Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756386AbZD3ML0 (ORCPT ); Thu, 30 Apr 2009 08:11:26 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752649AbZD3MLP (ORCPT ); Thu, 30 Apr 2009 08:11:15 -0400 Received: from cantor.suse.de ([195.135.220.2]:34992 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753837AbZD3MLO (ORCPT ); Thu, 30 Apr 2009 08:11:14 -0400 From: Nikanth Karthikesan Organization: Novell To: Ingo Molnar , Andrew Morton Subject: Re: [PATCH] Detect and warn on atomic_inc/atomic_dec wrapping around Date: Thu, 30 Apr 2009 17:38:54 +0530 User-Agent: KMail/1.11.1 (Linux/2.6.27.21-0.1-default; KDE/4.2.1; x86_64; ; ) Cc: Jens Axboe , linux-kernel@vger.kernel.org References: <200904291221.40361.knikanth@novell.com> <200904301541.11264.knikanth@novell.com> <20090430104729.GB6769@elte.hu> In-Reply-To: <20090430104729.GB6769@elte.hu> MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Content-Disposition: inline Message-Id: <200904301738.55301.knikanth@novell.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 11134 Lines: 396 On Thursday 30 April 2009 16:17:29 Ingo Molnar wrote: > * Nikanth Karthikesan wrote: > > > 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. > > ah! The small difference between INT_MAX and UINT_MAX. > > Sure, this debug check makes a lot of sense. -mm even had such > stuff, many years ago? Never went upstream. > > > > > 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) > > #ifdef 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) > > Please turn these into proper, type aware inline functions. > Ok, done. > > +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. > > + > > this needs HAVE_ARCH_DEBUG_ATOMIC added to arch/x86/Kconfig, and a > depends on HAVE_ARCH_DEBUG_ATOMIC. Otherwise this wont build very > well on non-x86 when enabled, right? > Ok, done. > With those small details fixed: > > Acked-by: Ingo Molnar > > Ingo Here is the patch with all those changes incorporated. 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. Signed-off-by: Nikanth Karthikesan Acked-by: Ingo Molnar --- 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 7abdaa9..9f476d7 100644 --- a/include/asm-generic/atomic.h +++ b/include/asm-generic/atomic.h @@ -4,15 +4,71 @@ * 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 + +/** + * atomic_inc - increment atomic variable + * @v: pointer of type atomic_t + * + * Atomically increments @v by 1. + */ +static inline void atomic_inc(atomic_t *v) +{ + raw_atomic_inc(v); +} + +/** + * atomic_dec - increment atomic variable + * @v: pointer of type atomic_t + * + * Atomically decrements @v by 1. + */ +static inline void atomic_dec(atomic_t *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..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 -- 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/