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

From: Jakub Kicinski <jakub.kicinski@netronome.com>
To: Ilya Maximets <i.maximets@samsung.com>
Cc: netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
	bpf@vger.kernel.org, xdp-newbies@vger.kernel.org,
	"David S. Miller" <davem@davemloft.net>,
	"Björn Töpel" <bjorn.topel@intel.com>,
	"Magnus Karlsson" <magnus.karlsson@intel.com>,
	"Jonathan Lemon" <jonathan.lemon@gmail.com>,
	"Alexei Starovoitov" <ast@kernel.org>,
	"Daniel Borkmann" <daniel@iogearbox.net>
Subject: Re: [PATCH bpf] xdp: fix race on generic receive path
Date: Tue, 2 Jul 2019 17:40:14 -0700	[thread overview]
Message-ID: <20190702174014.005a3166@cakuba.netronome.com> (raw)
In-Reply-To: <20190702143634.19688-1-i.maximets@samsung.com>

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@samsung.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?

> +	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;