From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932860AbcIELOY (ORCPT ); Mon, 5 Sep 2016 07:14:24 -0400 Received: from terminus.zytor.com ([198.137.202.10]:35422 "EHLO terminus.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932299AbcIELOV (ORCPT ); Mon, 5 Sep 2016 07:14:21 -0400 Date: Mon, 5 Sep 2016 04:13:30 -0700 From: tip-bot for Johannes Berg Message-ID: Cc: linux-kernel@vger.kernel.org, peterz@infradead.org, hpa@zytor.com, johannes.berg@intel.com, paulmck@linux.vnet.ibm.com, mingo@kernel.org, tglx@linutronix.de, fengguang.wu@intel.com, torvalds@linux-foundation.org Reply-To: johannes.berg@intel.com, mingo@kernel.org, paulmck@linux.vnet.ibm.com, tglx@linutronix.de, fengguang.wu@intel.com, torvalds@linux-foundation.org, linux-kernel@vger.kernel.org, peterz@infradead.org, hpa@zytor.com In-Reply-To: <1472192160-4049-1-git-send-email-johannes@sipsolutions.net> References: <1472192160-4049-1-git-send-email-johannes@sipsolutions.net> To: linux-tip-commits@vger.kernel.org Subject: [tip:locking/urgent] locking/barriers: Don't use sizeof(void) in lockless_dereference() Git-Commit-ID: d7127b5e5fa0551be21b86640f1648b224e36d43 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: d7127b5e5fa0551be21b86640f1648b224e36d43 Gitweb: http://git.kernel.org/tip/d7127b5e5fa0551be21b86640f1648b224e36d43 Author: Johannes Berg AuthorDate: Fri, 26 Aug 2016 08:16:00 +0200 Committer: Ingo Molnar CommitDate: Mon, 5 Sep 2016 11:50:42 +0200 locking/barriers: Don't use sizeof(void) in lockless_dereference() My previous commit: 112dc0c8069e ("locking/barriers: Suppress sparse warnings in lockless_dereference()") caused sparse to complain that (in radix-tree.h) we use sizeof(void) since that rcu_dereference()s a void *. Really, all we need is to have the expression *p in here somewhere to make sure p is a pointer type, and sizeof(*p) was the thing that came to my mind first to make sure that's done without really doing anything at runtime. Another thing I had considered was using typeof(*p), but obviously we can't just declare a typeof(*p) variable either, since that may end up being void. Declaring a variable as typeof(*p)* gets around that, and still checks that typeof(*p) is valid, so do that. This type construction can't be done for _________p1 because that will actually be used and causes sparse address space warnings, so keep a separate unused variable for it. Reported-by: Fengguang Wu Signed-off-by: Johannes Berg Signed-off-by: Peter Zijlstra (Intel) Cc: Linus Torvalds Cc: Paul E . McKenney Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: kbuild-all@01.org Fixes: 112dc0c8069e ("locking/barriers: Suppress sparse warnings in lockless_dereference()") Link: http://lkml.kernel.org/r/1472192160-4049-1-git-send-email-johannes@sipsolutions.net Signed-off-by: Ingo Molnar --- include/linux/compiler.h | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-) diff --git a/include/linux/compiler.h b/include/linux/compiler.h index 436aa4e..6685698 100644 --- a/include/linux/compiler.h +++ b/include/linux/compiler.h @@ -527,13 +527,14 @@ 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 size_t variable is to validate @p is indeed a pointer - * type by making sure it can be dereferenced. + * The seemingly unused variable ___typecheck_p validates that @p is + * indeed a pointer type by using a pointer to typeof(*p) as the type. + * Taking a pointer to typeof(*p) again is needed in case p is void *. */ #define lockless_dereference(p) \ ({ \ typeof(p) _________p1 = READ_ONCE(p); \ - size_t __maybe_unused __size_of_ptr = sizeof(*(p)); \ + typeof(*(p)) *___typecheck_p __maybe_unused; \ smp_read_barrier_depends(); /* Dependency order vs. p above. */ \ (_________p1); \ })