From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752939AbcFJHDR (ORCPT ); Fri, 10 Jun 2016 03:03:17 -0400 Received: from mx1.redhat.com ([209.132.183.28]:57071 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751017AbcFJHDQ (ORCPT ); Fri, 10 Jun 2016 03:03:16 -0400 Date: Fri, 10 Jun 2016 09:03:10 +0200 From: Oleg Nesterov To: Andrea Parri Cc: Peter Zijlstra , LKML Subject: Re: [PATCH] events/uprobes: move smp_read_barrier_depends() where needed Message-ID: <20160610070310.GA6843@redhat.com> References: <1465496321-10898-1-git-send-email-parri.andrea@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1465496321-10898-1-git-send-email-parri.andrea@gmail.com> User-Agent: Mutt/1.5.24 (2015-08-30) X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.29]); Fri, 10 Jun 2016 07:03:16 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 06/09, Andrea Parri wrote: > > There is no need to use the barrier if there is no dereference/ > memory access; move it where needed (currently, affecting only > Alpha). OK, although area == NULL is unlikely case, > While touching this, also make the reads _ONCE(). Why? both xol_area/vaddr can't change. > Signed-off-by: Andrea Parri > --- > kernel/events/uprobes.c | 9 +++++---- > 1 file changed, 5 insertions(+), 4 deletions(-) > > diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c > index b7a525ab2083..b1364acd683e 100644 > --- a/kernel/events/uprobes.c > +++ b/kernel/events/uprobes.c > @@ -1520,10 +1520,11 @@ static unsigned long get_trampoline_vaddr(void) > struct xol_area *area; > unsigned long trampoline_vaddr = -1; > > - area = current->mm->uprobes_state.xol_area; > - smp_read_barrier_depends(); > - if (area) > - trampoline_vaddr = area->vaddr; > + area = READ_ONCE(current->mm->uprobes_state.xol_area); > + if (area) { > + smp_read_barrier_depends(); > + trampoline_vaddr = READ_ONCE(area->vaddr); > + } > > return trampoline_vaddr; > } > -- > 1.9.1 >