net/mlx5e: Do not update BQL of old txqs during channel reconfiguration

net/mlx5e: Do not update BQL of old txqs during channel reconfiguration

During channel reconfiguration (e.g., ethtool private flags changes),
the driver can trigger a kernel BUG_ON in dql_completed() with the error
"kernel BUG at lib/dynamic_queue_limits.c:99".

The issue occurs in the following sequence:

During mlx5e_safe_switch_params(), old channels are deactivated via
mlx5e_deactivate_txqsq(). New channels are created and activated, taking
ownership of the netdev_queues and their BQL state.

When old channels are closed via mlx5e_close_txqsq(), there may be
pending TX descriptors (sq->cc != sq->pc) that were in-flight during the
deactivation.

mlx5e_free_txqsq_descs() frees these pending descriptors and attempts to
complete them via netdev_tx_completed_queue().

However, the BQL state (dql->num_queued and dql->num_completed) have
been reset in mlx5e_activate_txqsq and belong to the new queue owner,
leading to dql->num_queued - dql->num_completed < nbytes.

This triggers BUG_ON(count > num_queued - num_completed) in
dql_completed().

Fixes: 3b88a535a8e1 ("net/mlx5e: Defer channels closure to reduce interface down time")
Signed-off-by: Tariq Toukan <tariqt@nvidia.com>
Signed-off-by: William Tu <witu@nvidia.com>
Reviewed-by: Dragos Tatulea <dtatulea@nvidia.com>
Link: https://patch.msgid.link/1765284977-1363052-9-git-send-email-tariqt@nvidia.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>