From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755851AbZEHKp3 (ORCPT ); Fri, 8 May 2009 06:45:29 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752676AbZEHKpU (ORCPT ); Fri, 8 May 2009 06:45:20 -0400 Received: from cantor.suse.de ([195.135.220.2]:57826 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751831AbZEHKpR (ORCPT ); Fri, 8 May 2009 06:45:17 -0400 From: Nikanth Karthikesan Organization: suse.de To: Andrew Morton Subject: Re: [PATCH] Detect and warn on atomic_inc/atomic_dec wrapping around Date: Fri, 8 May 2009 16:16:53 +0530 User-Agent: KMail/1.11.1 (Linux/2.6.27.21-0.1-default; KDE/4.2.1; x86_64; ; ) Cc: mingo@elte.hu, jens.axboe@oracle.com, linux-kernel@vger.kernel.org References: <200904291221.40361.knikanth@novell.com> <20090507172316.20a95642.akpm@linux-foundation.org> <200905081610.50202.knikanth@suse.de> In-Reply-To: <200905081610.50202.knikanth@suse.de> MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Content-Disposition: inline Message-Id: <200905081616.53684.knikanth@suse.de> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Friday 08 May 2009 16:10:49 Nikanth Karthikesan wrote: > On Friday 08 May 2009 05:53:16 Andrew Morton wrote: > > On Thu, 30 Apr 2009 19:39:50 +0530 > > > > Nikanth Karthikesan wrote: > > > Detect and warn on atomic_inc/atomic_dec overflow. > > > > > > Add a debug option to detect and warn when the 32-bit atomic_t > > > overflows during atomic_inc and atomic_dec. > > > > > > > > > ... > > > > > > --- a/include/asm-generic/atomic.h > > > +++ b/include/asm-generic/atomic.h > > > @@ -4,15 +4,51 @@ > > > * Copyright (C) 2005 Silicon Graphics, Inc. > > > * Christoph Lameter > > > * > > > - * Allows to provide arch independent atomic definitions without the > > > need to - * edit all arch specific atomic.h files. > > > */ > > > > > > +#include > > > #include > > > +#include > > > > We're going to have real trouble making changes like this to a > > low-level header file - sparc64 results below. > > > > > +/** > > > + * atomic_inc - increment atomic variable > > > + * @v: pointer of type atomic_t > > > + * > > > + * Atomically increments @v by 1. > > > + */ > > > +static inline void atomic_inc(atomic_t *v) > > > +{ > > > +#ifdef CONFIG_ENABLE_WARN_ATOMIC_INC_WRAP > > > + WARN_ONCE((atomic_read(v) > (INT_MAX / 2)), > > > + KERN_ERR "atomic inc overflow!"); > > > +#endif > > > + raw_atomic_inc(v); > > > +} > > > > Are we allowed to assume that atomic_inc==raw_atomic_inc for all > > architectures which use this definition? > > No. Only for architectures that have HAVE_ARCH_DEBUG_ATOMIC. I missed > enclosing the change with #ifdef HAVE_ARCH_DEBUG_ATOMIC. That should solve > the problem as it wont be built for other architectures at all. > > > Do we know that atomic_read() is defined at this point? > > Yes. > > > We can avoid the problematic includes via > > > > extern void atomic_inc_screwed_up(atomic_t *v); > > This and even having atomic_inc defined as a c function instead of a macro > has a problem. WARN_ONCE would warn only once even if more than 1 variable > wraps around. So should we have atomic_inc itself as a macro instead? > > Also it would report the location in source as include/asm-generic/atomic.h > instead of the caller. But it should be fine as stack trace would be > printed. > > Anyway I have converted warn_once as an extern function. > > Changes from the previous version: > 1. Enclose everything with #ifdef CONFIG_HAVE_ARCH_DEBUG_ATOMIC. > 2. Make the warn_once as an extern function and remove the > #include. This is not required as CONFIG_HAVE_ARCH_DEBUG_ATOMIC > is defined onlf for x86 and it does not have problem with this include. I > think we could remove this and also make everything as macro? > If you think this would be better, here is a patch that does this. Having it as a macro would warn for every variable that could overflow. Thanks Nikanth Subject: atomic: detect and warn on atomic_inc/atomic_dec wrapping around From: Nikanth Karthikesan Add a debug option to detect and warn when the 32-bit atomic_t overflows during atomic_inc and atomic_dec. We expect that overflow and underflow of an atomic_t is usually a bug. There was a patch of this nature in -mm for a long time and it never triggered false positives and it did find a couple of real bugs. The option is default-y for now. It will have a fairly nasty impact on .text size so we may decide to switch it to default-n prior to a kernel release. Signed-off-by: Nikanth Karthikesan