Commit:     f2e12bb272f2544d1504f982270e90ae3dcc4ff2
Parent:     6929da4427b4335365dd51ab0b7dd2a0393656f0
Author:     Christoph Lameter <[EMAIL PROTECTED]>
AuthorDate: Fri Jan 5 16:37:02 2007 -0800
Committer:  Linus Torvalds <[EMAIL PROTECTED]>
CommitDate: Fri Jan 5 23:55:29 2007 -0800

    [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 <[EMAIL PROTECTED]>
    Signed-off-by: Andrew Morton <[EMAIL PROTECTED]>
    Signed-off-by: Linus Torvalds <[EMAIL PROTECTED]>
 mm/page_alloc.c |    3 +++
 1 files changed, 3 insertions(+), 0 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 4a9a83f..a49f96b 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;
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