From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753430AbcFJM00 (ORCPT ); Fri, 10 Jun 2016 08:26:26 -0400 Received: from mx1.redhat.com ([209.132.183.28]:59377 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752785AbcFJM0Y (ORCPT ); Fri, 10 Jun 2016 08:26:24 -0400 Date: Fri, 10 Jun 2016 14:26:18 +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: <20160610122537.GA7776@redhat.com> References: <1465496321-10898-1-git-send-email-parri.andrea@gmail.com> <20160610070310.GA6843@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20160610070310.GA6843@redhat.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 [10.5.110.38]); Fri, 10 Jun 2016 12:26:23 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 06/10, Oleg Nesterov wrote: > > 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. and perhaps it would be better to eliminate this smp_read_barrier_depends() altogether, we have a lot of helpers. I mean, static unsigned long get_trampoline_vaddr(void) { struct xol_area *area; area = lockless_dereference(current->mm->uprobes_state.xol_area); if (area) return area->vaddr; return -1; } looks a bit more simple/clean. Note also another smp_read_barrier_depends() in get_xol_area() which can be changed the same way. What do you think? Oleg.