From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1947058AbcHRLAh (ORCPT ); Thu, 18 Aug 2016 07:00:37 -0400 Received: from terminus.zytor.com ([198.137.202.10]:58414 "EHLO terminus.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1945998AbcHRLAf (ORCPT ); Thu, 18 Aug 2016 07:00:35 -0400 Date: Thu, 18 Aug 2016 03:59:35 -0700 From: tip-bot for Johannes Berg Message-ID: Cc: peterz@infradead.org, paulmck@linux.vnet.ibm.com, mingo@kernel.org, tglx@linutronix.de, chris@chris-wilson.co.uk, akpm@linux-foundation.org, hpa@zytor.com, johannes.berg@intel.com, torvalds@linux-foundation.org, linux-kernel@vger.kernel.org, daniel.vetter@ffwll.ch Reply-To: daniel.vetter@ffwll.ch, linux-kernel@vger.kernel.org, torvalds@linux-foundation.org, hpa@zytor.com, johannes.berg@intel.com, chris@chris-wilson.co.uk, tglx@linutronix.de, akpm@linux-foundation.org, mingo@kernel.org, paulmck@linux.vnet.ibm.com, peterz@infradead.org In-Reply-To: <1470909022-687-1-git-send-email-johannes@sipsolutions.net> References: <1470909022-687-1-git-send-email-johannes@sipsolutions.net> To: linux-tip-commits@vger.kernel.org Subject: [tip:locking/core] Revert "drm/fb-helper: Reduce READ_ONCE(master) to lockless_dereference" Git-Commit-ID: 8180cfb96098f7066fbd0a44ac3aaf422f74609d X-Mailer: tip-git-log-daemon Robot-ID: Robot-Unsubscribe: Contact to get blacklisted from these emails MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Content-Type: text/plain; charset=UTF-8 Content-Disposition: inline Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Commit-ID: 8180cfb96098f7066fbd0a44ac3aaf422f74609d Gitweb: http://git.kernel.org/tip/8180cfb96098f7066fbd0a44ac3aaf422f74609d Author: Johannes Berg AuthorDate: Thu, 11 Aug 2016 11:50:21 +0200 Committer: Ingo Molnar CommitDate: Thu, 18 Aug 2016 11:34:26 +0200 Revert "drm/fb-helper: Reduce READ_ONCE(master) to lockless_dereference" This reverts commit: fa7d81bb3c269 ("drm/fb-helper: Reduce READ_ONCE(master) to lockless_dereference") 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 the compile without this revert, because it assumes you want to deference and thus also need the struct type visible (which it isn't here), so revert it. Tested-by: Paul E. McKenney Signed-off-by: Johannes Berg Signed-off-by: Peter Zijlstra (Intel) Reviewed-by: Daniel Vetter Cc: Andrew Morton Cc: Chris Wilson Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Link: http://lkml.kernel.org/r/1470909022-687-1-git-send-email-johannes@sipsolutions.net Signed-off-by: Ingo Molnar --- 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 ce54e98..0a06f91 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) {