netdev - Re: [PATCH iwl-net v2 6/6] ice: do not bring the VSI up, if it was down before the XDP setup

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Message-ID: <1d6c2ce8-9d98-4cdd-a59c-7486eed9908b@intel.com>
Date: Wed, 24 Jul 2024 11:40:26 -0700
From: Jacob Keller <jacob.e.keller@...el.com>
To: Larysa Zaremba <larysa.zaremba@...el.com>,
	<intel-wired-lan@...ts.osuosl.org>
CC: Tony Nguyen <anthony.l.nguyen@...el.com>, "David S. Miller"
	<davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski
	<kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, Alexei Starovoitov
	<ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>, "Jesper Dangaard
 Brouer" <hawk@...nel.org>, John Fastabend <john.fastabend@...il.com>, "Maciej
 Fijalkowski" <maciej.fijalkowski@...el.com>, <netdev@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, <bpf@...r.kernel.org>,
	<magnus.karlsson@...el.com>, Michal Kubiak <michal.kubiak@...el.com>,
	Wojciech Drewek <wojciech.drewek@...el.com>, Amritha Nambiar
	<amritha.nambiar@...el.com>
Subject: Re: [PATCH iwl-net v2 6/6] ice: do not bring the VSI up, if it was
 down before the XDP setup



On 7/24/2024 9:48 AM, Larysa Zaremba wrote:
> After XDP configuration is completed, we bring the interface up
> unconditionally, regardless of its state before the call to .ndo_bpf().
> 
> Preserve the information whether the interface had to be brought down and
> later bring it up only in such case.
> 
> Fixes: efc2214b6047 ("ice: Add support for XDP")
> Reviewed-by: Wojciech Drewek <wojciech.drewek@...el.com>
> Signed-off-by: Larysa Zaremba <larysa.zaremba@...el.com>
> ---
>  drivers/net/ethernet/intel/ice/ice_main.c | 7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/net/ethernet/intel/ice/ice_main.c b/drivers/net/ethernet/intel/ice/ice_main.c
> index d7cc641643f8..d83cde431fa5 100644
> --- a/drivers/net/ethernet/intel/ice/ice_main.c
> +++ b/drivers/net/ethernet/intel/ice/ice_main.c
> @@ -3000,8 +3000,8 @@ ice_xdp_setup_prog(struct ice_vsi *vsi, struct bpf_prog *prog,
>  		   struct netlink_ext_ack *extack)
>  {
>  	unsigned int frame_size = vsi->netdev->mtu + ICE_ETH_PKT_HDR_PAD;
> -	bool if_running = netif_running(vsi->netdev);
>  	int ret = 0, xdp_ring_err = 0;
> +	bool if_running;
>  
>  	if (prog && !prog->aux->xdp_has_frags) {
>  		if (frame_size > ice_max_xdp_frame_size(vsi)) {
> @@ -3018,8 +3018,11 @@ ice_xdp_setup_prog(struct ice_vsi *vsi, struct bpf_prog *prog,
>  		return 0;
>  	}
>  
> +	if_running = netif_running(vsi->netdev) &&
> +		     !test_and_set_bit(ICE_VSI_DOWN, vsi->state);
> +
>  	/* need to stop netdev while setting up the program for Rx rings */
> -	if (if_running && !test_and_set_bit(ICE_VSI_DOWN, vsi->state)) {
> +	if (if_running) {
>  		ret = ice_down(vsi);
>  		if (ret) {
>  			NL_SET_ERR_MSG_MOD(extack, "Preparing device for XDP attach failed");

This diff lacks the appropriate context that can help explain how it works:

> 
>         if (if_running)
>                 ret = ice_up(vsi);
> 
>         if (!ret && prog)
>                 ice_vsi_rx_napi_schedule(vsi);
> 
>         return (ret || xdp_ring_err) ? -ENOMEM : 0;

By changing if_running to include the VSI state flag, we ensure the call
to ice_up is correctly conditional.

Good fix. If I understand right, it depends on the other synchronization
fixes to work correctly so that the VSI state won't be changed on us.

Reviewed-by: Jacob Keller <jacob.e.keller@...el.com>