mm, oom: ensure memoryless node zonelist always includes zones

With memoryless node support being worked on, it's possible that for
optimizations that a node may not have a non-NULL zonelist.  When
CONFIG_NUMA is enabled and node 0 is memoryless, this means the zonelist
for first_online_node may become NULL.

The oom killer requires a zonelist that includes all memory zones for
the sysrq trigger and pagefault out of memory handler.

Ensure that a non-NULL zonelist is always passed to the oom killer.

[akpm@linux-foundation.org: fix non-numa build]
Signed-off-by: David Rientjes <rientjes@google.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Rik van Riel <riel@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/tty/sysrq.c

@@ -355,7 +355,7 @@ static struct sysrq_key_op sysrq_term_op = {
 
 static void moom_callback(struct work_struct *ignored)
 {
-	out_of_memory(node_zonelist(first_online_node, GFP_KERNEL), GFP_KERNEL,
+	out_of_memory(node_zonelist(first_memory_node, GFP_KERNEL), GFP_KERNEL,
 		      0, NULL, true);
 }
 

include/linux/nodemask.h

@@ -430,7 +430,15 @@ static inline int num_node_state(enum node_states state)
 	for_each_node_mask((__node), node_states[__state])
 
 #define first_online_node	first_node(node_states[N_ONLINE])
-#define next_online_node(nid)	next_node((nid), node_states[N_ONLINE])
+#define first_memory_node	first_node(node_states[N_MEMORY])
+static inline int next_online_node(int nid)
+{
+	return next_node(nid, node_states[N_ONLINE]);
+}
+static inline int next_memory_node(int nid)
+{
+	return next_node(nid, node_states[N_MEMORY]);
+}
 
 extern int nr_node_ids;
 extern int nr_online_nodes;
@@ -471,6 +479,7 @@ static inline int num_node_state(enum node_states state)
 	for ( (node) = 0; (node) == 0; (node) = 1)
 
 #define first_online_node	0
+#define first_memory_node	0
 #define next_online_node(nid)	(MAX_NUMNODES)
 #define nr_node_ids		1
 #define nr_online_nodes		1

mm/oom_kill.c

@@ -694,7 +694,7 @@ void pagefault_out_of_memory(void)
 	if (mem_cgroup_oom_synchronize(true))
 		return;
 
-	zonelist = node_zonelist(first_online_node, GFP_KERNEL);
+	zonelist = node_zonelist(first_memory_node, GFP_KERNEL);
 	if (try_set_zonelist_oom(zonelist, GFP_KERNEL)) {
 		out_of_memory(NULL, 0, 0, NULL, false);
 		clear_zonelist_oom(zonelist, GFP_KERNEL);