mm: do not iterate over NR_CPUS in __zone_pcp_update()

__zone_pcp_update() iterates over NR_CPUS instead of limiting the access
to the possible cpus.  This might result in access to uninitialized areas
as the per cpu allocator only populates the per cpu memory for possible
cpus.

This problem was created as a result of the dynamic allocation of pagesets
from percpu memory that went in during the merge window - commit
99dcc3e5a94ed491fbef402831d8c0bbb267f995 ("this_cpu: Page allocator
conversion").

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Pekka Enberg <penberg@cs.helsinki.fi>
Acked-by: Tejun Heo <tj@kernel.org>
Acked-by: Christoph Lameter <cl@linux-foundation.org>
Acked-by: Mel Gorman <mel@csn.ul.ie>
Reviewed-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index a8182c89de5920b5eb91809676ee884d89bbfcaf..78ce90dd671f186e02323e45d3c10022bbecf5ec 100644 (file)
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -3224,7 +3224,7 @@ static int __zone_pcp_update(void *data)
        int cpu;
        unsigned long batch = zone_batchsize(zone), flags;
 
-       for (cpu = 0; cpu < NR_CPUS; cpu++) {
+       for_each_possible_cpu(cpu) {
                struct per_cpu_pageset *pset;
                struct per_cpu_pages *pcp;