Acked-by: Ingo Molnar Signed-off-by: Andrew Morton --- diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig index df9e885..dd49be3 100644 --- a/arch/x86/Kconfig +++ b/arch/x86/Kconfig @@ -46,6 +46,7 @@ config X86 select HAVE_KERNEL_GZIP select HAVE_KERNEL_BZIP2 select HAVE_KERNEL_LZMA + select HAVE_ARCH_DEBUG_ATOMIC config ARCH_DEFCONFIG string diff --git a/arch/x86/include/asm/atomic_32.h b/arch/x86/include/asm/atomic_32.h index 85b46fb..c6a17bb 100644 --- a/arch/x86/include/asm/atomic_32.h +++ b/arch/x86/include/asm/atomic_32.h @@ -78,24 +78,24 @@ static inline int atomic_sub_and_test(int i, atomic_t *v) } /** - * atomic_inc - increment atomic variable + * raw_atomic_inc - increment atomic variable * @v: pointer of type atomic_t * * Atomically increments @v by 1. */ -static inline void atomic_inc(atomic_t *v) +static inline void raw_atomic_inc(atomic_t *v) { asm volatile(LOCK_PREFIX "incl %0" : "+m" (v->counter)); } /** - * atomic_dec - decrement atomic variable + * raw_atomic_dec - decrement atomic variable * @v: pointer of type atomic_t * * Atomically decrements @v by 1. */ -static inline void atomic_dec(atomic_t *v) +static inline void raw_atomic_dec(atomic_t *v) { asm volatile(LOCK_PREFIX "decl %0" : "+m" (v->counter)); diff --git a/arch/x86/include/asm/atomic_64.h b/arch/x86/include/asm/atomic_64.h index 8c21731..1183b85 100644 --- a/arch/x86/include/asm/atomic_64.h +++ b/arch/x86/include/asm/atomic_64.h @@ -77,12 +77,12 @@ static inline int atomic_sub_and_test(int i, atomic_t *v) } /** - * atomic_inc - increment atomic variable + * raw_atomic_inc - increment atomic variable * @v: pointer of type atomic_t * * Atomically increments @v by 1. */ -static inline void atomic_inc(atomic_t *v) +static inline void raw_atomic_inc(atomic_t *v) { asm volatile(LOCK_PREFIX "incl %0" : "=m" (v->counter) @@ -90,12 +90,12 @@ static inline void atomic_inc(atomic_t *v) } /** - * atomic_dec - decrement atomic variable + * raw_atomic_dec - decrement atomic variable * @v: pointer of type atomic_t * * Atomically decrements @v by 1. */ -static inline void atomic_dec(atomic_t *v) +static inline void raw_atomic_dec(atomic_t *v) { asm volatile(LOCK_PREFIX "decl %0" : "=m" (v->counter) diff --git a/include/asm-generic/atomic.h b/include/asm-generic/atomic.h index 3673a13..004b018 100644 --- a/include/asm-generic/atomic.h +++ b/include/asm-generic/atomic.h @@ -4,15 +4,56 @@ * Copyright (C) 2005 Silicon Graphics, Inc. * Christoph Lameter * - * Allows to provide arch independent atomic definitions without the need to - * edit all arch specific atomic.h files. */ #include +#ifdef CONFIG_HAVE_ARCH_DEBUG_ATOMIC + +#include +#include + +#ifdef CONFIG_ENABLE_WARN_ATOMIC_INC_WRAP + +/** + * atomic_inc - increment atomic variable + * @v: pointer of type atomic_t + * + * Atomically increments @v by 1. + */ +#define atomic_inc(v) ({ \ + WARN_ONCE((atomic_read(v) > (INT_MAX / 2)), \ + KERN_ERR "atomic inc overflow!"); \ + raw_atomic_inc(v); \ +}) + +/** + * atomic_dec - decrement atomic variable + * @v: pointer of type atomic_t + * + * Atomically decrements @v by 1. + */ +#define atomic_dec(v) ({ \ + WARN_ONCE((atomic_read(v) < (INT_MIN / 2)), \ + KERN_ERR "atomic dec underflow!"); \ + raw_atomic_dec(v); \ +}) + +#else /* CONFIG_ENABLE_WARN_ATOMIC_INC_WRAP */ + +#define atomic_inc(v) raw_atomic_inc(v) +#define atomic_dec(v) raw_atomic_dec(v) + +#endif /* !CONFIG_ENABLE_WARN_ATOMIC_INC_WRAP */ + +#endif /* CONFIG_HAVE_ARCH_DEBUG_ATOMIC */ + /* * Suppport for atomic_long_t * + * Allows to provide arch independent atomic definitions without the need to + * edit all arch specific atomic.h files. + * * Casts for parameters are avoided for existing atomic functions in order to * avoid issues with cast-as-lval under gcc 4.x and other limitations that the * macros of a platform may have. diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug index 812c282..773c1a4 100644 --- a/lib/Kconfig.debug +++ b/lib/Kconfig.debug @@ -17,6 +17,17 @@ config ENABLE_WARN_DEPRECATED Disable this to suppress the "warning: 'foo' is deprecated (declared at kernel/power/somefile.c:1234)" messages. +config HAVE_ARCH_DEBUG_ATOMIC + bool + +config ENABLE_WARN_ATOMIC_INC_WRAP + bool "Enable warning on atomic_inc()/atomic_dec() wrap" + depends on HAVE_ARCH_DEBUG_ATOMIC + default y + help + Enable printing a warning when atomic_inc() or atomic_dec() + operation wraps around the 32-bit value. + config ENABLE_MUST_CHECK bool "Enable __must_check logic" default y