net/mlx5e: Fix napi poll with zero budget

napi->poll can be called with budget 0, e.g. in netpoll scenarios
where the caller only wants to poll TX rings
(poll_one_napi@net/core/netpoll.c).

The below commit changed RX polling from "while" loop to "do {} while",
which caused to ignore the initial budget and handle at least one RX
packet.

This fixes the following warning:
[ 2852.049194] mlx5e_napi_poll+0x0/0x260 [mlx5_core] exceeded budget in poll
[ 2852.049195] ------------[ cut here ]------------
[ 2852.049195] WARNING: CPU: 0 PID: 25691 at net/core/netpoll.c:171 netpoll_poll_dev+0x18a/0x1a0

Fixes: 4b7dfc992514 ("net/mlx5e: Early-return on empty completion queues")
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>
Reviewed-by: Tariq Toukan <tariqt@mellanox.com>
Reported-by: Martin KaFai Lau <kafai@fb.com>
Tested-by: Martin KaFai Lau <kafai@fb.com>
Cc: kernel-team@fb.com
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>

1 files changed, 6 insertions, 4 deletions

diff --git a/drivers/net/ethernet/mellanox/mlx5/core/en_txrx.c b/drivers/net/ethernet/mellanox/mlx5/core/en_txrx.c
index e906b754415c..ab92298eafc3 100644
--- a/drivers/net/ethernet/mellanox/mlx5/core/en_txrx.c
+++ b/drivers/net/ethernet/mellanox/mlx5/core/en_txrx.c
@@ -49,7 +49,7 @@ int mlx5e_napi_poll(struct napi_struct *napi, int budget)
         struct mlx5e_channel *c = container_of(napi, struct mlx5e_channel,
                                                napi);
         bool busy = false;
-        int work_done;
+        int work_done = 0;
         int i;
 
         for (i = 0; i < c->num_tc; i++)
@@ -58,15 +58,17 @@ int mlx5e_napi_poll(struct napi_struct *napi, int budget)
         if (c->xdp)
                 busy |= mlx5e_poll_xdpsq_cq(&c->rq.xdpsq.cq);
 
-        work_done = mlx5e_poll_rx_cq(&c->rq.cq, budget);
-        busy |= work_done == budget;
+        if (likely(budget)) { /* budget=0 means: don't poll rx rings */
+                work_done = mlx5e_poll_rx_cq(&c->rq.cq, budget);
+                busy |= work_done == budget;
+        }
 
         busy |= c->rq.post_wqes(&c->rq);
 
         if (busy) {
                 if (likely(mlx5e_channel_no_affinity_change(c)))
                         return budget;
-                if (work_done == budget)
+                if (budget && work_done == budget)
                         work_done--;
         }