Messages in this thread Patch in this message | | | Date | Tue, 16 Jun 2009 09:57:06 -0500 | From | Dimitri Sivanich <> | Subject | [PATCH] page_alloc: Oops when setting percpu_pagelist_fraction |
| |
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: [<ffffffff80286946>] 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 <sivanich@sgi.com>
---
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))
| |