Commit-ID: a9da6f29baf6b61fc94f9768638ee54e9bff173c
Gitweb: https://git.kernel.org/tip/a9da6f29baf6b61fc94f9768638ee54e9bff173c
Author: Mark Rutland <[email protected]>
AuthorDate: Mon, 23 Oct 2017 14:07:18 -0700
Committer: Ingo Molnar <[email protected]>
CommitDate: Wed, 25 Oct 2017 11:01:00 +0200
locking/atomics, net/ipv4/tcp_input.c: Convert ACCESS_ONCE() to
READ_ONCE()/WRITE_ONCE()
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 <[email protected]>
Signed-off-by: Paul E. McKenney <[email protected]>
Cc: David S. Miller <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Link:
http://lkml.kernel.org/r/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>
---
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 7eec338..74480e0 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
