[PATCHv2 3/3] powerpc/numa: make all possible node be instanced against NULL reference in node_zonelist()

From: Pingfan Liu
Date: Thu Dec 20 2018 - 04:51:28 EST

This patch tries to resolve a bug rooted at mm when using nr_cpus. It was
reported at [1]. The root cause is: device->numa_node info is used as
preferred_nid param for __alloc_pages_nodemask(), which causes NULL
reference when ac->zonelist = node_zonelist(preferred_nid, gfp_mask), due to
the preferred_nid is not online and not instanced. Hence the bug affects
all archs if a machine having a memory less numa-node, but a device on the
node is used and provide numa_node info to __alloc_pages_nodemask().
This patch makes all possible node online for ppc.

[1]: https://lore.kernel.org/patchwork/patch/1020838/

Signed-off-by: Pingfan Liu <kernelfans@xxxxxxxxx>
Cc: linuxppc-dev@xxxxxxxxxxxxxxxx
Cc: x86@xxxxxxxxxx
Cc: linux-kernel@xxxxxxxxxxxxxxx
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxx>
Cc: Mike Rapoport <rppt@xxxxxxxxxxxxxxxxxx>
Cc: Bjorn Helgaas <bhelgaas@xxxxxxxxxx>
Cc: Jonathan Cameron <Jonathan.Cameron@xxxxxxxxxx>
Cc: David Rientjes <rientjes@xxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
Cc: Benjamin Herrenschmidt <benh@xxxxxxxxxxxxxxxxxxx>
Cc: Paul Mackerras <paulus@xxxxxxxxx>
Cc: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
[1-2/3] implements one way to fix the bug, while this patch tries another way.
Hence using this patch when [1-2/3] is not acceptable.

arch/powerpc/mm/numa.c | 13 +++++++++++--
1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/arch/powerpc/mm/numa.c b/arch/powerpc/mm/numa.c
index ce28ae5..31d81a4 100644
--- a/arch/powerpc/mm/numa.c
+++ b/arch/powerpc/mm/numa.c
@@ -864,10 +864,19 @@ void __init initmem_init(void)


- for_each_online_node(nid) {
+ /* Instance all possible nodes to overcome potential NULL reference
+ * issue on node_zonelist() when using nr_cpus
+ */
+ for_each_node(nid) {
unsigned long start_pfn, end_pfn;

- get_pfn_range_for_nid(nid, &start_pfn, &end_pfn);
+ if (node_online(nid))
+ get_pfn_range_for_nid(nid, &start_pfn, &end_pfn);
+ else {
+ start_pfn = end_pfn = 0;
+ /* online it, so later zonelists[] will be built */
+ node_set_online(nid);
+ }
setup_node_data(nid, start_pfn, end_pfn);