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Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Dragos Tatulea , Mina Almasry Cc: netdev@vger.kernel.org, linux-rdma@vger.kernel.org, linux-kernel@vger.kernel.org, Bobby Eshleman X-Mailer: b4 0.14.3 From: Bobby Eshleman mlx5e_queue_start() deactivates and re-activates all channels but closes only the queue being restarted. mlx5e_activate_txqsq() then unconditionally calls netdev_tx_reset_queue(), zeroing the BQL counters of channels that kept their in-flight TX WQEs. The next completion then over-charges and trips the BUG_ON() in dql_completed(): kernel BUG at lib/dynamic_queue_limits.c:99! RIP: 0010:dql_completed+0x23d/0x280 Call Trace: mlx5e_poll_tx_cq+0x668/0xa60 mlx5e_napi_poll+0x5b/0x7b0 net_rx_action+0x15a/0x580 Reset BQL only when the SQ has no bytes in flight (sq->cc == sq->pc). In the case that reset is skipped, the outstanding WQEs will eventually complete and rebalance the dql. The dql->limit is carried across the reset. Fixes: b2588ea40ec9 ("net/mlx5e: Implement queue mgmt ops and single channel swap") Signed-off-by: Bobby Eshleman --- Changes in v3: - Sample sq->cc/sq->pc before setting MLX5E_SQ_STATE_ENABLED, so a concurrent mlx5e_poll_tx_cq() cannot un-charge BQL between the check and netdev_tx_reset_queue() (Sashiko: https://netdev-ai.bots.linux.dev/sashiko/#/patchset/20260729-mlx5-bql-v2-1-cdf285e586df@meta.com) - Link to v2: https://lore.kernel.org/r/20260729-mlx5-bql-v2-1-cdf285e586df@meta.com Changes in v2: - remove misleading comment (Tariq) - Link to v1: https://lore.kernel.org/r/20260728-mlx5-bql-v1-1-99a0ab77ede7@meta.com --- drivers/net/ethernet/mellanox/mlx5/core/en_main.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/drivers/net/ethernet/mellanox/mlx5/core/en_main.c b/drivers/net/ethernet/mellanox/mlx5/core/en_main.c index 7d47a1da8b6b..f0407a850ea8 100644 --- a/drivers/net/ethernet/mellanox/mlx5/core/en_main.c +++ b/drivers/net/ethernet/mellanox/mlx5/core/en_main.c @@ -1939,8 +1939,10 @@ int mlx5e_open_txqsq(struct mlx5e_channel *c, u32 tisn, int txq_ix, void mlx5e_activate_txqsq(struct mlx5e_txqsq *sq) { sq->txq = netdev_get_tx_queue(sq->netdev, sq->txq_ix); + /* Reset BQL only when the SQ has no bytes in flight. */ + if (sq->cc == sq->pc) + netdev_tx_reset_queue(sq->txq); set_bit(MLX5E_SQ_STATE_ENABLED, &sq->state); - netdev_tx_reset_queue(sq->txq); netif_tx_start_queue(sq->txq); netif_queue_set_napi(sq->netdev, sq->txq_ix, NETDEV_QUEUE_TYPE_TX, sq->cq.napi); } --- base-commit: d1000fd7995e51deec872d154e0a40d82f7a539f change-id: 20260728-mlx5-bql-84e02a5a46c8 Best regards, -- Bobby Eshleman