From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753949AbdFSKzC (ORCPT ); Mon, 19 Jun 2017 06:55:02 -0400 Received: from foss.arm.com ([217.140.101.70]:48560 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753580AbdFSKzA (ORCPT ); Mon, 19 Jun 2017 06:55:00 -0400 Date: Mon, 19 Jun 2017 11:54:11 +0100 From: Mark Rutland To: Dmitry Vyukov Cc: 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, Andrew Morton , linux-mm@kvack.org Subject: Re: [PATCH v4 7/7] asm-generic, x86: add comments for atomic instrumentation Message-ID: <20170619105410.GG10246@leverpostej> References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, Jun 17, 2017 at 11:15:33AM +0200, Dmitry Vyukov wrote: > 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 > Cc: Mark Rutland > Cc: Peter Zijlstra > Cc: Will Deacon > Cc: Andrew Morton > Cc: Andrey Ryabinin > Cc: Ingo Molnar > Cc: kasan-dev@googlegroups.com > Cc: linux-mm@kvack.org > Cc: linux-kernel@vger.kernel.org > Cc: x86@kernel.org > The comments look sane to me. When arm64 support comes round, it would be nice to instrument cmpxchg_double(), since I think we're not affected by the compiler issue. We can solve that as and when. FWIW: Acked-by: Mark Rutland Mark. > --- > > 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 304f4f676cce..219c49b4d3aa 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)); \ > -- > 2.13.1.518.g3df882009-goog >