Messages in this thread Patch in this message | | | From | "Paul E. McKenney" <> | Subject | [PATCH 08/19] net/ipv4/tcp_input.c: Kill off ACCESS_ONCE() | Date | Mon, 23 Oct 2017 14:07:18 -0700 |
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From: Mark Rutland <mark.rutland@arm.com>
For several reasons, it is desirable to use {READ,WRITE}_ONCE() in preference to ACCESS_ONCE(), and new code is expected to use one of the former. So far, there's been no reason to change most existing uses of ACCESS_ONCE(), as these aren't currently harmful.
However, for some features it is necessary to instrument reads and writes separately, which is not possible with ACCESS_ONCE(). This distinction is critical to correct operation.
It's possible to transform the bulk of kernel code using the Coccinelle script below. However, this doesn't handle comments, leaving references to ACCESS_ONCE() instances which have been removed. As a preparatory step, this patch converts the IPv4 TCP input code and comments to use {READ,WRITE}_ONCE() consistently.
---- virtual patch
@ depends on patch @ expression E1, E2; @@
- ACCESS_ONCE(E1) = E2 + WRITE_ONCE(E1, E2)
@ depends on patch @ expression E; @@
- ACCESS_ONCE(E) + READ_ONCE(E) ----
Signed-off-by: Mark Rutland <mark.rutland@arm.com> Cc: David S. Miller <davem@davemloft.net> --- net/ipv4/tcp_input.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c index c5d7656beeee..133e7e4d94b5 100644 --- a/net/ipv4/tcp_input.c +++ b/net/ipv4/tcp_input.c @@ -815,12 +815,12 @@ static void tcp_update_pacing_rate(struct sock *sk) if (likely(tp->srtt_us)) do_div(rate, tp->srtt_us); - /* ACCESS_ONCE() is needed because sch_fq fetches sk_pacing_rate + /* WRITE_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); + WRITE_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 -- 2.5.2
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