netdev - Re: [PATCH bpf] xsk: Clear pool even for inactive queues

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Date:   Tue, 19 Jan 2021 15:08:36 +0100
From:   Björn Töpel <bjorn.topel@...el.com>
To:     Maxim Mikityanskiy <maximmi@...lanox.com>,
        Magnus Karlsson <magnus.karlsson@...el.com>
Cc:     Jonathan Lemon <jonathan.lemon@...il.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        John Fastabend <john.fastabend@...il.com>,
        netdev@...r.kernel.org, bpf@...r.kernel.org
Subject: Re: [PATCH bpf] xsk: Clear pool even for inactive queues

On 2021-01-18 17:03, Maxim Mikityanskiy wrote:
> The number of queues can change by other means, rather than ethtool. For
> example, attaching an mqprio qdisc with num_tc > 1 leads to creating
> multiple sets of TX queues, which may be then destroyed when mqprio is
> deleted. If an AF_XDP socket is created while mqprio is active,
> dev->_tx[queue_id].pool will be filled, but then real_num_tx_queues may
> decrease with deletion of mqprio, which will mean that the pool won't be
> NULLed, and a further increase of the number of TX queues may expose a
> dangling pointer.
> 
> To avoid any potential misbehavior, this commit clears pool for RX and
> TX queues, regardless of real_num_*_queues, still taking into
> consideration num_*_queues to avoid overflows.
> 
> Fixes: 1c1efc2af158 ("xsk: Create and free buffer pool independently from umem")
> Fixes: a41b4f3c58dd ("xsk: simplify xdp_clear_umem_at_qid implementation")
> Signed-off-by: Maxim Mikityanskiy <maximmi@...lanox.com>

Thanks, Maxim!

Acked-by: Björn Töpel <bjorn.topel@...el.com>

> ---
>   net/xdp/xsk.c | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/net/xdp/xsk.c b/net/xdp/xsk.c
> index 8037b04a9edd..4a83117507f5 100644
> --- a/net/xdp/xsk.c
> +++ b/net/xdp/xsk.c
> @@ -108,9 +108,9 @@ EXPORT_SYMBOL(xsk_get_pool_from_qid);
>   
>   void xsk_clear_pool_at_qid(struct net_device *dev, u16 queue_id)
>   {
> -	if (queue_id < dev->real_num_rx_queues)
> +	if (queue_id < dev->num_rx_queues)
>   		dev->_rx[queue_id].pool = NULL;
> -	if (queue_id < dev->real_num_tx_queues)
> +	if (queue_id < dev->num_tx_queues)
>   		dev->_tx[queue_id].pool = NULL;
>   }
>   
>