From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751633AbdF1LK5 (ORCPT ); Wed, 28 Jun 2017 07:10:57 -0400 Received: from Galois.linutronix.de ([146.0.238.70]:50494 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751567AbdF1LKt (ORCPT ); Wed, 28 Jun 2017 07:10:49 -0400 Date: Wed, 28 Jun 2017 13:10:14 +0200 (CEST) From: Thomas Gleixner To: Dmitry Vyukov cc: Sebastian Andrzej Siewior , Ingo Molnar , Mark Rutland , Peter Zijlstra , Will Deacon , "H. Peter Anvin" , Andrey Ryabinin , kasan-dev , "x86@kernel.org" , LKML , Andrew Morton , "linux-mm@kvack.org" , Linus Torvalds Subject: Re: [PATCH] locking/atomics: don't alias ____ptr In-Reply-To: Message-ID: References: <85d51d3551b676ba1fc40e8fbddd2eadd056d8dd.1498140838.git.dvyukov@google.com> <20170628100246.7nsvhblgi3xjbc4m@breakpoint.cc> User-Agent: Alpine 2.20 (DEB 67 2015-01-07) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 28 Jun 2017, Dmitry Vyukov wrote: > On Wed, Jun 28, 2017 at 12:02 PM, Sebastian Andrzej Siewior wrote: > > @@ -359,16 +359,16 @@ static __always_inline bool atomic64_add_negative(s64 i, atomic64_t *v) > > > > #define cmpxchg64(ptr, old, new) \ > > ({ \ > > - __typeof__(ptr) ____ptr = (ptr); \ > > - kasan_check_write(____ptr, sizeof(*____ptr)); \ > > - arch_cmpxchg64(____ptr, (old), (new)); \ > > + __typeof__(ptr) ____ptr64 = (ptr); \ > > + kasan_check_write(____ptr64, sizeof(*____ptr64));\ > > + arch_cmpxchg64(____ptr64, (old), (new)); \ > > }) > > > > #define cmpxchg64_local(ptr, old, new) \ > > ({ \ > > - __typeof__(ptr) ____ptr = (ptr); \ > > - kasan_check_write(____ptr, sizeof(*____ptr)); \ > > - arch_cmpxchg64_local(____ptr, (old), (new)); \ > > + __typeof__(ptr) ____ptr64 = (ptr); \ > > + kasan_check_write(____ptr64, sizeof(*____ptr64));\ > > + arch_cmpxchg64_local(____ptr64, (old), (new)); \ > > }) > > > > #define cmpxchg_double(p1, p2, o1, o2, n1, n2) \ > > > Doh! Thanks for fixing this. I think I've a similar crash in a > different place when I developed the patch. > The problem is that when we do: > > __typeof__(ptr) ____ptr = (ptr); \ > arch_cmpxchg64_local(____ptr, (old), (new)); \ > > We don't necessary pass value of our just declared ____ptr to > arch_cmpxchg64_local(). We just pass a symbolic identifier. So if > arch_cmpxchg64_local() declares own ____ptr and then tries to use what > we passed ("____ptr") it will actually refer to own variable declared > rather than to what we wanted to pass in. > > In my case I ended up with something like: > > __typeof__(foo) __ptr = __ptr; > > which compiler decided to turn into 0. > > Thank you, macros. > > We can add more underscores, but the problem can happen again. Should > we prefix current function/macro name to all local vars?.. Actually we can void that ___ptr dance completely. Thanks, tglx 8<-------------------- --- a/include/asm-generic/atomic-instrumented.h +++ b/include/asm-generic/atomic-instrumented.h @@ -359,37 +359,32 @@ static __always_inline bool atomic64_add #define cmpxchg(ptr, old, new) \ ({ \ - __typeof__(ptr) ___ptr = (ptr); \ - kasan_check_write(___ptr, sizeof(*___ptr)); \ + kasan_check_write((ptr), sizeof(*(ptr))); \ arch_cmpxchg((ptr), (old), (new)); \ }) #define sync_cmpxchg(ptr, old, new) \ ({ \ - __typeof__(ptr) ___ptr = (ptr); \ - kasan_check_write(___ptr, sizeof(*___ptr)); \ - arch_sync_cmpxchg(___ptr, (old), (new)); \ + kasan_check_write((ptr), sizeof(*(ptr))); \ + arch_sync_cmpxchg((ptr), (old), (new)); \ }) #define cmpxchg_local(ptr, old, new) \ ({ \ - __typeof__(ptr) ____ptr = (ptr); \ - kasan_check_write(____ptr, sizeof(*____ptr)); \ - arch_cmpxchg_local(____ptr, (old), (new)); \ + kasan_check_write((ptr), sizeof(*(ptr))); \ + arch_cmpxchg_local((ptr), (old), (new)); \ }) #define cmpxchg64(ptr, old, new) \ ({ \ - __typeof__(ptr) ____ptr = (ptr); \ - kasan_check_write(____ptr, sizeof(*____ptr)); \ - arch_cmpxchg64(____ptr, (old), (new)); \ + kasan_check_write((ptr), sizeof(*(ptr))); \ + arch_cmpxchg64((ptr), (old), (new)); \ }) #define cmpxchg64_local(ptr, old, new) \ ({ \ - __typeof__(ptr) ____ptr = (ptr); \ - kasan_check_write(____ptr, sizeof(*____ptr)); \ - arch_cmpxchg64_local(____ptr, (old), (new)); \ + kasan_check_write((ptr), sizeof(*(ptr))); \ + arch_cmpxchg64_local((ptr), (old), (new)); \ }) /*