netdev - Re: [PATCH bpf] xdp: fix race on generic receive path

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Date:   Wed, 3 Jul 2019 15:03:03 +0300
From:   Ilya Maximets <i.maximets@...sung.com>
To:     Jakub Kicinski <jakub.kicinski@...ronome.com>
Cc:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        bpf@...r.kernel.org, xdp-newbies@...r.kernel.org,
        "David S. Miller" <davem@...emloft.net>,
        Björn Töpel <bjorn.topel@...el.com>,
        Magnus Karlsson <magnus.karlsson@...el.com>,
        Jonathan Lemon <jonathan.lemon@...il.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>
Subject: Re: [PATCH bpf] xdp: fix race on generic receive path

On 03.07.2019 3:40, Jakub Kicinski wrote:
> On Tue,  2 Jul 2019 17:36:34 +0300, Ilya Maximets wrote:
>> Unlike driver mode, generic xdp receive could be triggered
>> by different threads on different CPU cores at the same time
>> leading to the fill and rx queue breakage. For example, this
>> could happen while sending packets from two processes to the
>> first interface of veth pair while the second part of it is
>> open with AF_XDP socket.
>>
>> Need to take a lock for each generic receive to avoid race.
>>
>> Fixes: c497176cb2e4 ("xsk: add Rx receive functions and poll support")
>> Signed-off-by: Ilya Maximets <i.maximets@...sung.com>
> 
>> diff --git a/net/xdp/xsk.c b/net/xdp/xsk.c
>> index a14e8864e4fa..19f41d2b670c 100644
>> --- a/net/xdp/xsk.c
>> +++ b/net/xdp/xsk.c
>> @@ -119,17 +119,22 @@ int xsk_generic_rcv(struct xdp_sock *xs, struct xdp_buff *xdp)
>>  {
>>  	u32 metalen = xdp->data - xdp->data_meta;
>>  	u32 len = xdp->data_end - xdp->data;
>> +	unsigned long flags;
>>  	void *buffer;
>>  	u64 addr;
>>  	int err;
>>  
>> -	if (xs->dev != xdp->rxq->dev || xs->queue_id != xdp->rxq->queue_index)
>> -		return -EINVAL;
>> +	spin_lock_irqsave(&xs->rx_lock, flags);
> 
> Why _irqsave, rather than _bh?

Yes, spin_lock_bh() is enough here. Will change in v2.
Thanks.

> 
>> +	if (xs->dev != xdp->rxq->dev || xs->queue_id != xdp->rxq->queue_index) {
>> +		err = -EINVAL;
>> +		goto out_unlock;
>> +	}
>>  
>>  	if (!xskq_peek_addr(xs->umem->fq, &addr) ||
>>  	    len > xs->umem->chunk_size_nohr - XDP_PACKET_HEADROOM) {
>> -		xs->rx_dropped++;
>> -		return -ENOSPC;
>> +		err = -ENOSPC;
>> +		goto out_drop;
>>  	}
>>  
>>  	addr += xs->umem->headroom;
> 
> 
>