From: Bobby Eshleman <bobbyeshleman@gmail.com>
To: Saeed Mahameed <saeedm@nvidia.com>,
Tariq Toukan <tariqt@nvidia.com>, Mark Bloch <mbloch@nvidia.com>,
Leon Romanovsky <leon@kernel.org>,
Andrew Lunn <andrew+netdev@lunn.ch>,
"David S. Miller" <davem@davemloft.net>,
Eric Dumazet <edumazet@google.com>,
Jakub Kicinski <kuba@kernel.org>,
Paolo Abeni <pabeni@redhat.com>,
Dragos Tatulea <dtatulea@nvidia.com>,
Mina Almasry <almasrymina@google.com>
Cc: netdev@vger.kernel.org, linux-rdma@vger.kernel.org,
linux-kernel@vger.kernel.org,
Bobby Eshleman <bobbyeshleman@meta.com>
Subject: [PATCH net v2] net/mlx5e: fix BQL reset on SQ re-activation
Date: Wed, 29 Jul 2026 18:57:35 -0700 [thread overview]
Message-ID: <20260729-mlx5-bql-v2-1-cdf285e586df@meta.com> (raw)
From: Bobby Eshleman <bobbyeshleman@meta.com>
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:
<IRQ>
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 <bobbyeshleman@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 4a8351f95b27..44834890a409 100644
--- a/drivers/net/ethernet/mellanox/mlx5/core/en_main.c
+++ b/drivers/net/ethernet/mellanox/mlx5/core/en_main.c
@@ -1940,7 +1940,9 @@ void mlx5e_activate_txqsq(struct mlx5e_txqsq *sq)
{
sq->txq = netdev_get_tx_queue(sq->netdev, sq->txq_ix);
set_bit(MLX5E_SQ_STATE_ENABLED, &sq->state);
- netdev_tx_reset_queue(sq->txq);
+ /* Reset BQL only when the SQ has no bytes in flight. */
+ if (sq->cc == sq->pc)
+ 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: ec83512ba345b1e415ca491509a7a952db84c4c7
change-id: 20260728-mlx5-bql-84e02a5a46c8
Best regards,
--
Bobby Eshleman <bobbyeshleman@meta.com>
reply other threads:[~2026-07-30 1:57 UTC|newest]
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