net/mlx5e: Wrap mlx5e_trap_napi_poll into rcu_read_lock

The body of mlx5e_napi_poll is wrapped into rcu_read_lock to be able to
read the XDP program pointer using rcu_dereference. However, the trap RQ
NAPI doesn't use rcu_read_lock, because the trap RQ works only in the
non-linear mode, and mlx5e_skb_from_cqe_nonlinear, until recently,
didn't support XDP and didn't call rcu_dereference.

Starting from the cited commit, mlx5e_skb_from_cqe_nonlinear supports
XDP and calls rcu_dereference, but mlx5e_trap_napi_poll doesn't wrap it
into rcu_read_lock. It leads to RCU-lockdep warnings like this:

    WARNING: suspicious RCU usage

This commit fixes the issue by adding an rcu_read_lock to
mlx5e_trap_napi_poll, similarly to mlx5e_napi_poll.

Fixes: ea5d49bd ("net/mlx5e: Add XDP multi buffer support to the non-linear legacy RQ")
Signed-off-by: Maxim Mikityanskiy <maximmi@nvidia.com>
Reviewed-by: Tariq Toukan <tariqt@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>

drivers/net/ethernet/mellanox/mlx5/core/en/trap.c

@@ -14,19 +14,26 @@ static int mlx5e_trap_napi_poll(struct napi_struct *napi, int budget)
 	bool busy = false;
 	int work_done = 0;
 
+	rcu_read_lock();
+
 	ch_stats->poll++;
 
 	work_done = mlx5e_poll_rx_cq(&rq->cq, budget);
 	busy |= work_done == budget;
 	busy |= rq->post_wqes(rq);
 
-	if (busy)
-		return budget;
+	if (busy) {
+		work_done = budget;
+		goto out;
+	}
 
 	if (unlikely(!napi_complete_done(napi, work_done)))
-		return work_done;
+		goto out;
 
 	mlx5e_cq_arm(&rq->cq);
+
+out:
+	rcu_read_unlock();
 	return work_done;
 }