Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933026AbYGRAFw (ORCPT ); Thu, 17 Jul 2008 20:05:52 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1759570AbYGRAFk (ORCPT ); Thu, 17 Jul 2008 20:05:40 -0400 Received: from wf-out-1314.google.com ([209.85.200.169]:8089 "EHLO wf-out-1314.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1759064AbYGRAFk (ORCPT ); Thu, 17 Jul 2008 20:05:40 -0400 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=message-id:date:from:to:subject:cc:in-reply-to:mime-version :content-type:content-transfer-encoding:content-disposition :references; b=dv14Rh4UDa+NoUfdbcELP77F3NqZJlawmcw9M6twqbv9TKmuzjtk62WwnXNwFYJyNp WNLZmKeLE93040/5AC+YdRshLS0177+P0bdVRX2dux2DdCHdJrkxKIeAsbPQnaFKYHgl zPx3QzODIlxetF4XzqWeDXOPgLp1K/kQjqWpM= Message-ID: <19f34abd0807171705h31595809y944792ce697bede7@mail.gmail.com> Date: Fri, 18 Jul 2008 02:05:39 +0200 From: "Vegard Nossum" To: "Ingo Molnar" Subject: Re: [bug, netconsole, SLUB] BUG skbuff_head_cache: Poison overwritten Cc: linux-kernel@vger.kernel.org, netdev@vger.kernel.org, "Pekka Enberg" , "Rafael J. Wysocki" In-Reply-To: <20080717235254.GA6833@elte.hu> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Content-Disposition: inline References: <20080717214222.GA29449@elte.hu> <19f34abd0807171615s5b477d4cr22d3e9444bcf65df@mail.gmail.com> <20080717235254.GA6833@elte.hu> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2102 Lines: 61 On Fri, Jul 18, 2008 at 1:52 AM, Ingo Molnar wrote: > If only we had some kernel technology that could track and validate > memory accesses, and point out the cases where we access uninitialized > memory, just like Valgrind? > > ... something like kmemcheck? ;-) Cool :) > So i booted that box with tip/master and kmemcheck enabled. (plus a few > fixlets to make networking allocations be properly tracked by > kmemcheck.) > > It was a slow bootup and long wait, but it gave a few hits here: Hm, if you think it was that slow, I am suspecting you were also using SLUB debugging. This can actually be negative, since now SLUB will access the objects (+redzone +padding) and possibly trick kmemcheck into thinking they were initialized in the first place. But what we are really looking for is "read from freed memory" messages. So I would actually recommend this: Disable kmemcheck's reporting of uninitialized memory, simply to make it easier to spot the "freed" messages more easily. Maybe something like this (warning: whitespace-munged): diff --git a/arch/x86/mm/kmemcheck/error.c b/arch/x86/mm/kmemcheck/error.c index 56410c6..6944cb7 100644 --- a/arch/x86/mm/kmemcheck/error.c +++ b/arch/x86/mm/kmemcheck/error.c @@ -98,6 +98,9 @@ void kmemcheck_error_save(enum kmemcheck_shadow state, return; prev_ip = regs->ip; + if (state == KMEMCHECK_SHADOW_UNINITIALIZED) + return; + e = error_next_wr(); if (!e) return; If this only happens during boot, it would also be a good idea to simply reboot the machine a lot... Vegard -- "The animistic metaphor of the bug that maliciously sneaked in while the programmer was not looking is intellectually dishonest as it disguises that the error is the programmer's own creation." -- E. W. Dijkstra, EWD1036 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/