linux-kernel - Re: [PATCH] slub: fix check

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Message-ID: <1312859440.2531.20.camel@edumazet-laptop>
Date:	Tue, 09 Aug 2011 05:10:40 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Akinobu Mita <akinobu.mita@...il.com>
Cc:	linux-kernel@...r.kernel.org,
	Christoph Lameter <cl@...ux-foundation.org>,
	Pekka Enberg <penberg@...nel.org>,
	Matt Mackall <mpm@...enic.com>, linux-mm@...ck.org
Subject: Re: [PATCH] slub: fix check_bytes() for slub debugging

Le dimanche 07 août 2011 à 18:30 +0900, Akinobu Mita a écrit :
> The check_bytes() function is used by slub debugging.  It returns a pointer
> to the first unmatching byte for a character in the given memory area.
> 
> If the character for matching byte is greater than 0x80, check_bytes()
> doesn't work.  Becuase 64-bit pattern is generated as below.
> 
> 	value64 = value | value << 8 | value << 16 | value << 24;
> 	value64 = value64 | value64 << 32;
> 
> The integer promotions are performed and sign-extended as the type of value
> is u8.  The upper 32 bits of value64 is 0xffffffff in the first line, and
> the second line has no effect.
> 
> This fixes the 64-bit pattern generation.
> 
> Signed-off-by: Akinobu Mita <akinobu.mita@...il.com>
> Cc: Christoph Lameter <cl@...ux-foundation.org>
> Cc: Pekka Enberg <penberg@...nel.org>
> Cc: Matt Mackall <mpm@...enic.com>
> Cc: linux-mm@...ck.org
> ---
>  mm/slub.c |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
> 
> diff --git a/mm/slub.c b/mm/slub.c
> index eb5a8f9..5695f92 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -701,7 +701,7 @@ static u8 *check_bytes(u8 *start, u8 value, unsigned int bytes)
>  		return check_bytes8(start, value, bytes);
>  
>  	value64 = value | value << 8 | value << 16 | value << 24;
> -	value64 = value64 | value64 << 32;
> +	value64 = (value64 & 0xffffffff) | value64 << 32;
>  	prefix = 8 - ((unsigned long)start) % 8;
>  
>  	if (prefix) {

Still buggy I am afraid. Could we use the following ?


	value64 = value;
	value64 |= value64 << 8;
	value64 |= value64 << 16;
	value64 |= value64 << 32;



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