2018-02-16 19:02:41

by Andrea Parri

Subject: [PATCH] ptr_ring: Remove now-redundant smp_read_barrier_depends()

Because READ_ONCE() now implies smp_read_barrier_depends(), the
smp_read_barrier_depends() in __ptr_ring_consume() is redundant;
this commit removes it and updates the comments.

Signed-off-by: Andrea Parri <[email protected]>
Cc: "David S. Miller" <[email protected]>
Cc: "Michael S. Tsirkin" <[email protected]>
Cc: Jason Wang <[email protected]>
Cc: John Fastabend <[email protected]>
Cc: Eric Dumazet <[email protected]>
Cc: <[email protected]>
Cc: <[email protected]>
---
include/linux/ptr_ring.h | 7 ++++---
1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/include/linux/ptr_ring.h b/include/linux/ptr_ring.h
index b884b7794187e..ddfed1dce9369 100644
--- a/include/linux/ptr_ring.h
+++ b/include/linux/ptr_ring.h
@@ -296,13 +296,14 @@ static inline void *__ptr_ring_consume(struct ptr_ring *r)
{
void *ptr;

+ /* The READ_ONCE in __ptr_ring_peek guarantees that anyone
+ * accessing data through the pointer is up to date. Pairs
+ * with smp_wmb in __ptr_ring_produce.
+ */
ptr = __ptr_ring_peek(r);
if (ptr)
__ptr_ring_discard_one(r);

- /* Make sure anyone accessing data through the pointer is up to date. */
- /* Pairs with smp_wmb in __ptr_ring_produce. */
- smp_read_barrier_depends();
return ptr;
}

--
2.7.4

2018-02-19 16:13:56

by David Miller

Subject: Re: [PATCH] ptr_ring: Remove now-redundant smp_read_barrier_depends()

From: Andrea Parri <[email protected]>
Date: Fri, 16 Feb 2018 12:06:13 +0100

> Because READ_ONCE() now implies smp_read_barrier_depends(), the
> smp_read_barrier_depends() in __ptr_ring_consume() is redundant;
> this commit removes it and updates the comments.
>
> Signed-off-by: Andrea Parri <[email protected]>

Ok, if READ_ONCE() does a barrier now, this change makes sense.

Applied to net-next, thank you.