From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wr0-f198.google.com (mail-wr0-f198.google.com [209.85.128.198]) by kanga.kvack.org (Postfix) with ESMTP id 332816B0279 for ; Thu, 22 Jun 2017 10:14:27 -0400 (EDT) Received: by mail-wr0-f198.google.com with SMTP id f49so4980629wrf.5 for ; Thu, 22 Jun 2017 07:14:27 -0700 (PDT) Received: from mail-wr0-x230.google.com (mail-wr0-x230.google.com. [2a00:1450:400c:c0c::230]) by mx.google.com with ESMTPS id v2si1697866wrb.15.2017.06.22.07.14.25 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 22 Jun 2017 07:14:25 -0700 (PDT) Received: by mail-wr0-x230.google.com with SMTP id k67so25191954wrc.2 for ; Thu, 22 Jun 2017 07:14:25 -0700 (PDT) From: Dmitry Vyukov Subject: [PATCH v5 4/4] asm-generic, x86: add comments for atomic instrumentation Date: Thu, 22 Jun 2017 16:14:19 +0200 Message-Id: <65058e2d09cf0920769ca72a932d9de4f613249d.1498140838.git.dvyukov@google.com> In-Reply-To: References: In-Reply-To: References: Sender: owner-linux-mm@kvack.org List-ID: To: mark.rutland@arm.com, peterz@infradead.org, mingo@redhat.com, will.deacon@arm.com, hpa@zytor.com, aryabinin@virtuozzo.com, kasan-dev@googlegroups.com, x86@kernel.org, linux-kernel@vger.kernel.org Cc: Dmitry Vyukov , Andrew Morton , linux-mm@kvack.org 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 Acked-by: Mark Rutland Reviewed-by: Andrey Ryabinin Cc: Peter Zijlstra Cc: Will Deacon Cc: Andrew Morton Cc: Ingo Molnar Cc: kasan-dev@googlegroups.com Cc: linux-mm@kvack.org Cc: linux-kernel@vger.kernel.org Cc: x86@kernel.org --- Changes since v3: - rephrase comment in arch_atomic_read() --- 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 03dd2a6cf7e2..b1cd05da5d8a 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 a0f5b7525bb2..5771439e7a31 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)); \ -- 2.13.1.611.g7e3b11ae1-goog -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org