From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752297AbcHKKjj (ORCPT ); Thu, 11 Aug 2016 06:39:39 -0400 Received: from mail-wm0-f65.google.com ([74.125.82.65]:35574 "EHLO mail-wm0-f65.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751062AbcHKKjh (ORCPT ); Thu, 11 Aug 2016 06:39:37 -0400 Date: Thu, 11 Aug 2016 12:38:59 +0200 From: Daniel Vetter To: Johannes Berg Cc: linux-kernel@vger.kernel.org, Johannes Berg , Peter Zijlstra , intel-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org, Daniel Vetter , "Paul E . McKenney" , Ingo Molnar Subject: Re: [PATCH 1/2] Revert "drm/fb-helper: Reduce READ_ONCE(master) to lockless_dereference" Message-ID: <20160811103859.GL6232@phenom.ffwll.local> Mail-Followup-To: Johannes Berg , linux-kernel@vger.kernel.org, Johannes Berg , Peter Zijlstra , intel-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org, Daniel Vetter , "Paul E . McKenney" , Ingo Molnar References: <1470909022-687-1-git-send-email-johannes@sipsolutions.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1470909022-687-1-git-send-email-johannes@sipsolutions.net> X-Operating-System: Linux phenom 4.6.0-1-amd64 User-Agent: Mutt/1.6.0 (2016-04-01) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Aug 11, 2016 at 11:50:21AM +0200, Johannes Berg wrote: > From: Johannes Berg > > This reverts commit fa7d81bb3c269a2ee38b6e4d569d9eb8be1a78ad. > > As Peter explained: > [...] lockless_dereference() is _stronger_ than READ_ONCE(), not weaker. > > [...] > > Also, clue is in the name: 'dereference', you don't actually dereference > the pointer here, only load it. > > My next patch breaks compile on this, because it assumes you want to > deference and thus also need the struct type visible (which it isn't > here), so revert it. > > Cc: Peter Zijlstra > Signed-off-by: Johannes Berg Reviewed-by: Daniel Vetter And ack-by: me for merging through whatever tree this makes sense for. -Daniel > --- > drivers/gpu/drm/drm_fb_helper.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/drivers/gpu/drm/drm_fb_helper.c b/drivers/gpu/drm/drm_fb_helper.c > index ce54e985d91b..0a06f9120b5a 100644 > --- a/drivers/gpu/drm/drm_fb_helper.c > +++ b/drivers/gpu/drm/drm_fb_helper.c > @@ -464,7 +464,7 @@ static bool drm_fb_helper_is_bound(struct drm_fb_helper *fb_helper) > > /* Sometimes user space wants everything disabled, so don't steal the > * display if there's a master. */ > - if (lockless_dereference(dev->master)) > + if (READ_ONCE(dev->master)) > return false; > > drm_for_each_crtc(crtc, dev) { > -- > 2.8.1 > > _______________________________________________ > dri-devel mailing list > dri-devel@lists.freedesktop.org > https://lists.freedesktop.org/mailman/listinfo/dri-devel -- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch