From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from wolverine01.qualcomm.com ([199.106.114.254]:61848 "EHLO wolverine01.qualcomm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932275Ab0DGAd3 (ORCPT ); Tue, 6 Apr 2010 20:33:29 -0400 Message-ID: <4BBBD2CD.2010205@codeaurora.org> Date: Tue, 06 Apr 2010 17:33:17 -0700 From: Michael Bohan MIME-Version: 1.0 Subject: Re: [PATCH] arm: mm: Don't free prohibited memmap entries References: <> <1270506861-14461-1-git-send-email-mbohan@codeaurora.org> <20100406220817.GE12831@n2100.arm.linux.org.uk> In-Reply-To: <20100406220817.GE12831@n2100.arm.linux.org.uk> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-arm-msm-owner@vger.kernel.org List-ID: To: Russell King - ARM Linux Cc: mel@csn.ul.ie, linux-arm-msm@vger.kernel.org, linux-arm-kernel@lists.infradead.org, Michael Bohan On 4/6/2010 3:08 PM, Russell King - ARM Linux wrote: > 1. are you enabling ARCH_HAS_HOLES_MEMORYMODEL ? > Yes, although this does not impact the problem I'm dealing with. That option is only used for /proc/pagetypeinfo currently. It would be good if we could consolidate ARCH_HAS_HOLES_MEMORYMODEL and HOLES_IN_ZONE, but that may be out of scope for this change. > 2. where does it try to access these page structs without trying > pfn_valid() to check whether a page struct exists first? > The specific piece of code that is causing crashes in my scenario is in vm/page_alloc.c:move_freepages(), called from move_freepages_block(). The code in move_freepages_block aligns the end_pfn to the closest page block, which may take us to invalid memmap entries. The macro that conditionally saves us in this case is the pfn_valid_within(), called from move_freepages(). If HOLES_IN_ZONE is configured, this option calls down to pfn_valid() to make sure the page has a valid memmap entry. There are likely other cases where this is an issue as well that I haven't run into. Michael