Re: [PATCH v3] mm: fix panic in __alloc_pages

[Michal Hocko]

On Tue 07-12-21 17:27:29, Michal Hocko wrote:
[...]
> So your proposal is to drop set_node_online from the patch and add it as
> a separate one which handles 
> 	- sysfs part (i.e. do not register a node which doesn't span a
> 	  physical address space)
> 	- hotplug side of (drop the pgd allocation, register node lazily
> 	  when a first memblocks are registered)

In other words, the first stage
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index c5952749ad40..f9024ba09c53 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -6382,7 +6382,11 @@ static void __build_all_zonelists(void *data)
 	if (self && !node_online(self->node_id)) {
 		build_zonelists(self);
 	} else {
-		for_each_online_node(nid) {
+		/*
+		 * All possible nodes have pgdat preallocated
+		 * free_area_init
+		 */
+		for_each_node(nid) {
 			pg_data_t *pgdat = NODE_DATA(nid);
 
 			build_zonelists(pgdat);
@@ -8032,8 +8036,24 @@ void __init free_area_init(unsigned long *max_zone_pfn)
 	/* Initialise every node */
 	mminit_verify_pageflags_layout();
 	setup_nr_node_ids();
-	for_each_online_node(nid) {
-		pg_data_t *pgdat = NODE_DATA(nid);
+	for_each_node(nid) {
+		pg_data_t *pgdat;
+
+		if (!node_online(nid)) {
+			pr_warn("Node %d uninitialized by the platform. Please report with boot dmesg.\n", nid);
+			pgdat = arch_alloc_nodedata(nid);
+			pgdat->per_cpu_nodestats = alloc_percpu(struct per_cpu_nodestat);
+			arch_refresh_nodedata(nid, pgdat);
+			free_area_init_memoryless_node(nid);
+			/*
+			 * not marking this node online because we do not want to
+			 * confuse userspace by sysfs files/directories for node
+			 * without any memory attached to it (see topology_init)
+			 */
+			continue;
+		}
+
+		pgdat = NODE_DATA(nid);
 		free_area_init_node(nid);
 
 		/* Any memory on that node */
-- 
Michal Hocko
SUSE Labs