From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753937AbcCUITM (ORCPT ); Mon, 21 Mar 2016 04:19:12 -0400 Received: from mx1.redhat.com ([209.132.183.28]:38468 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752036AbcCUITG (ORCPT ); Mon, 21 Mar 2016 04:19:06 -0400 From: Vitaly Kuznetsov To: "K. Y. Srinivasan" Cc: gregkh@linuxfoundation.org, linux-kernel@vger.kernel.org, devel@linuxdriverproject.org, olaf@aepfle.de, apw@canonical.com, jasowang@redhat.com, stable@vger.kernel.org Subject: Re: [PATCH 3/5] Drivers: hv: vmbus: Fix a bug in hv_need_to_signal_on_read() References: <1458350038-32624-1-git-send-email-kys@microsoft.com> <1458350065-32666-1-git-send-email-kys@microsoft.com> <1458350065-32666-3-git-send-email-kys@microsoft.com> Date: Mon, 21 Mar 2016 09:19:01 +0100 In-Reply-To: <1458350065-32666-3-git-send-email-kys@microsoft.com> (K. Y. Srinivasan's message of "Fri, 18 Mar 2016 18:14:23 -0700") Message-ID: <87shzk1bwq.fsf@vitty.brq.redhat.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/24.5 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org "K. Y. Srinivasan" writes: > We need to issue a full memory barrier prior making a signalling > decision. Any reason this should be mb()? This is pretty strong and will probably lead to performace regression ... and, btw, we have another mb() in hv_ringbuffer_read(). Could you please describe the scenarion you're trying to protect against so we could search for a better solution? > > Signed-off-by: K. Y. Srinivasan > Cc: stable@vger.kernel.org > --- > drivers/hv/ring_buffer.c | 1 + > 1 files changed, 1 insertions(+), 0 deletions(-) > > diff --git a/drivers/hv/ring_buffer.c b/drivers/hv/ring_buffer.c > index 2919395..67dc245 100644 > --- a/drivers/hv/ring_buffer.c > +++ b/drivers/hv/ring_buffer.c > @@ -104,6 +104,7 @@ static bool hv_need_to_signal_on_read(struct hv_ring_buffer_info *rbi) > u32 cur_write_sz; > u32 pending_sz; > > + mb(); > pending_sz = READ_ONCE(rbi->ring_buffer->pending_send_sz); > /* If the other end is not blocked on write don't bother. */ > if (pending_sz == 0) -- Vitaly