From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail138.messagelabs.com (mail138.messagelabs.com [216.82.249.35]) by kanga.kvack.org (Postfix) with ESMTP id D858E6B0169 for ; Mon, 8 Aug 2011 23:33:10 -0400 (EDT) Received: by wwj26 with SMTP id 26so2911191wwj.2 for ; Mon, 08 Aug 2011 20:33:08 -0700 (PDT) Subject: Re: [PATCH] slub: fix check_bytes() for slub debugging From: Eric Dumazet In-Reply-To: <1312859440.2531.20.camel@edumazet-laptop> References: <1312709438-7608-1-git-send-email-akinobu.mita@gmail.com> <1312859440.2531.20.camel@edumazet-laptop> Content-Type: text/plain; charset="UTF-8" Date: Tue, 09 Aug 2011 05:33:03 +0200 Message-ID: <1312860783.2531.31.camel@edumazet-laptop> Mime-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: owner-linux-mm@kvack.org List-ID: To: Akinobu Mita Cc: linux-kernel@vger.kernel.org, Christoph Lameter , Pekka Enberg , Matt Mackall , linux-mm@kvack.org Le mardi 09 aoA>>t 2011 A 05:10 +0200, Eric Dumazet a A(C)crit : > Le dimanche 07 aoA>>t 2011 A 18:30 +0900, Akinobu Mita a A(C)crit : > > 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 > > Cc: Christoph Lameter > > Cc: Pekka Enberg > > Cc: Matt Mackall > > Cc: linux-mm@kvack.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; > > 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 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: email@kvack.org