Date:   Wed, 8 Dec 2021 09:54:24 +0100
From:   Michal Hocko <mhocko@suse.com>
To:     Alexey Makhalov <amakhalov@vmware.com>
Cc:     Dennis Zhou <dennis@kernel.org>,
        Eric Dumazet <eric.dumazet@gmail.com>,
        "linux-mm@kvack.org" <linux-mm@kvack.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        David Hildenbrand <david@redhat.com>,
        Oscar Salvador <osalvador@suse.de>, Tejun Heo <tj@kernel.org>,
        Christoph Lameter <cl@linux.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "stable@vger.kernel.org" <stable@vger.kernel.org>
Subject: Re: [PATCH v3] mm: fix panic in __alloc_pages
Message-ID: <YbBywDwc2bCxWGAQ@dhcp22.suse.cz>
References: <20211108202325.20304-1-amakhalov@vmware.com>
 <2e191db3-286f-90c6-bf96-3f89891e9926@gmail.com>
 <YYqstfX8PSGDfWsn@dhcp22.suse.cz>
 <YYrGpn/52HaLCAyo@fedora>
 <YYrSC7vtSQXz652a@dhcp22.suse.cz>
 <BAE95F0C-FAA7-40C6-A0D6-5049B1207A27@vmware.com>
 <YZN3ExwL7BiDS5nj@dhcp22.suse.cz>
 <5239D699-523C-4F0C-923A-B068E476043E@vmware.com>
 <YZYQUn10DrKhSE7L@dhcp22.suse.cz>
 <Ya89aqij6nMwJrIZ@dhcp22.suse.cz>
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Alexey,
this is still not finalized but it would really help if you could give
it a spin on your setup. I still have to think about how to transition
from a memoryless node to standard node (in hotplug code). Also there
might be other surprises on the way.

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index c5952749ad40..8ed8db2ccb13 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 +8036,32 @@ 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);
+
+			/* Allocator not initialized yet */
+			pgdat = memblock_alloc(sizeof(*pgdat), SMP_CACHE_BYTES);
+			if (!pgdat) {
+				pr_err("Cannot allocate %zuB for node %d.\n",
+						sizeof(*pgdat), nid);
+				continue;
+			}
+			/* TODO do we need this for memoryless nodes */
+			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