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

Michal Hocko
2021-12-13T15:06:37Z

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