From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754547AbdFWOGZ (ORCPT ); Fri, 23 Jun 2017 10:06:25 -0400 Received: from terminus.zytor.com ([65.50.211.136]:32915 "EHLO terminus.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753611AbdFWOGX (ORCPT ); Fri, 23 Jun 2017 10:06:23 -0400 Date: Fri, 23 Jun 2017 07:01:36 -0700 From: tip-bot for Dmitry Vyukov Message-ID: Cc: mark.rutland@arm.com, tglx@linutronix.de, aryabinin@virtuozzo.com, linux-kernel@vger.kernel.org, akpm@linux-foundation.org, mingo@kernel.org, hpa@zytor.com, dvyukov@google.com, torvalds@linux-foundation.org, will.deacon@arm.com, peterz@infradead.org Reply-To: torvalds@linux-foundation.org, dvyukov@google.com, tglx@linutronix.de, mark.rutland@arm.com, hpa@zytor.com, akpm@linux-foundation.org, mingo@kernel.org, aryabinin@virtuozzo.com, linux-kernel@vger.kernel.org, peterz@infradead.org, will.deacon@arm.com In-Reply-To: <65058e2d09cf0920769ca72a932d9de4f613249d.1498140838.git.dvyukov@google.com> References: <65058e2d09cf0920769ca72a932d9de4f613249d.1498140838.git.dvyukov@google.com> To: linux-tip-commits@vger.kernel.org Subject: [tip:locking/core] locking/atomic/x86, asm-generic: Add comments for atomic instrumentation Git-Commit-ID: 3f04aae282662e4075b6c3824aa3e1e1dabacd31 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: 3f04aae282662e4075b6c3824aa3e1e1dabacd31 Gitweb: http://git.kernel.org/tip/3f04aae282662e4075b6c3824aa3e1e1dabacd31 Author: Dmitry Vyukov AuthorDate: Thu, 22 Jun 2017 16:14:19 +0200 Committer: Ingo Molnar CommitDate: Fri, 23 Jun 2017 10:50:20 +0200 locking/atomic/x86, asm-generic: Add comments for atomic instrumentation The comments are factored out from the code changes to make them easier to read. Add them separately to explain some non-obvious aspects. Signed-off-by: Dmitry Vyukov Reviewed-by: Andrey Ryabinin Acked-by: Mark Rutland Cc: Andrew Morton Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: Will Deacon Cc: kasan-dev@googlegroups.com Cc: linux-mm@kvack.org Link: http://lkml.kernel.org/r/65058e2d09cf0920769ca72a932d9de4f613249d.1498140838.git.dvyukov@google.com Signed-off-by: Ingo Molnar --- arch/x86/include/asm/atomic.h | 4 ++++ include/asm-generic/atomic-instrumented.h | 30 ++++++++++++++++++++++++++++++ 2 files changed, 34 insertions(+) diff --git a/arch/x86/include/asm/atomic.h b/arch/x86/include/asm/atomic.h index 03dd2a6..b1cd05d 100644 --- a/arch/x86/include/asm/atomic.h +++ b/arch/x86/include/asm/atomic.h @@ -23,6 +23,10 @@ */ static __always_inline int arch_atomic_read(const atomic_t *v) { + /* + * Note for KASAN: we deliberately don't use READ_ONCE_NOCHECK() here, + * it's non-inlined function that increases binary size and stack usage. + */ return READ_ONCE((v)->counter); } diff --git a/include/asm-generic/atomic-instrumented.h b/include/asm-generic/atomic-instrumented.h index a0f5b75..5771439 100644 --- a/include/asm-generic/atomic-instrumented.h +++ b/include/asm-generic/atomic-instrumented.h @@ -1,3 +1,15 @@ +/* + * This file provides wrappers with KASAN instrumentation for atomic operations. + * To use this functionality an arch's atomic.h file needs to define all + * atomic operations with arch_ prefix (e.g. arch_atomic_read()) and include + * this file at the end. This file provides atomic_read() that forwards to + * arch_atomic_read() for actual atomic operation. + * Note: if an arch atomic operation is implemented by means of other atomic + * operations (e.g. atomic_read()/atomic_cmpxchg() loop), then it needs to use + * arch_ variants (i.e. arch_atomic_read()/arch_atomic_cmpxchg()) to avoid + * double instrumentation. + */ + #ifndef _LINUX_ATOMIC_INSTRUMENTED_H #define _LINUX_ATOMIC_INSTRUMENTED_H @@ -336,6 +348,15 @@ static __always_inline bool atomic64_add_negative(s64 i, atomic64_t *v) return arch_atomic64_add_negative(i, v); } +/* + * In the following macros we need to be careful to not clash with arch_ macros. + * arch_xchg() can be defined as an extended statement expression as well, + * if we define a __ptr variable, and arch_xchg() also defines __ptr variable, + * and we pass __ptr as an argument to arch_xchg(), it will use own __ptr + * instead of ours. This leads to unpleasant crashes. To avoid the problem + * the following macros declare variables with lots of underscores. + */ + #define cmpxchg(ptr, old, new) \ ({ \ __typeof__(ptr) ___ptr = (ptr); \ @@ -371,6 +392,15 @@ static __always_inline bool atomic64_add_negative(s64 i, atomic64_t *v) arch_cmpxchg64_local(____ptr, (old), (new)); \ }) +/* + * Originally we had the following code here: + * __typeof__(p1) ____p1 = (p1); + * kasan_check_write(____p1, 2 * sizeof(*____p1)); + * arch_cmpxchg_double(____p1, (p2), (o1), (o2), (n1), (n2)); + * But it leads to compilation failures (see gcc issue 72873). + * So for now it's left non-instrumented. + * There are few callers of cmpxchg_double(), so it's not critical. + */ #define cmpxchg_double(p1, p2, o1, o2, n1, n2) \ ({ \ arch_cmpxchg_double((p1), (p2), (o1), (o2), (n1), (n2)); \