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

On Mon 13-12-21 16:07:18, David Hildenbrand wrote:

On 13.12.21 16:06, Michal Hocko wrote:

quoted

On Thu 09-12-21 11:48:42, Michal Hocko wrote:
[...]

quoted

diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index 852041f6be41..2d38a431f62f 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c

@@ -1161,19 +1161,21 @@ static void reset_node_present_pages(pg_data_t *pgdat)
 }
 
 /* we are OK calling __meminit stuff here - we have CONFIG_MEMORY_HOTPLUG */
-static pg_data_t __ref *hotadd_new_pgdat(int nid)
+static pg_data_t __ref *hotadd_init_pgdat(int nid)
 {
 	struct pglist_data *pgdat;
 
 	pgdat = NODE_DATA(nid);
-	if (!pgdat) {
-		pgdat = arch_alloc_nodedata(nid);
-		if (!pgdat)
-			return NULL;
 
+	/*
+	 * NODE_DATA is preallocated (free_area_init) but its internal
+	 * state is not allocated completely. Add missing pieces.
+	 * Completely offline nodes stay around and they just need
+	 * reintialization.
+	 */
+	if (!pgdat->per_cpu_nodestats) {
 		pgdat->per_cpu_nodestats =
 			alloc_percpu(struct per_cpu_nodestat);
-		arch_refresh_nodedata(nid, pgdat);

This should really be 

diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index 42211485bcf3..2daa88ce8c80 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c

@@ -1173,7 +1173,7 @@ static pg_data_t __ref *hotadd_init_pgdat(int nid)
 	 * Completely offline nodes stay around and they just need
 	 * reintialization.
 	 */
-	if (!pgdat->per_cpu_nodestats) {
+	if (pgdat->per_cpu_nodestats == &boot_nodestats) {
 		pgdat->per_cpu_nodestats =
 			alloc_percpu(struct per_cpu_nodestat);
 	} else {

I'll try giving this some churn later this week -- busy with other stuff.

Please hang on, this needs to be done yet slightly differently. I will
post something more resembling a final patch later today. For the
purpose of the testing this should be sufficient for now.
-- 
Michal Hocko
SUSE Labs