Re: [PATCH iwl-net] i40e: Fix XDP program unloading while removing the driver

[Maciej Fijalkowski <maciej.fijalkowski@intel.com>]

On Thu, May 16, 2024 at 06:41:08PM +0200, Michal Kubiak wrote:
> The commit 6533e558c650 ("i40e: Fix reset path while removing
> the driver") introduced a new PF state "__I40E_IN_REMOVE" to block
> modifying the XDP program while the driver is being removed.
> Unfortunately, such a change is useful only if the ".ndo_bpf()"
> callback was called out of the rmmod context because unloading the
> existing XDP program is also a part of driver removing procedure.
> In other words, from the rmmod context the driver is expected to
> unload the XDP program without reporting any errors. Otherwise,
> the kernel warning with callstack is printed out to dmesg.
> 
> Example failing scenario:
>  1. Load the i40e driver.
>  2. Load the XDP program.
>  3. Unload the i40e driver (using "rmmod" command).
> 
> Fix this by improving checks in ".ndo_bpf()" to determine if that
> callback was called from the removing context and if the kernel
> wants to unload the XDP program. Allow for unloading the XDP program
> in such a case.
> 
> Fixes: 6533e558c650 ("i40e: Fix reset path while removing the driver")
> Reviewed-by: Wojciech Drewek <wojciech.drewek@intel.com>
> Signed-off-by: Michal Kubiak <michal.kubiak@intel.com>

Acked-by: Maciej Fijalkowski <maciej.fijalkowski@intel.com>

> ---
>  drivers/net/ethernet/intel/i40e/i40e_main.c | 19 ++++++++++++++-----
>  1 file changed, 14 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/net/ethernet/intel/i40e/i40e_main.c b/drivers/net/ethernet/intel/i40e/i40e_main.c
> index ffb9f9f15c52..19fc043e351f 100644
> --- a/drivers/net/ethernet/intel/i40e/i40e_main.c
> +++ b/drivers/net/ethernet/intel/i40e/i40e_main.c
> @@ -13264,6 +13264,20 @@ static int i40e_xdp_setup(struct i40e_vsi *vsi, struct bpf_prog *prog,
>  	bool need_reset;
>  	int i;
>  
> +	/* Called from netdev unregister context. Unload the XDP program. */
> +	if (vsi->netdev->reg_state == NETREG_UNREGISTERING) {
> +		xdp_features_clear_redirect_target(vsi->netdev);
> +		old_prog = xchg(&vsi->xdp_prog, NULL);
> +		if (old_prog)
> +			bpf_prog_put(old_prog);
> +
> +		return 0;
> +	}
> +
> +	/* VSI shall be deleted in a moment, just return EINVAL */
> +	if (test_bit(__I40E_IN_REMOVE, pf->state))
> +		return -EINVAL;
> +
>  	/* Don't allow frames that span over multiple buffers */
>  	if (vsi->netdev->mtu > frame_size - I40E_PACKET_HDR_PAD) {
>  		NL_SET_ERR_MSG_MOD(extack, "MTU too large for linear frames and XDP prog does not support frags");
> @@ -13272,14 +13286,9 @@ static int i40e_xdp_setup(struct i40e_vsi *vsi, struct bpf_prog *prog,
>  
>  	/* When turning XDP on->off/off->on we reset and rebuild the rings. */
>  	need_reset = (i40e_enabled_xdp_vsi(vsi) != !!prog);
> -
>  	if (need_reset)
>  		i40e_prep_for_reset(pf);
>  
> -	/* VSI shall be deleted in a moment, just return EINVAL */
> -	if (test_bit(__I40E_IN_REMOVE, pf->state))
> -		return -EINVAL;
> -
>  	old_prog = xchg(&vsi->xdp_prog, prog);
>  
>  	if (need_reset) {
> -- 
> 2.33.1
>