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From:   Magnus Karlsson <magnus.karlsson@gmail.com>
Date:   Wed, 2 Jun 2021 10:29:58 +0200
Message-ID: <CAJ8uoz2sT9iyqjWcsUDQZqZCVoCfpqgM7TseOTqeCzOuChAwww@mail.gmail.com>
Subject: Re: [PATCH net-next] xsk: Return -EINVAL instead of -EBUSY after
 xsk_get_pool_from_qid() fails
To:     Wang Hai <wanghai38@huawei.com>
Cc:     =?UTF-8?B?QmrDtnJuIFTDtnBlbA==?= <bjorn@kernel.org>,
        "Karlsson, Magnus" <magnus.karlsson@intel.com>,
        Jonathan Lemon <jonathan.lemon@gmail.com>,
        "David S. Miller" <davem@davemloft.net>,
        Jakub Kicinski <kuba@kernel.org>,
        Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        Jesper Dangaard Brouer <hawk@kernel.org>,
        John Fastabend <john.fastabend@gmail.com>,
        Network Development <netdev@vger.kernel.org>,
        bpf <bpf@vger.kernel.org>,
        open list <linux-kernel@vger.kernel.org>
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On Wed, Jun 2, 2021 at 6:02 AM Wang Hai <wanghai38@huawei.com> wrote:
>
> xsk_get_pool_from_qid() fails not because the device's queues are busy,
> but because the queue_id exceeds the current number of queues.
> So when it fails, it is better to return -EINVAL instead of -EBUSY.
>
> Signed-off-by: Wang Hai <wanghai38@huawei.com>
> ---
>  net/xdp/xsk_buff_pool.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/net/xdp/xsk_buff_pool.c b/net/xdp/xsk_buff_pool.c
> index 8de01aaac4a0..30ece117117a 100644
> --- a/net/xdp/xsk_buff_pool.c
> +++ b/net/xdp/xsk_buff_pool.c
> @@ -135,7 +135,7 @@ int xp_assign_dev(struct xsk_buff_pool *pool,
>                 return -EINVAL;
>
>         if (xsk_get_pool_from_qid(netdev, queue_id))
> -               return -EBUSY;
> +               return -EINVAL;

I guess your intent here is to return -EINVAL only when the queue_id
is larger than the number of active queues. But this patch also
changes the return code when the queue id is already in use and in
that case we should continue to return -EBUSY. As this function is
used by a number of drivers, the easiest way to accomplish this is to
introduce a test for queue_id out of bounds before this if-statement
and return -EINVAL there.

>         pool->netdev = netdev;
>         pool->queue_id = queue_id;
> --
> 2.17.1
>