Den mån 8 okt. 2018 kl 17:31 skrev Eric Dumazet <eric.duma...@gmail.com>:
>
> On 05/02/2018 04:01 AM, Björn Töpel wrote:
> > From: Björn Töpel <bjorn.to...@intel.com>
> >
> > The xskmap is yet another BPF map, very much inspired by
> > dev/cpu/sockmap, and is a holder of AF_XDP sockets. A user application
> > adds AF_XDP sockets into the map, and by using the bpf_redirect_map
> > helper, an XDP program can redirect XDP frames to an AF_XDP socket.
> >
> > Note that a socket that is bound to certain ifindex/queue index will
> > *only* accept XDP frames from that netdev/queue index. If an XDP
> > program tries to redirect from a netdev/queue index other than what
> > the socket is bound to, the frame will not be received on the socket.
> >
> > A socket can reside in multiple maps.
> >
> > v3: Fixed race and simplified code.
> > v2: Removed one indirection in map lookup.
> >
> > Signed-off-by: Björn Töpel <bjorn.to...@intel.com>
> > ---
> > include/linux/bpf.h | 25 +++++
> > include/linux/bpf_types.h | 3 +
> > include/net/xdp_sock.h | 7 ++
> > include/uapi/linux/bpf.h | 1 +
> > kernel/bpf/Makefile | 3 +
> > kernel/bpf/verifier.c | 8 +-
> > kernel/bpf/xskmap.c | 239
> > ++++++++++++++++++++++++++++++++++++++++++++++
> > net/xdp/xsk.c | 5 +
> > 8 files changed, 289 insertions(+), 2 deletions(-)
> > create mode 100644 kernel/bpf/xskmap.c
> >
>
> This function is called under rcu_read_lock() , from map_update_elem()
>
> > +
> > +static int xsk_map_update_elem(struct bpf_map *map, void *key, void *value,
> > + u64 map_flags)
> > +{
> > + struct xsk_map *m = container_of(map, struct xsk_map, map);
> > + u32 i = *(u32 *)key, fd = *(u32 *)value;
> > + struct xdp_sock *xs, *old_xs;
> > + struct socket *sock;
> > + int err;
> > +
> > + if (unlikely(map_flags > BPF_EXIST))
> > + return -EINVAL;
> > + if (unlikely(i >= m->map.max_entries))
> > + return -E2BIG;
> > + if (unlikely(map_flags == BPF_NOEXIST))
> > + return -EEXIST;
> > +
> > + sock = sockfd_lookup(fd, &err);
> > + if (!sock)
> > + return err;
> > +
> > + if (sock->sk->sk_family != PF_XDP) {
> > + sockfd_put(sock);
> > + return -EOPNOTSUPP;
> > + }
> > +
> > + xs = (struct xdp_sock *)sock->sk;
> > +
> > + if (!xsk_is_setup_for_bpf_map(xs)) {
> > + sockfd_put(sock);
> > + return -EOPNOTSUPP;
> > + }
> > +
> > + sock_hold(sock->sk);
> > +
> > + old_xs = xchg(&m->xsk_map[i], xs);
> > + if (old_xs) {
> > + /* Make sure we've flushed everything. */
>
> So it is illegal to call synchronize_net(), since it is a reschedule point.
>
Thanks for finding and pointing this out, Eric!
I'll have look and get back with a patch.
Björn
> > + synchronize_net();
> > + sock_put((struct sock *)old_xs);
> > + }
> > +
> > + sockfd_put(sock);
> > + return 0;
> > +}
> >
>
>
>
