Cong Wang wrote:
> From: Cong Wang <cong.wang@xxxxxxxxxxxxx>
>
> UDP already has udp_sendmsg() which takes lock_sock() inside.
> We have to build ->sendmsg_locked() on top of it, by adding
> a new parameter for whether the sock has been locked.
>
> Cc: John Fastabend <john.fastabend@xxxxxxxxx>
> Cc: Daniel Borkmann <daniel@xxxxxxxxxxxxx>
> Cc: Jakub Sitnicki <jakub@xxxxxxxxxxxxxx>
> Cc: Lorenz Bauer <lmb@xxxxxxxxxxxxxx>
> Signed-off-by: Cong Wang <cong.wang@xxxxxxxxxxxxx>
> ---
> include/net/udp.h | 1 +
> net/ipv4/af_inet.c | 1 +
> net/ipv4/udp.c | 30 +++++++++++++++++++++++-------
> 3 files changed, 25 insertions(+), 7 deletions(-)
[...]
> -int udp_sendmsg(struct sock *sk, struct msghdr *msg, size_t len)
> +static int __udp_sendmsg(struct sock *sk, struct msghdr *msg, size_t len, bool locked)
> {
The lock_sock is also taken by BPF_CGROUP_RUN_PROG_UDP4_SENDMSG_LOCK() in
udp_sendmsg(),
if (cgroup_bpf_enabled(BPF_CGROUP_UDP4_SENDMSG) && !connected) {
err = BPF_CGROUP_RUN_PROG_UDP4_SENDMSG_LOCK(sk,
(struct sockaddr *)usin, &ipc.addr);
so that will also need to be handled.
It also looks like sk_dst_set() wants the sock lock to be held, but I'm not
seeing how its covered in the current code,
static inline void
__sk_dst_set(struct sock *sk, struct dst_entry *dst)
{
struct dst_entry *old_dst;
sk_tx_queue_clear(sk);
sk->sk_dst_pending_confirm = 0;
old_dst = rcu_dereference_protected(sk->sk_dst_cache,
lockdep_sock_is_held(sk));
rcu_assign_pointer(sk->sk_dst_cache, dst);
dst_release(old_dst);
}
I guess this could trip lockdep now, I'll dig a bit more Monday and see
if its actually the case.
In general I don't really like code that wraps locks in 'if' branches
like this. It seem fragile to me. I didn't walk every path in the code
to see if a lock is taken in any of the called functions but it looks
like ip_send_skb() can call into netfilter code and may try to take
the sock lock.
Do we need this locked send at all? We use it in sk_psock_backlog
but that routine needs an optimization rewrite for TCP anyways.
Its dropping a lot of performance on the floor for no good reason.
.John
