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

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Date:   Tue, 7 Dec 2021 17:40:36 +0100
From:   David Hildenbrand <david@...hat.com>
To:     Michal Hocko <mhocko@...e.com>
Cc:     Alexey Makhalov <amakhalov@...are.com>,
        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>,
        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>
Subject: Re: [PATCH v3] mm: fix panic in __alloc_pages

On 07.12.21 17:36, Michal Hocko wrote:
> 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);

Is the buddy fully up an running at that point? I don't think so, so we
might have to allocate via memblock instead. But I might be wrong.

> +			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 */
> 

Yes, and maybe in the same go, remove/rework hotadd_new_pgdat(), because
there is nothing  to hotadd anymore. (we should double-check the
initialization performed in there, it might all not be necessary anymore)

-- 
Thanks,

David / dhildenb