linux-kernel - Re: [PATCH v3] mm: fix panic in __alloc

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Date:   Mon, 13 Dec 2021 16:06:31 +0100
From:   Michal Hocko <mhocko@...e.com>
To:     Alexey Makhalov <amakhalov@...are.com>
Cc:     Dennis Zhou <dennis@...nel.org>,
        Eric Dumazet <eric.dumazet@...il.com>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        David Hildenbrand <david@...hat.com>,
        Oscar Salvador <osalvador@...e.de>, Tejun Heo <tj@...nel.org>,
        Christoph Lameter <cl@...ux.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>,
        Nico Pache <npache@...hat.com>
Subject: Re: [PATCH v3] mm: fix panic in __alloc_pages

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