tcp: use ACCESS_ONCE() in tcp_update_pacing_rate() (ba537427) · Commits · 戴 / test

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@google.com> Signed-off-by:

David S. Miller <davem@davemloft.net>

net/ipv4/tcp_input.c

+6 −1

Original line number	Diff line number	Diff line
		@@ -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

Admin message