Re: [PATCH net] net/mlx5e: Update netdev features only after a successful ringparam set

["Björn Töpel" <bjorn@kernel.org>]

Dimitri Daskalakis <dimitri.daskalakis1@gmail.com> writes:

> From: Dimitri Daskalakis <daskald@meta.com>
>
> mlx5 couples HW-GRO with tcp-data-split. If a user sets rx-gro-hw on ->
> tcp-data-split on -> rx-gro-hw off, the driver will leave HW-GRO on.
> mlx5e_ethtool_set_tcp_data_split() calls netdev_update_features() when
> tcp-data-split goes from enabled to disabled in case HW-GRO needs to be
> released. mlx5e_fix_features() reads the new HDS config from
> dev->cfg_pending, so HW-GRO is released before all ring parameters are
> validated.
>
> If the subsequent call to mlx5e_ethtool_set_ringparam() fails, the
> ethtool core discards the pending change and reports tcp-data-split
> enabled. The device is no longer splitting, and subsequent ring changes
> are blocked.
>
> Move the call to netdev_update_features() after
> mlx5e_ethtool_set_ringparam() exits successfully.
>
> The issue was discovered by manual code inspection during review of
> a change that stops mlx5 users from disabling tcp-data-split. It was
> reproduced on a ConnectX-7 with ethtool alone.
>
> Steps to reproduce:
> ethtool -K eth0 rx-gro-hw on
> ethtool -G eth0 tcp-data-split on
> ethtool -K eth0 rx-gro-hw off # HW-GRO kept on for tcp-data-split
>
> ethtool -G eth0 tcp-data-split off rx 1 # de-sync driver & kernel state
>  netlink error: mlx5_core: rx (1) < min (16)
>  netlink error: Invalid argument
>
> ethtool -G eth0 rx 1024 # valid ring changes are now blocked
>  netlink error: mlx5_core: TCP-data-split is not supported when GRO HW is disabled
>  netlink error: Invalid argument
>
> This is not a terminal state, users can recover by setting rx-gro-hw on.
> With the fix, the failing ringparam set leaves rx-gro-hw on and later
> ring changes succeed.
>
> Fixes: 46bcce5dfd33 ("net/mlx5e: Support ethtool tcp-data-split settings")
> Reported-by: Björn Töpel <bjorn@kernel.org>
> Closes: https://lore.kernel.org/87se2grw3d.fsf@all.your.base.are.belong.to.us/
> Signed-off-by: Dimitri Daskalakis <daskald@meta.com>

Reviewed-by: Björn Töpel <bjorn@kernel.org>