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tcp: use ACCESS_ONCE() in tcp_update_pacing_rate()

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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>
This commit is contained in:
Eric Dumazet 2013-10-09 17:14:52 -07:00 committed by David S. Miller
parent 634fb979e8
commit ba537427d7
1 changed files with 6 additions and 1 deletions
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7
net/ipv4/tcp_input.c
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@ -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