Commit 541d7fdd authored Oct 05, 2018 by Björn Töpel Committed by Daniel Borkmann Oct 08, 2018

xsk: proper AF_XDP socket teardown ordering



The AF_XDP socket struct can exist in three different, implicit
states: setup, bound and released. Setup is prior the socket has been
bound to a device. Bound is when the socket is active for receive and
send. Released is when the process/userspace side of the socket is
released, but the sock object is still lingering, e.g. when there is a
reference to the socket in an XSKMAP after process termination.

The Rx fast-path code uses the "dev" member of struct xdp_sock to
check whether a socket is bound or relased, and the Tx code uses the
struct xdp_umem "xsk_list" member in conjunction with "dev" to
determine the state of a socket.

However, the transition from bound to released did not tear the socket
down in correct order.

On the Rx side "dev" was cleared after synchronize_net() making the
synchronization useless. On the Tx side, the internal queues were
destroyed prior removing them from the "xsk_list".

This commit corrects the cleanup order, and by doing so
xdp_del_sk_umem() can be simplified and one synchronize_net() can be
removed.

Fixes: 965a9909 ("xsk: add support for bind for Rx")
Fixes: ac98d8aa ("xsk: wire upp Tx zero-copy functions")
Reported-by: Jesper Dangaard Brouer <brouer@redhat.com>
Signed-off-by: Björn Töpel <bjorn.topel@intel.com>
Acked-by: Song Liu <songliubraving@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

parent df1ea77b

net/xdp/xdp_umem.c

+3 −8

Original line number	Diff line number	Diff line
		@@ -32,14 +32,9 @@ void xdp_del_sk_umem(struct xdp_umem umem, struct xdp_sock xs)
		{
		unsigned long flags;

		if (xs->dev) {
		spin_lock_irqsave(&umem->xsk_list_lock, flags);
		list_del_rcu(&xs->list);
		spin_unlock_irqrestore(&umem->xsk_list_lock, flags);

		if (umem->zc)
		synchronize_net();
		}
		}

		/* The umem is stored both in the _rx struct and the _tx struct as we do

net/xdp/xsk.c

+8 −5

Original line number	Diff line number	Diff line
		@@ -355,12 +355,18 @@ static int xsk_release(struct socket *sock)
		local_bh_enable();

		if (xs->dev) {
		struct net_device *dev = xs->dev;

		/* Wait for driver to stop using the xdp socket. */
		synchronize_net();
		dev_put(xs->dev);
		xdp_del_sk_umem(xs->umem, xs);
		xs->dev = NULL;
		synchronize_net();
		dev_put(dev);
		}

		xskq_destroy(xs->rx);
		xskq_destroy(xs->tx);

		sock_orphan(sk);
		sock->sk = NULL;

		@@ -714,9 +720,6 @@ static void xsk_destruct(struct sock *sk)
		if (!sock_flag(sk, SOCK_DEAD))
		return;

		xskq_destroy(xs->rx);
		xskq_destroy(xs->tx);
		xdp_del_sk_umem(xs->umem, xs);
		xdp_put_umem(xs->umem);

		sk_refcnt_debug_dec(sk);

Admin message