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Subject[PATCH 1/3] powerpc: Allocate per-cpu areas for node IDs for SLQB to use as per-node areas
SLQB uses DEFINE_PER_CPU to define per-node areas. An implicit
assumption is made that all valid node IDs will have matching valid CPU
ids. In memoryless configurations, it is possible to have a node ID with
no CPU having the same ID. When this happens, a per-cpu are is not
created and the value of paca[cpu].data_offset is some random value.
This is later deferenced and the system crashes after accessing some
invalid address.

This patch hacks powerpc to allocate per-cpu areas for node IDs that
have no corresponding CPU id. This gets around the immediate problem but
it should be discussed if there is a requirement for a DEFINE_PER_NODE
and how it should be implemented.

Signed-off-by: Mel Gorman <>
arch/powerpc/kernel/setup_64.c | 20 ++++++++++++++++++++
1 files changed, 20 insertions(+), 0 deletions(-)

diff --git a/arch/powerpc/kernel/setup_64.c b/arch/powerpc/kernel/setup_64.c
index 1f68160..a5f52d4 100644
--- a/arch/powerpc/kernel/setup_64.c
+++ b/arch/powerpc/kernel/setup_64.c
@@ -588,6 +588,26 @@ void __init setup_per_cpu_areas(void)
paca[i].data_offset = ptr - __per_cpu_start;
memcpy(ptr, __per_cpu_start, __per_cpu_end - __per_cpu_start);
+ /*
+ * SLQB abuses DEFINE_PER_CPU to setup a per-node area. This trick
+ * assumes that ever node ID will have a CPU of that ID to match.
+ * On systems with memoryless nodes, this may not hold true. Hence,
+ * we take a second pass initialising a "per-cpu" area for node-ids
+ * that SLQB can use
+ */
+ for_each_node_state(i, N_NORMAL_MEMORY) {
+ /* Skip node IDs that a valid CPU id exists for */
+ if (paca[i].data_offset)
+ continue;
+ ptr = alloc_bootmem_pages_node(NODE_DATA(cpu_to_node(i)), size);
+ paca[i].data_offset = ptr - __per_cpu_start;
+ memcpy(ptr, __per_cpu_start, __per_cpu_end - __per_cpu_start);
+ }
+#endif /* CONFIG_SLQB */


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