From ba537427d77cf274592f31ce94f4b4cadfad88b4 Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Wed, 9 Oct 2013 17:14:52 -0700 Subject: tcp: use ACCESS_ONCE() in tcp_update_pacing_rate() sk_pacing_rate is read by sch_fq packet scheduler at any time, with no synchronization, so make sure we update it in a sensible way. ACCESS_ONCE() is how we instruct compiler to not do stupid things, like using the memory location as a temporary variable. Signed-off-by: Eric Dumazet Signed-off-by: David S. Miller --- net/ipv4/tcp_input.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c index 47b8ab7dce9c..eb651a069a6c 100644 --- a/net/ipv4/tcp_input.c +++ b/net/ipv4/tcp_input.c @@ -755,7 +755,12 @@ static void tcp_update_pacing_rate(struct sock *sk) if (tp->srtt > 8 + 2) do_div(rate, tp->srtt); - sk->sk_pacing_rate = min_t(u64, rate, sk->sk_max_pacing_rate); + /* ACCESS_ONCE() is needed because sch_fq fetches sk_pacing_rate + * without any lock. We want to make sure compiler wont store + * intermediate values in this location. + */ + ACCESS_ONCE(sk->sk_pacing_rate) = min_t(u64, rate, + sk->sk_max_pacing_rate); } /* Calculate rto without backoff. This is the second half of Van Jacobson's -- cgit v1.2.2