[PATCH net v3] net/mlx5e: fix BQL reset on SQ re-activation

[PATCH net v3] net/mlx5e: fix BQL reset on SQ re-activation

[Bobby Eshleman]

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 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 <bobbyeshleman@meta.com>

Re: [PATCH net v3] net/mlx5e: fix BQL reset on SQ re-activation

[Tariq Toukan]

On 04/08/2026 2:47, Bobby Eshleman wrote:
> 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>

Reviewed-by: Tariq Toukan <tariqt@nvidia.com>

Thanks.

> ---
> 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,

Re: [PATCH net v3] net/mlx5e: fix BQL reset on SQ re-activation

[Bobby Eshleman]

On Tue, Aug 04, 2026 at 11:23:53AM +0300, Tariq Toukan wrote:
> 
> 
> On 04/08/2026 2:47, Bobby Eshleman wrote:
> > 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>
> 
> Reviewed-by: Tariq Toukan <tariqt@nvidia.com>
> 
> Thanks.

Thanks Tariq, and my apologies for forgetting to carry the R-b forward.

> 
> > ---
> > 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,
> 

Re: [PATCH net v3] net/mlx5e: fix BQL reset on SQ re-activation

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to netdev/net.git (main)
by Jakub Kicinski <kuba@kernel.org>:

On Mon, 03 Aug 2026 16:47:29 -0700 you wrote:
> 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():
> 
> [...]

Here is the summary with links:
  - [net,v3] net/mlx5e: fix BQL reset on SQ re-activation
    https://git.kernel.org/netdev/net/c/e7386770be1b

You are awesome, thank you!
-- 
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