From f2e12bb272f2544d1504f982270e90ae3dcc4ff2 Mon Sep 17 00:00:00 2001 From: Christoph Lameter Date: Fri, 5 Jan 2007 16:37:02 -0800 Subject: [PATCH] [PATCH] Check for populated zone in __drain_pages Both process_zones() and drain_node_pages() check for populated zones before touching pagesets. However, __drain_pages does not do so, This may result in a NULL pointer dereference for pagesets in unpopulated zones if a NUMA setup is combined with cpu hotplug. Initially the unpopulated zone has the pcp pointers pointing to the boot pagesets. Since the zone is not populated the boot pageset pointers will not be changed during page allocator and slab bootstrap. If a cpu is later brought down (first call to __drain_pages()) then the pcp pointers for cpus in unpopulated zones are set to NULL since __drain_pages does not first check for an unpopulated zone. If the cpu is then brought up again then we call process_zones() which will ignore the unpopulated zone. So the pageset pointers will still be NULL. If the cpu is then again brought down then __drain_pages will attempt to drain pages by following the NULL pageset pointer for unpopulated zones. Signed-off-by: Christoph Lameter Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/page_alloc.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/mm/page_alloc.c b/mm/page_alloc.c index 4a9a83fc1b39..a49f96b7ea43 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -711,6 +711,9 @@ static void __drain_pages(unsigned int cpu) for_each_zone(zone) { struct per_cpu_pageset *pset; + if (!populated_zone(zone)) + continue; + pset = zone_pcp(zone, cpu); for (i = 0; i < ARRAY_SIZE(pset->pcp); i++) { struct per_cpu_pages *pcp; -- 2.20.1