From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751914AbeAZCiU (ORCPT ); Thu, 25 Jan 2018 21:38:20 -0500 Received: from mx1.redhat.com ([209.132.183.28]:51166 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751816AbeAZCiT (ORCPT ); Thu, 25 Jan 2018 21:38:19 -0500 Subject: Re: [PATCH net-next 08/12] ptr_ring: prevent queue load/store tearing To: "Michael S. Tsirkin" , linux-kernel@vger.kernel.org Cc: netdev@vger.kernel.org, John Fastabend , David Miller References: <1516923320-16959-1-git-send-email-mst@redhat.com> <1516923320-16959-10-git-send-email-mst@redhat.com> From: Jason Wang Message-ID: <1a069bf6-176c-375a-75fb-6cd9f5f9883b@redhat.com> Date: Fri, 26 Jan 2018 10:38:12 +0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.5.0 MIME-Version: 1.0 In-Reply-To: <1516923320-16959-10-git-send-email-mst@redhat.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2018年01月26日 07:36, Michael S. Tsirkin wrote: > In theory compiler could tear queue loads or stores in two. It does not > seem to be happening in practice but it seems easier to convert the > cases where this would be a problem to READ/WRITE_ONCE than worry about > it. > > Signed-off-by: Michael S. Tsirkin > --- > include/linux/ptr_ring.h | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/include/linux/ptr_ring.h b/include/linux/ptr_ring.h > index 3a19ebd..1883d61 100644 > --- a/include/linux/ptr_ring.h > +++ b/include/linux/ptr_ring.h > @@ -114,7 +114,7 @@ static inline int __ptr_ring_produce(struct ptr_ring *r, void *ptr) > /* Pairs with smp_read_barrier_depends in __ptr_ring_consume. */ > smp_wmb(); > > - r->queue[r->producer++] = ptr; > + WRITE_ONCE(r->queue[r->producer++], ptr); > if (unlikely(r->producer >= r->size)) > r->producer = 0; You may want WRITE_ONCE() here? And if we just fix the out of bound r->producer, we may just need one WRITE_ONCE(). Thanks > return 0; > @@ -173,7 +173,7 @@ static inline int ptr_ring_produce_bh(struct ptr_ring *r, void *ptr) > static inline void *__ptr_ring_peek(struct ptr_ring *r) > { > if (likely(r->size)) > - return r->queue[r->consumer_head]; > + return READ_ONCE(r->queue[r->consumer_head]); > return NULL; > } >