On Mon, Oct 8, 2018 at 10:41 AM Björn Töpel <bjorn.to...@gmail.com> wrote:
>
> From: Björn Töpel <bjorn.to...@intel.com>
>
> The XSKMAP update and delete functions called synchronize_net(), which
> can sleep. It is not allowed to sleep during an RCU read section.
>
> Instead we need to make sure that the sock sk_destruct (xsk_destruct)
> function is asynchronously called after an RCU grace period. Setting
> the SOCK_RCU_FREE flag for XDP sockets takes care of this.
>
> Fixes: fbfc504a24f5 ("bpf: introduce new bpf AF_XDP map type
> BPF_MAP_TYPE_XSKMAP")
> Reported-by: Eric Dumazet <eric.duma...@gmail.com>
> Signed-off-by: Björn Töpel <bjorn.to...@intel.com>
Acked-by: Song Liu <songliubrav...@fb.com>
> ---
> kernel/bpf/xskmap.c | 10 ++--------
> net/xdp/xsk.c | 2 ++
> 2 files changed, 4 insertions(+), 8 deletions(-)
>
> diff --git a/kernel/bpf/xskmap.c b/kernel/bpf/xskmap.c
> index 9f8463afda9c..47147c9e184d 100644
> --- a/kernel/bpf/xskmap.c
> +++ b/kernel/bpf/xskmap.c
> @@ -192,11 +192,8 @@ static int xsk_map_update_elem(struct bpf_map *map, void
> *key, void *value,
> sock_hold(sock->sk);
>
> old_xs = xchg(&m->xsk_map[i], xs);
> - if (old_xs) {
> - /* Make sure we've flushed everything. */
> - synchronize_net();
> + if (old_xs)
> sock_put((struct sock *)old_xs);
> - }
>
> sockfd_put(sock);
> return 0;
> @@ -212,11 +209,8 @@ static int xsk_map_delete_elem(struct bpf_map *map, void
> *key)
> return -EINVAL;
>
> old_xs = xchg(&m->xsk_map[k], NULL);
> - if (old_xs) {
> - /* Make sure we've flushed everything. */
> - synchronize_net();
> + if (old_xs)
> sock_put((struct sock *)old_xs);
> - }
>
> return 0;
> }
> diff --git a/net/xdp/xsk.c b/net/xdp/xsk.c
> index 0577cd49aa72..07156f43d295 100644
> --- a/net/xdp/xsk.c
> +++ b/net/xdp/xsk.c
> @@ -754,6 +754,8 @@ static int xsk_create(struct net *net, struct socket
> *sock, int protocol,
> sk->sk_destruct = xsk_destruct;
> sk_refcnt_debug_inc(sk);
>
> + sock_set_flag(sk, SOCK_RCU_FREE);
> +
> xs = xdp_sk(sk);
> mutex_init(&xs->mutex);
> spin_lock_init(&xs->tx_completion_lock);
> --
> 2.17.1
>
