netdev - Re: [PATCH iwl-net v3 5/6] ice: remove ICE_CFG_BUSY locking from AF

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Message-ID: <Zsckdsyjwfglf6RX@boxer>
Date: Thu, 22 Aug 2024 13:43:50 +0200
From: Maciej Fijalkowski <maciej.fijalkowski@...el.com>
To: Larysa Zaremba <larysa.zaremba@...el.com>
CC: <intel-wired-lan@...ts.osuosl.org>, Tony Nguyen
	<anthony.l.nguyen@...el.com>, "David S. Miller" <davem@...emloft.net>, "Jacob
 Keller" <jacob.e.keller@...el.com>, 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>,
	<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>, Chandan Kumar Rout
	<chandanx.rout@...el.com>
Subject: Re: [PATCH iwl-net v3 5/6] ice: remove ICE_CFG_BUSY locking from
 AF_XDP code

On Mon, Aug 19, 2024 at 12:05:42PM +0200, Larysa Zaremba wrote:
> Locking used in ice_qp_ena() and ice_qp_dis() does pretty much nothing,
> because ICE_CFG_BUSY is a state flag that is supposed to be set in a PF
> state, not VSI one. Therefore it does not protect the queue pair from
> e.g. reset.
> 
> Despite being useless, it still can deadlock the unfortunate functions that
> have fell into the same ICE_CFG_BUSY-VSI trap. This happens if ice_qp_ena
> returns an error.

I believe the last sentence is not valid after our recent fixes around xsk
and tx timeouts.

> 
> Remove ICE_CFG_BUSY locking from ice_qp_dis() and ice_qp_ena().
> 
> Fixes: 2d4238f55697 ("ice: Add support for AF_XDP")
> Reviewed-by: Wojciech Drewek <wojciech.drewek@...el.com>
> Reviewed-by: Jacob Keller <jacob.e.keller@...el.com>
> Tested-by: Chandan Kumar Rout <chandanx.rout@...el.com>
> Signed-off-by: Larysa Zaremba <larysa.zaremba@...el.com>

Reviewed-by: Maciej Fijalkowski <maciej.fijalkowski@...el.com>

> ---
>  drivers/net/ethernet/intel/ice/ice_xsk.c | 9 ---------
>  1 file changed, 9 deletions(-)
> 
> diff --git a/drivers/net/ethernet/intel/ice/ice_xsk.c b/drivers/net/ethernet/intel/ice/ice_xsk.c
> index 8693509efbe7..5dee829bfc47 100644
> --- a/drivers/net/ethernet/intel/ice/ice_xsk.c
> +++ b/drivers/net/ethernet/intel/ice/ice_xsk.c
> @@ -165,7 +165,6 @@ static int ice_qp_dis(struct ice_vsi *vsi, u16 q_idx)
>  	struct ice_q_vector *q_vector;
>  	struct ice_tx_ring *tx_ring;
>  	struct ice_rx_ring *rx_ring;
> -	int timeout = 50;
>  	int fail = 0;
>  	int err;
>  
> @@ -176,13 +175,6 @@ static int ice_qp_dis(struct ice_vsi *vsi, u16 q_idx)
>  	rx_ring = vsi->rx_rings[q_idx];
>  	q_vector = rx_ring->q_vector;
>  
> -	while (test_and_set_bit(ICE_CFG_BUSY, vsi->state)) {
> -		timeout--;
> -		if (!timeout)
> -			return -EBUSY;
> -		usleep_range(1000, 2000);
> -	}
> -
>  	synchronize_net();
>  	netif_carrier_off(vsi->netdev);
>  	netif_tx_stop_queue(netdev_get_tx_queue(vsi->netdev, q_idx));
> @@ -261,7 +253,6 @@ static int ice_qp_ena(struct ice_vsi *vsi, u16 q_idx)
>  		netif_tx_start_queue(netdev_get_tx_queue(vsi->netdev, q_idx));
>  		netif_carrier_on(vsi->netdev);
>  	}
> -	clear_bit(ICE_CFG_BUSY, vsi->state);
>  
>  	return fail;
>  }
> -- 
> 2.43.0
>