ring, ntc);
 
-	ring_ptr_move_fw(ring, next_to_clean);
+	if (++ntc == ring->desc_num)
+		ntc = 0;
+
+	/* This smp_store_release() pairs with smp_load_acquire() in
+	 * ring_space called by hns3_nic_net_xmit.
+	 */
+	smp_store_release(&ring->next_to_clean, ntc);
 }
 
 static int is_valid_clean_head(struct hns3_enet_ring *ring, int h)

drivers/net/ethernet/hisilicon/hns3/hns3_enet.h

@@ -581,8 +581,11 @@ union l4_hdr_info {
 
 static inline int ring_space(struct hns3_enet_ring *ring)
 {
-	int begin = ring->next_to_clean;
-	int end = ring->next_to_use;
+	/* This smp_load_acquire() pairs with smp_store_release() in
+	 * hns3_nic_reclaim_one_desc called by hns3_clean_tx_ring.
+	 */
+	int begin = smp_load_acquire(&ring->next_to_clean);
+	int end = READ_ONCE(ring->next_to_use);
 
 	return ((end >= begin) ? (ring->desc_num - end + begin) :
 			(begin - end)) - 1;