From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754246AbcHSGnT (ORCPT ); Fri, 19 Aug 2016 02:43:19 -0400 Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:42795 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753022AbcHSGnS (ORCPT ); Fri, 19 Aug 2016 02:43:18 -0400 X-IBM-Helo: d03dlp03.boulder.ibm.com X-IBM-MailFrom: paulmck@linux.vnet.ibm.com Date: Thu, 18 Aug 2016 14:02:13 -0700 From: "Paul E. McKenney" To: eric.dumazet@gmail.com, peterz@infradead.org, linux-kernel@vger.kernel.org Subject: Fw: [GIT PULL] locking fixes Reply-To: paulmck@linux.vnet.ibm.com MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-GCONF: 00 X-Content-Scanned: Fidelis XPS MAILER x-cbid: 16081821-0016-0000-0000-000004753849 X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00005613; HX=3.00000240; KW=3.00000007; PH=3.00000004; SC=3.00000181; SDB=6.00746554; UDB=6.00351988; IPR=6.00519088; BA=6.00004668; NDR=6.00000001; ZLA=6.00000005; ZF=6.00000009; ZB=6.00000000; ZP=6.00000000; ZH=6.00000000; ZU=6.00000002; MB=3.00012381; XFM=3.00000011; UTC=2016-08-18 21:02:05 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 16081821-0017-0000-0000-0000322332CA Message-Id: <20160818210213.GB3482@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2016-08-18_09:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 suspectscore=0 malwarescore=0 phishscore=0 adultscore=0 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1604210000 definitions=main-1608180273 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hello, Eric, Does Johannes's recent change to lockless_dereference() help with the sparse issue? Thanx, Paul ----- Forwarded message from Ingo Molnar ----- Date: Thu, 18 Aug 2016 22:34:21 +0200 From: Ingo Molnar To: Linus Torvalds Cc: linux-kernel@vger.kernel.org, Peter Zijlstra , Thomas Gleixner , Andrew Morton , "Paul E. McKenney" Subject: [GIT PULL] locking fixes Linus, Please pull the latest locking-urgent-for-linus git tree from: git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git locking-urgent-for-linus # HEAD: 112dc0c8069e5554e0ad29c58228f1e6ca49e13d locking/barriers: Suppress sparse warnings in lockless_dereference() Two lockless_dereference() related fixes. Thanks, Ingo ------------------> Johannes Berg (2): Revert "drm/fb-helper: Reduce READ_ONCE(master) to lockless_dereference" locking/barriers: Suppress sparse warnings in lockless_dereference() drivers/gpu/drm/drm_fb_helper.c | 2 +- include/linux/compiler.h | 6 +++--- 2 files changed, 4 insertions(+), 4 deletions(-) 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) { diff --git a/include/linux/compiler.h b/include/linux/compiler.h index 1bb954842725..436aa4e42221 100644 --- a/include/linux/compiler.h +++ b/include/linux/compiler.h @@ -527,13 +527,13 @@ static __always_inline void __write_once_size(volatile void *p, void *res, int s * object's lifetime is managed by something other than RCU. That * "something other" might be reference counting or simple immortality. * - * The seemingly unused void * variable is to validate @p is indeed a pointer - * type. All pointer types silently cast to void *. + * The seemingly unused size_t variable is to validate @p is indeed a pointer + * type by making sure it can be dereferenced. */ #define lockless_dereference(p) \ ({ \ typeof(p) _________p1 = READ_ONCE(p); \ - __maybe_unused const void * const _________p2 = _________p1; \ + size_t __maybe_unused __size_of_ptr = sizeof(*(p)); \ smp_read_barrier_depends(); /* Dependency order vs. p above. */ \ (_________p1); \ }) ----- End forwarded message -----