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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: 965a990984 ("xsk: add support for bind for Rx")
Fixes: ac98d8aab6 ("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>
This commit is contained in:
Björn Töpel 2018-10-05 13:25:15 +02:00 committed by Daniel Borkmann
parent df1ea77bc5
commit 541d7fdd76
2 changed files with 11 additions and 13 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

11
net/xdp/xdp_umem.c
View File

@ -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();
}
spin_lock_irqsave(&umem->xsk_list_lock, flags);
list_del_rcu(&xs->list);
spin_unlock_irqrestore(&umem->xsk_list_lock, flags);
}
/* The umem is stored both in the _rx struct and the _tx struct as we do

13
net/xdp/xsk.c
View File

@ -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);