Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758958AbZFPO5W (ORCPT ); Tue, 16 Jun 2009 10:57:22 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753133AbZFPO5G (ORCPT ); Tue, 16 Jun 2009 10:57:06 -0400 Received: from relay1.sgi.com ([192.48.179.29]:57860 "EHLO relay.sgi.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1752551AbZFPO5F (ORCPT ); Tue, 16 Jun 2009 10:57:05 -0400 Date: Tue, 16 Jun 2009 09:57:06 -0500 From: Dimitri Sivanich To: linux-kernel@vger.kernel.org Subject: [PATCH] page_alloc: Oops when setting percpu_pagelist_fraction Message-ID: <20090616145706.GB14680@sgi.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.5.17 (2007-11-01) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2222 Lines: 57 After downing/upping a cpu, an attempt to set /proc/sys/vm/percpu_pagelist_fraction results in an oops in percpu_pagelist_fraction_sysctl_handler(). To reproduce this: localhost:/sys/devices/system/cpu/cpu6 # echo 0 >online localhost:/sys/devices/system/cpu/cpu6 # echo 1 >online localhost:/sys/devices/system/cpu/cpu6 # cd /proc/sys/vm localhost:/proc/sys/vm # echo 100000 >percpu_pagelist_fraction BUG: unable to handle kernel NULL pointer dereference at 0000000000000004 IP: [] percpu_pagelist_fraction_sysctl_handler+0x4a/0x96 This is because the zone->pageset[cpu] value has not been set when the cpu has been brought back up for unpopulated zones (the "Movable" zone in the case I'm running into). Prior to downing/upping the cpu it had been set to &boot_pageset[cpu]. There are two possible fixes that come to mind. One is to check for an unpopulated zone or NULL zone pageset for that cpu in percpu_pagelist_fraction_sysctl_handler(), and simply not set a pagelist highmark for that zone/cpu combination. The other, and the one I'm proposing here, is to set the zone's pageset back to the boot_pageset when the cpu is brought back up if the zone is unpopulated. Signed-off-by: Dimitri Sivanich --- mm/page_alloc.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) Index: linux/mm/page_alloc.c =================================================================== --- linux.orig/mm/page_alloc.c 2009-06-16 09:25:25.000000000 -0500 +++ linux/mm/page_alloc.c 2009-06-16 09:27:47.000000000 -0500 @@ -2806,7 +2806,11 @@ static int __cpuinit process_zones(int c node_set_state(node, N_CPU); /* this node has a cpu */ - for_each_populated_zone(zone) { + for_each_zone(zone) { + if (!populated_zone(zone)) { + zone_pcp(zone, cpu) = &boot_pageset[cpu]; + continue; + } zone_pcp(zone, cpu) = kmalloc_node(sizeof(struct per_cpu_pageset), GFP_KERNEL, node); if (!zone_pcp(zone, cpu)) -- 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/