From: Marcin Slusarz <marcin.slusarz@gmail.com>
To: Akinobu Mita <akinobu.mita@gmail.com>
Cc: linux-kernel@vger.kernel.org,
Christoph Lameter <cl@linux-foundation.org>,
Pekka Enberg <penberg@kernel.org>, Matt Mackall <mpm@selenic.com>,
linux-mm@kvack.org
Subject: Re: [PATCH] slub: fix check_bytes() for slub debugging
Date: Mon, 8 Aug 2011 23:24:18 +0200 [thread overview]
Message-ID: <20110808212418.GA3297@joi.lan> (raw)
In-Reply-To: <1312709438-7608-1-git-send-email-akinobu.mita@gmail.com>
On Sun, Aug 07, 2011 at 06:30:38PM +0900, Akinobu Mita wrote:
> 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.
Thank you. I'm a bit ashamed about this bug... I introduced this bug, so:
Reviewed-by: Marcin Slusarz <marcin.slusarz@gmail.com>
I tested your patch to check if performance improvements of commit
c4089f98e943ff445665dea49c190657b34ccffe come from this bug or not.
And forunately they aren't - performance is exactly the same.
How did you find it?
Marcin
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next prev parent reply other threads:[~2011-08-08 21:24 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-08-07 9:30 [PATCH] slub: fix check_bytes() for slub debugging Akinobu Mita
2011-08-08 21:24 ` Marcin Slusarz [this message]
2011-08-09 1:08 ` Akinobu Mita
2011-08-09 3:10 ` Eric Dumazet
2011-08-09 3:33 ` Eric Dumazet
2011-08-09 9:38 ` Akinobu Mita
2011-08-09 9:43 ` Pekka Enberg
2011-08-09 9:54 ` Eric Dumazet
2011-08-09 9:46 ` Eric Dumazet
2011-08-09 21:46 ` Marcin Slusarz
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