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Date: Wed, 09 Oct 2013 17:14:52 -0700 From: Eric Dumazet <eric.dumazet@...il.com> To: David Miller <davem@...emloft.net> Cc: netdev <netdev@...r.kernel.org> Subject: [PATCH net-next] tcp: use ACCESS_ONCE() in tcp_update_pacing_rate() From: Eric Dumazet <edumazet@...gle.com> 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 <edumazet@...gle.com> --- 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 47b8ab7..b441fe6 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 -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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