Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1761996AbZD3KNm (ORCPT ); Thu, 30 Apr 2009 06:13:42 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754294AbZD3KNd (ORCPT ); Thu, 30 Apr 2009 06:13:33 -0400 Received: from cantor2.suse.de ([195.135.220.15]:45256 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753616AbZD3KNc (ORCPT ); Thu, 30 Apr 2009 06:13:32 -0400 From: Nikanth Karthikesan Organization: Novell To: Ingo Molnar Subject: Re: [PATCH] Detect and warn on atomic_inc/atomic_dec wrapping around Date: Thu, 30 Apr 2009 15:41:10 +0530 User-Agent: KMail/1.11.1 (Linux/2.6.27.21-0.1-default; KDE/4.2.1; x86_64; ; ) Cc: Andrew Morton , Jens Axboe , linux-kernel@vger.kernel.org References: <200904291221.40361.knikanth@novell.com> <200904301259.11413.knikanth@novell.com> <20090430082350.GA21699@elte.hu> In-Reply-To: <20090430082350.GA21699@elte.hu> MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Content-Disposition: inline Message-Id: <200904301541.11264.knikanth@novell.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 5908 Lines: 203 On Thursday 30 April 2009 13:53:50 Ingo Molnar wrote: > * Nikanth Karthikesan wrote: > > Add a debug option to detect and warn when the 32-bit atomic_t > > wraps around during atomic_inc and atomic_dec. > > > > Signed-off-by: Nikanth Karthikesan > > hm, what's the motivation? > See http://lkml.org/lkml/2009/4/29/424 Andrew said that a generic atomic_t overflow checker might be useful. > As a generic debug helper this is not appropriate i think - counts > can easily have a meaning when going negative as well. (we have no > signed-atomic primitives) > This doesn't warn when it becomes negative/positive from zero, but only when it wraps around^W^Woverflows, trying to add past INT_MAX or subtract from INT_MIN. > > static inline void atomic_inc(atomic_t *v) > > { > > +#if defined(CONFIG_ENABLE_WARN_ATOMIC_INC_WRAP) > > + WARN_ON(atomic_add_unless(v, 1, INT_MAX) == 0); > > +#else > > asm volatile(LOCK_PREFIX "incl %0" > > > > : "+m" (v->counter)); > > > > +#endif > > } > > also looks a bit ugly - this ugly #ifdef would spread into every > architecture. > > If we want to restrict atomic_t value ranges like that then the > clean solution would be to add generic wrappers doing the debug > (once, in generic code), and renaming the arch primitives to > raw_atomic_inc() (etc), doing the lowlevel bits cleanly. > Here is a patch which does it this way. Thanks Nikanth 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. 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 7abdaa9..6eda22b 100644 --- a/include/asm-generic/atomic.h +++ b/include/asm-generic/atomic.h @@ -4,15 +4,52 @@ * 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 + +#if defined(CONFIG_ENABLE_WARN_ATOMIC_INC_WRAP) + +/** + * atomic_inc - increment atomic variable + * @v: pointer of type atomic_t + * + * Atomically increments @v by 1. + * Prints a warning if it wraps around. + */ +static inline void atomic_inc(atomic_t *v) +{ + WARN_ON(atomic_add_unless(v, 1, INT_MAX) == 0); +} + +/** + * atomic_dec - decrement atomic variable + * @v: pointer of type atomic_t + * + * Atomically decrements @v by 1. + * Prints a warning if it wraps around. + */ +static inline void atomic_dec(atomic_t *v) +{ + WARN_ON(atomic_add_unless(v, -1, INT_MIN) == 0); +} + +#else + +#define atomic_inc(v) raw_atomic_inc(v) +#define atomic_dec(v) raw_atomic_dec(v) + +#endif + /* * 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..a446a98 100644 --- a/lib/Kconfig.debug +++ b/lib/Kconfig.debug @@ -17,6 +17,13 @@ config ENABLE_WARN_DEPRECATED Disable this to suppress the "warning: 'foo' is deprecated (declared at kernel/power/somefile.c:1234)" messages. +config ENABLE_WARN_ATOMIC_INC_WRAP + bool "Enable warning on atomic_inc()/atomic_dec() wrap" + 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 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/