linux-kernel - Re: [PATCH net-next 03/12] ptr_ring: READ/WRITE_ONCE for __ptr_ring

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Message-ID: <2b7d17c0-ef6c-0aad-9b47-0fb8ad78cc3a@redhat.com>
Date:   Fri, 26 Jan 2018 10:37:58 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     "Michael S. Tsirkin" <mst@...hat.com>, linux-kernel@...r.kernel.org
Cc:     netdev@...r.kernel.org, John Fastabend <john.fastabend@...il.com>,
        David Miller <davem@...emloft.net>
Subject: Re: [PATCH net-next 03/12] ptr_ring: READ/WRITE_ONCE for
 __ptr_ring_empty



On 2018年01月26日 07:36, Michael S. Tsirkin wrote:
> Lockless __ptr_ring_empty requires that consumer head is read and
> written at once, atomically. Annotate accordingly to make sure compiler
> does it correctly.  Switch locked callers to __ptr_ring_peek which does
> not support the lockless operation.
>
> Signed-off-by: Michael S. Tsirkin <mst@...hat.com>
> ---
>   include/linux/ptr_ring.h | 11 ++++++++---
>   1 file changed, 8 insertions(+), 3 deletions(-)
>
> diff --git a/include/linux/ptr_ring.h b/include/linux/ptr_ring.h
> index 8594c7b..9a72d8f 100644
> --- a/include/linux/ptr_ring.h
> +++ b/include/linux/ptr_ring.h
> @@ -196,7 +196,9 @@ static inline void *__ptr_ring_peek(struct ptr_ring *r)
>    */
>   static inline bool __ptr_ring_empty(struct ptr_ring *r)
>   {
> -	return !__ptr_ring_peek(r);
> +	if (likely(r->size))
> +		return !r->queue[READ_ONCE(r->consumer_head)];
> +	return true;
>   }

So after patch 8, __ptr_ring_peek() did:

static inline void *__ptr_ring_peek(struct ptr_ring *r)
{
     if (likely(r->size))
         return READ_ONCE(r->queue[r->consumer_head]);
     return NULL;
}

Looks like a duplication.

Thanks