mm: page_alloc: avoid false page outside zone error info

If pfn is outside zone boundaries in the first round, ret will be set to
1.  But if pfn is changed to inside the zone boundaries in zone span
seqretry path, ret is still set to 1 leading to false page outside zone
error info.

This is from code inspection.  The race window should be really small thus
hard to trigger in real world.

[akpm@linux-foundation.org: code simplification, per Matthew]
Link: https://lkml.kernel.org/r/20230704111823.940331-1-linmiaohe@huawei.com
Fixes: bdc8cb9 ("[PATCH] memory hotplug locking: zone span seqlock")
Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
Cc: Matthew Wilcox <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/page_alloc.c

@@ -459,7 +459,7 @@ void set_pageblock_migratetype(struct page *page, int migratetype)
 #ifdef CONFIG_DEBUG_VM
 static int page_outside_zone_boundaries(struct zone *zone, struct page *page)
 {
-	int ret = 0;
+	int ret;
 	unsigned seq;
 	unsigned long pfn = page_to_pfn(page);
 	unsigned long sp, start_pfn;
@@ -468,8 +468,7 @@ static int page_outside_zone_boundaries(struct zone *zone, struct page *page)
 		seq = zone_span_seqbegin(zone);
 		start_pfn = zone->zone_start_pfn;
 		sp = zone->spanned_pages;
-		if (!zone_spans_pfn(zone, pfn))
-			ret = 1;
+		ret = !zone_spans_pfn(zone, pfn);
 	} while (zone_span_seqretry(zone, seq));
 
 	if (ret)