From: Daniel Borkmann <daniel@iogearbox•net>
To: Lawrence Brakmo <brakmo@fb•com>, netdev <netdev@vger•kernel.org>
Cc: Kernel Team <Kernel-team@fb•com>, Blake Matheny <bmatheny@fb•com>,
Alexei Starovoitov <ast@fb•com>,
David Ahern <dsa@cumulusnetworks•com>
Subject: Re: [RFC PATCH net-next v2 10/15] bpf: Add support for changing congestion control
Date: Tue, 20 Jun 2017 00:34:06 +0200 [thread overview]
Message-ID: <5948515E.1090607@iogearbox.net> (raw)
In-Reply-To: <59B6F12A-9740-4177-BCB3-72CD65EB1225@fb.com>
On 06/18/2017 04:39 AM, Lawrence Brakmo wrote:
> On 6/16/17, 6:58 AM, "Daniel Borkmann" <daniel@iogearbox•net> wrote:
[...]
> > /* Change congestion control for socket */
> > -int tcp_set_congestion_control(struct sock *sk, const char *name)
> > +int tcp_set_congestion_control(struct sock *sk, const char *name, bool load)
> > {
> > struct inet_connection_sock *icsk = inet_csk(sk);
> > const struct tcp_congestion_ops *ca;
> > @@ -344,7 +344,10 @@ int tcp_set_congestion_control(struct sock *sk, const char *name)
> > return -EPERM;
> >
> > rcu_read_lock();
> > - ca = __tcp_ca_find_autoload(name);
> > + if (!load)
> > + ca = tcp_ca_find(name);
> > + else
> > + ca = __tcp_ca_find_autoload(name);
>
> From BPF program side, we call with !load since we're not allowed
> to sleep under RCU, that's correct ...
>
> > /* No change asking for existing value */
> > if (ca == icsk->icsk_ca_ops) {
> > icsk->icsk_ca_setsockopt = 1;
> > @@ -352,8 +355,10 @@ int tcp_set_congestion_control(struct sock *sk, const char *name)
> > }
> > if (!ca)
> > err = -ENOENT;
> > + else if (!load)
> > + icsk->icsk_ca_ops = ca;
>
> ... but don't we also need to hold a module ref in this case as done
> below?
>
> Meaning, tcp_ca_find() could return a ca that was previously loaded
> to the tcp_cong_list as module, then resulting in ref count imbalance
> when set from BPF?
>
> As I mentioned above, this can be called before congestion has been
> initialized (op <= BPF_SOCKET_OPS_NEEDS_ECN) in which case
> tcp_init_congestion_control will be called later. If op > ..OPS_NEEDS_ECN
> then bpf_setsockopt() will call the reinit_congestion_control().
>
> But this points to an issue where someone else could call
> tcp_set_congestion_control() with load == false not knowing they
> need to call either init or reinit. I will add a comment to the function
> to make it clear.
Hm, I'm not sure it answers my question. What I meant was that from BPF
prog, you're setting tcp_set_congestion_control(..., false) so if
tcp_ca_find() returns a ca that was loaded earlier as a from a module
(so it becomes available in tcp_cong_list), the above...
[...]
else if (!load)
icsk->icsk_ca_ops = ca;
[...]
... will basically prevent the later try_module_get() on the ca. So any
later tcp_reinit_congestion_control() or tcp_init_congestion_control()
will still run not having the refcount held on the owner module. Meaning
a module unload would let the machine crash due to the refcnt imbalance?
What am I missing?
next prev parent reply other threads:[~2017-06-19 22:34 UTC|newest]
Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-06-15 20:08 [RFC PATCH net-next v2 00/15] bpf: BPF support for socket ops Lawrence Brakmo
2017-06-15 20:08 ` [RFC PATCH net-next v2 01/15] " Lawrence Brakmo
2017-06-16 12:07 ` Daniel Borkmann
2017-06-16 23:41 ` Lawrence Brakmo
2017-06-19 18:44 ` Daniel Borkmann
2017-06-19 20:49 ` Lawrence Brakmo
2017-06-17 21:48 ` Lawrence Brakmo
2017-06-19 18:52 ` Daniel Borkmann
2017-06-19 20:49 ` Lawrence Brakmo
2017-06-15 20:08 ` [RFC PATCH net-next v2 02/15] bpf: program to load socketops BPF programs Lawrence Brakmo
2017-06-15 20:08 ` [RFC PATCH net-next v2 03/15] bpf: Support for per connection SYN/SYN-ACK RTOs Lawrence Brakmo
2017-06-15 20:08 ` [RFC PATCH net-next v2 04/15] bpf: Sample bpf program to set " Lawrence Brakmo
2017-06-15 20:08 ` [RFC PATCH net-next v2 05/15] bpf: Support for setting initial receive window Lawrence Brakmo
2017-06-15 20:08 ` [RFC PATCH net-next v2 06/15] bpf: Sample bpf program to set initial window Lawrence Brakmo
2017-06-15 20:08 ` [RFC PATCH net-next v2 07/15] bpf: Add setsockopt helper function to bpf Lawrence Brakmo
2017-06-16 13:27 ` Daniel Borkmann
2017-06-17 23:17 ` Lawrence Brakmo
2017-06-15 20:08 ` [RFC PATCH net-next v2 08/15] bpf: Add TCP connection BPF callbacks Lawrence Brakmo
2017-06-15 20:08 ` [RFC PATCH net-next v2 09/15] bpf: Sample BPF program to set buffer sizes Lawrence Brakmo
2017-06-15 20:08 ` [RFC PATCH net-next v2 10/15] bpf: Add support for changing congestion control Lawrence Brakmo
2017-06-16 13:58 ` Daniel Borkmann
2017-06-18 2:39 ` Lawrence Brakmo
2017-06-19 22:34 ` Daniel Borkmann [this message]
2017-06-20 0:35 ` Lawrence Brakmo
2017-06-15 20:08 ` [RFC PATCH net-next v2 11/15] bpf: Sample BPF program to set " Lawrence Brakmo
2017-06-15 20:08 ` [RFC PATCH net-next v2 12/15] bpf: Adds support for setting initial cwnd Lawrence Brakmo
2017-06-15 20:08 ` [RFC PATCH net-next v2 13/15] bpf: Sample BPF program to set " Lawrence Brakmo
2017-06-15 20:08 ` [RFC PATCH net-next v2 14/15] bpf: Adds support for setting sndcwnd clamp Lawrence Brakmo
2017-06-15 20:08 ` [RFC PATCH net-next v2 15/15] bpf: Sample bpf program to set " Lawrence Brakmo
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