linux-kernel - Re: [PATCH] kmemleak: Do not enable KMEMCHECK_PARTIAL_OK if DEBUG

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Message-ID: <4B5FDD85.5080701@cs.helsinki.fi>
Date:	Wed, 27 Jan 2010 08:30:29 +0200
From:	Pekka Enberg <penberg@...helsinki.fi>
To:	Catalin Marinas <catalin.marinas@....com>
CC:	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Christian Casteyde <casteyde.christian@...e.fr>,
	vegard.nossum@...il.com
Subject: Re: [PATCH] kmemleak: Do not enable KMEMCHECK_PARTIAL_OK if DEBUG_KMEMLEAK

Hi Catalin,

Catalin Marinas kirjoitti:
> This is a fix for bug #14845 (bugzilla.kernel.org). The
> update_checksum() function in mm/kmemleak.c calls
> kmemcheck_is_obj_initialised() before scanning an object. When
> KMEMCHECK_PARTIAL_OK is enabled, this function returns true. However,
> the crc32_le() reads smaller intervals (32-bit) for which
> kmemleak_is_obj_initialised() is may be false leading to a kmemcheck
> warning.
> 
> Signed-off-by: Catalin Marinas <catalin.marinas@....com>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: Christian Casteyde <casteyde.christian@...e.fr>
> Cc: Pekka Enberg <penberg@...helsinki.fi>
> ---
>  lib/Kconfig.kmemcheck |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
> 
> diff --git a/lib/Kconfig.kmemcheck b/lib/Kconfig.kmemcheck
> index 846e039..80660e9 100644
> --- a/lib/Kconfig.kmemcheck
> +++ b/lib/Kconfig.kmemcheck
> @@ -75,7 +75,7 @@ config KMEMCHECK_SHADOW_COPY_SHIFT
>  config KMEMCHECK_PARTIAL_OK
>  	bool "kmemcheck: allow partially uninitialized memory"
>  	depends on KMEMCHECK
> -	default y
> +	default y if !DEBUG_KMEMLEAK
>  	help
>  	  This option works around certain GCC optimizations that produce
>  	  32-bit reads from 16-bit variables where the upper 16 bits are
> 

Disabling KMEMCHECK_PARTIAL_OK can cause other false positives so maybe 
we should add a new function to kmemcheck for kmemleak that only reads 
full intervals?
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