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 <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 47b8ab7..eb651a0 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -755,7 +755,12 @@
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