Patch "cpumask: fix spurious cpumask_of_node() on non-NUMA multi-node configs" has been added to the 4.9-stable tree

[<gregkh@linuxfoundation.org>]

This is a note to let you know that I've just added the patch titled

    cpumask: fix spurious cpumask_of_node() on non-NUMA multi-node configs

to the 4.9-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     cpumask-fix-spurious-cpumask_of_node-on-non-numa-multi-node-configs.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From b339752d054fb32863418452dff350a1086885b1 Mon Sep 17 00:00:00 2001
From: Tejun Heo <tj@kernel.org>
Date: Mon, 28 Aug 2017 14:51:27 -0700
Subject: cpumask: fix spurious cpumask_of_node() on non-NUMA multi-node configs

From: Tejun Heo <tj@kernel.org>

commit b339752d054fb32863418452dff350a1086885b1 upstream.

When !NUMA, cpumask_of_node(@node) equals cpu_online_mask regardless of
@node.  The assumption seems that if !NUMA, there shouldn't be more than
one node and thus reporting cpu_online_mask regardless of @node is
correct.  However, that assumption was broken years ago to support
DISCONTIGMEM and whether a system has multiple nodes or not is
separately controlled by NEED_MULTIPLE_NODES.

This means that, on a system with !NUMA && NEED_MULTIPLE_NODES,
cpumask_of_node() will report cpu_online_mask for all possible nodes,
indicating that the CPUs are associated with multiple nodes which is an
impossible configuration.

This bug has been around forever but doesn't look like it has caused any
noticeable symptoms.  However, it triggers a WARN recently added to
workqueue to verify NUMA affinity configuration.

Fix it by reporting empty cpumask on non-zero nodes if !NUMA.

Signed-off-by: Tejun Heo <tj@kernel.org>
Reported-and-tested-by: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 include/asm-generic/topology.h |    6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

--- a/include/asm-generic/topology.h
+++ b/include/asm-generic/topology.h
@@ -48,7 +48,11 @@
 #define parent_node(node)	((void)(node),0)
 #endif
 #ifndef cpumask_of_node
-#define cpumask_of_node(node)	((void)node, cpu_online_mask)
+  #ifdef CONFIG_NEED_MULTIPLE_NODES
+    #define cpumask_of_node(node)	((node) == 0 ? cpu_online_mask : cpu_none_mask)
+  #else
+    #define cpumask_of_node(node)	((void)node, cpu_online_mask)
+  #endif
 #endif
 #ifndef pcibus_to_node
 #define pcibus_to_node(bus)	((void)(bus), -1)


Patches currently in stable-queue which might be from tj@kernel.org are

queue-4.9/cpumask-fix-spurious-cpumask_of_node-on-non-numa-multi-node-configs.patch
queue-4.9/cpuset-fix-incorrect-memory_pressure-control-file-mapping.patch