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

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Message-ID: <CAOJsxLHKJT_qCsiPVCEh=+nbZ2D7+y=mJgMM+wEob395zEN6XQ@mail.gmail.com>
Date:	Tue, 9 Aug 2011 12:43:26 +0300
From:	Pekka Enberg <penberg@...nel.org>
To:	Akinobu Mita <akinobu.mita@...il.com>
Cc:	Eric Dumazet <eric.dumazet@...il.com>,
	linux-kernel@...r.kernel.org,
	Christoph Lameter <cl@...ux-foundation.org>,
	Matt Mackall <mpm@...enic.com>, linux-mm@...ck.org
Subject: Re: [PATCH] slub: fix check_bytes() for slub debugging

On Tue, Aug 9, 2011 at 12:38 PM, Akinobu Mita <akinobu.mita@...il.com> wrote:
> 2011/8/9 Eric Dumazet <eric.dumazet@...il.com>:
>
>>> > 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;
>>>
>>>
>>
>> Well, 'buggy' was not well chosen.
>>
>> Another possibility would be to use a multiply if arch has a fast
>> multiplier...
>>
>>
>>        value64 = value;
>> #if defined(ARCH_HAS_FAST_MULTIPLIER) && BITS_PER_LONG == 64
>>        value64 *= 0x0101010101010101;
>> #elif defined(ARCH_HAS_FAST_MULTIPLIER)
>>        value64 *= 0x01010101;
>>        value64 |= value64 << 32;
>> #else
>>        value64 |= value64 << 8;
>>        value64 |= value64 << 16;
>>        value64 |= value64 << 32;
>> #endif
>
> I don't really care about which one should be used.  So tell me if I need
> to resend it with this improvement.

I'm confused. What was wrong with your original patch?

                        Pekka
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