[PATCH bpf v2] xdp: fix race on generic receive path

[PATCH bpf v2] xdp: fix race on generic receive path

[Ilya Maximets]

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>
---

Version 2:
    * spin_lock_irqsave --> spin_lock_bh.

 include/net/xdp_sock.h |  2 ++
 net/xdp/xsk.c          | 31 ++++++++++++++++++++++---------
 2 files changed, 24 insertions(+), 9 deletions(-)

diff --git a/include/net/xdp_sock.h b/include/net/xdp_sock.h
index d074b6d60f8a..ac3c047d058c 100644
--- a/include/net/xdp_sock.h
+++ b/include/net/xdp_sock.h
@@ -67,6 +67,8 @@ struct xdp_sock {
 	 * in the SKB destructor callback.
 	 */
 	spinlock_t tx_completion_lock;
+	/* Protects generic receive. */
+	spinlock_t rx_lock;
 	u64 rx_dropped;
 };
 
diff --git a/net/xdp/xsk.c b/net/xdp/xsk.c
index a14e8864e4fa..5e0637db92ea 100644
--- a/net/xdp/xsk.c
+++ b/net/xdp/xsk.c
@@ -123,13 +123,17 @@ int xsk_generic_rcv(struct xdp_sock *xs, struct xdp_buff *xdp)
 	u64 addr;
 	int err;
 
-	if (xs->dev != xdp->rxq->dev || xs->queue_id != xdp->rxq->queue_index)
-		return -EINVAL;
+	spin_lock_bh(&xs->rx_lock);
+
+	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;
@@ -138,13 +142,21 @@ int xsk_generic_rcv(struct xdp_sock *xs, struct xdp_buff *xdp)
 	memcpy(buffer, xdp->data_meta, len + metalen);
 	addr += metalen;
 	err = xskq_produce_batch_desc(xs->rx, addr, len);
-	if (!err) {
-		xskq_discard_addr(xs->umem->fq);
-		xsk_flush(xs);
-		return 0;
-	}
+	if (err)
+		goto out_drop;
+
+	xskq_discard_addr(xs->umem->fq);
+	xskq_produce_flush_desc(xs->rx);
 
+	spin_unlock_bh(&xs->rx_lock);
+
+	xs->sk.sk_data_ready(&xs->sk);
+	return 0;
+
+out_drop:
 	xs->rx_dropped++;
+out_unlock:
+	spin_unlock_bh(&xs->rx_lock);
 	return err;
 }
 
@@ -765,6 +777,7 @@ static int xsk_create(struct net *net, struct socket *sock, int protocol,
 
 	xs = xdp_sk(sk);
 	mutex_init(&xs->mutex);
+	spin_lock_init(&xs->rx_lock);
 	spin_lock_init(&xs->tx_completion_lock);
 
 	mutex_lock(&net->xdp.lock);
-- 
2.17.1

Re: [PATCH bpf v2] xdp: fix race on generic receive path

[Magnus Karlsson]

On Wed, Jul 3, 2019 at 2:09 PM Ilya Maximets <i.maximets@samsung.com> 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.

I measured the performance degradation of rxdrop on my local machine
and it went from 2.19 to 2.08, so roughly a 5% drop. I think we can
live with this in XDP_SKB mode. If we at some later point in time need
to boost performance in this mode, let us look at it then from a
broader perspective and find the most low hanging fruit.

Thanks Ilya for this fix.

Acked-by: Magnus Karlsson <magnus.karlsson@intel.com>

> Fixes: c497176cb2e4 ("xsk: add Rx receive functions and poll support")
> Signed-off-by: Ilya Maximets <i.maximets@samsung.com>
> ---
>
> Version 2:
>     * spin_lock_irqsave --> spin_lock_bh.
>
>  include/net/xdp_sock.h |  2 ++
>  net/xdp/xsk.c          | 31 ++++++++++++++++++++++---------
>  2 files changed, 24 insertions(+), 9 deletions(-)
>
> diff --git a/include/net/xdp_sock.h b/include/net/xdp_sock.h
> index d074b6d60f8a..ac3c047d058c 100644
> --- a/include/net/xdp_sock.h
> +++ b/include/net/xdp_sock.h
> @@ -67,6 +67,8 @@ struct xdp_sock {
>          * in the SKB destructor callback.
>          */
>         spinlock_t tx_completion_lock;
> +       /* Protects generic receive. */
> +       spinlock_t rx_lock;
>         u64 rx_dropped;
>  };
>
> diff --git a/net/xdp/xsk.c b/net/xdp/xsk.c
> index a14e8864e4fa..5e0637db92ea 100644
> --- a/net/xdp/xsk.c
> +++ b/net/xdp/xsk.c
> @@ -123,13 +123,17 @@ int xsk_generic_rcv(struct xdp_sock *xs, struct xdp_buff *xdp)
>         u64 addr;
>         int err;
>
> -       if (xs->dev != xdp->rxq->dev || xs->queue_id != xdp->rxq->queue_index)
> -               return -EINVAL;
> +       spin_lock_bh(&xs->rx_lock);
> +
> +       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;
> @@ -138,13 +142,21 @@ int xsk_generic_rcv(struct xdp_sock *xs, struct xdp_buff *xdp)
>         memcpy(buffer, xdp->data_meta, len + metalen);
>         addr += metalen;
>         err = xskq_produce_batch_desc(xs->rx, addr, len);
> -       if (!err) {
> -               xskq_discard_addr(xs->umem->fq);
> -               xsk_flush(xs);
> -               return 0;
> -       }
> +       if (err)
> +               goto out_drop;
> +
> +       xskq_discard_addr(xs->umem->fq);
> +       xskq_produce_flush_desc(xs->rx);
>
> +       spin_unlock_bh(&xs->rx_lock);
> +
> +       xs->sk.sk_data_ready(&xs->sk);
> +       return 0;
> +
> +out_drop:
>         xs->rx_dropped++;
> +out_unlock:
> +       spin_unlock_bh(&xs->rx_lock);
>         return err;
>  }
>
> @@ -765,6 +777,7 @@ static int xsk_create(struct net *net, struct socket *sock, int protocol,
>
>         xs = xdp_sk(sk);
>         mutex_init(&xs->mutex);
> +       spin_lock_init(&xs->rx_lock);
>         spin_lock_init(&xs->tx_completion_lock);
>
>         mutex_lock(&net->xdp.lock);
> --
> 2.17.1
>

Re: [PATCH bpf v2] xdp: fix race on generic receive path

[William Tu]

On Wed, Jul 3, 2019 at 6:20 AM Magnus Karlsson
<magnus.karlsson@gmail.com> wrote:
>
> On Wed, Jul 3, 2019 at 2:09 PM Ilya Maximets <i.maximets@samsung.com> 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.
>
> I measured the performance degradation of rxdrop on my local machine
> and it went from 2.19 to 2.08, so roughly a 5% drop. I think we can
> live with this in XDP_SKB mode. If we at some later point in time need
> to boost performance in this mode, let us look at it then from a
> broader perspective and find the most low hanging fruit.
>
> Thanks Ilya for this fix.
>
> Acked-by: Magnus Karlsson <magnus.karlsson@intel.com>
>
> > Fixes: c497176cb2e4 ("xsk: add Rx receive functions and poll support")
> > Signed-off-by: Ilya Maximets <i.maximets@samsung.com>
> > ---

Tested on my machine and works ok.
Tested-by: William Tu <u9012063@gmail.com>

Re: [PATCH bpf v2] xdp: fix race on generic receive path

[Daniel Borkmann]

On 07/03/2019 02:09 PM, 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>

Applied, thanks!