mm,memory_hotplug: drop unneeded locking

Currently, memory-hotplug code takes zone's span_writelock and pgdat's
resize_lock when resizing the node/zone's spanned pages via
{move_pfn_range_to_zone(),remove_pfn_range_from_zone()} and when resizing
node and zone's present pages via adjust_present_page_count().

These locks are also taken during the initialization of the system at boot
time, where it protects parallel struct page initialization, but they
should not really be needed in memory-hotplug where all operations are a)
synchronized on device level and b) serialized by the mem_hotplug_lock
lock.

[akpm@linux-foundation.org: remove now-unused locals]

Link: https://lkml.kernel.org/r/20210531093958.15021-1-osalvador@suse.de
Signed-off-by: Oscar Salvador <osalvador@suse.de>
Acked-by: David Hildenbrand <david@redhat.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Pavel Tatashin <pasha.tatashin@soleen.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/memory_hotplug.c

@@ -329,7 +329,6 @@ static void shrink_zone_span(struct zone *zone, unsigned long start_pfn,
 	unsigned long pfn;
 	int nid = zone_to_nid(zone);
 
-	zone_span_writelock(zone);
 	if (zone->zone_start_pfn == start_pfn) {
 		/*
 		 * If the section is smallest section in the zone, it need
@@ -362,7 +361,6 @@ static void shrink_zone_span(struct zone *zone, unsigned long start_pfn,
 			zone->spanned_pages = 0;
 		}
 	}
-	zone_span_writeunlock(zone);
 }
 
 static void update_pgdat_span(struct pglist_data *pgdat)
@@ -399,7 +397,7 @@ void __ref remove_pfn_range_from_zone(struct zone *zone,
 {
 	const unsigned long end_pfn = start_pfn + nr_pages;
 	struct pglist_data *pgdat = zone->zone_pgdat;
-	unsigned long pfn, cur_nr_pages, flags;
+	unsigned long pfn, cur_nr_pages;
 
 	/* Poison struct pages because they are now uninitialized again. */
 	for (pfn = start_pfn; pfn < end_pfn; pfn += cur_nr_pages) {
@@ -424,10 +422,8 @@ void __ref remove_pfn_range_from_zone(struct zone *zone,
 
 	clear_zone_contiguous(zone);
 
-	pgdat_resize_lock(zone->zone_pgdat, &flags);
 	shrink_zone_span(zone, start_pfn, start_pfn + nr_pages);
 	update_pgdat_span(pgdat);
-	pgdat_resize_unlock(zone->zone_pgdat, &flags);
 
 	set_zone_contiguous(zone);
 }
@@ -634,19 +630,13 @@ void __ref move_pfn_range_to_zone(struct zone *zone, unsigned long start_pfn,
 {
 	struct pglist_data *pgdat = zone->zone_pgdat;
 	int nid = pgdat->node_id;
-	unsigned long flags;
 
 	clear_zone_contiguous(zone);
 
-	/* TODO Huh pgdat is irqsave while zone is not. It used to be like that before */
-	pgdat_resize_lock(pgdat, &flags);
-	zone_span_writelock(zone);
 	if (zone_is_empty(zone))
 		init_currently_empty_zone(zone, start_pfn, nr_pages);
 	resize_zone_range(zone, start_pfn, nr_pages);
-	zone_span_writeunlock(zone);
 	resize_pgdat_range(pgdat, start_pfn, nr_pages);
-	pgdat_resize_unlock(pgdat, &flags);
 
 	/*
 	 * Subsection population requires care in pfn_to_online_page().
@@ -736,12 +726,8 @@ struct zone *zone_for_pfn_range(int online_type, int nid, unsigned start_pfn,
  */
 void adjust_present_page_count(struct zone *zone, long nr_pages)
 {
-	unsigned long flags;
-
 	zone->present_pages += nr_pages;
-	pgdat_resize_lock(zone->zone_pgdat, &flags);
 	zone->zone_pgdat->node_present_pages += nr_pages;
-	pgdat_resize_unlock(zone->zone_pgdat, &flags);
 }
 
 int mhp_init_memmap_on_memory(unsigned long pfn, unsigned long nr_pages,