[RFC PATCH v1 4/4] mm, memory_hotplug: fix inconsistent num_poisoned_pages on memory hotremove

[Naoya Horiguchi <naoya.horiguchi@linux.dev>]

From: Naoya Horiguchi <naoya.horiguchi@nec.com>

When offlining memory section with hwpoisoned pages, the hwpoisons are
canceled. But num_poisoned_pages is not updated for that event, so the
counter becomes inconsistent.

Add num_poisoned_pages_dec() in __offline_isolated_pages(). PageHWPoison
can be set on a tail page of some high order buddy page, so we need check
PageHWPoison on each subpage.

Signed-off-by: Naoya Horiguchi <naoya.horiguchi@nec.com>
---
 mm/page_alloc.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 6e5b4488a0c5..dcd962855617 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -9487,12 +9487,15 @@ void __offline_isolated_pages(unsigned long start_pfn, unsigned long end_pfn)
 	zone = page_zone(pfn_to_page(pfn));
 	spin_lock_irqsave(&zone->lock, flags);
 	while (pfn < end_pfn) {
+		int i;
+
 		page = pfn_to_page(pfn);
 		/*
 		 * The HWPoisoned page may be not in buddy system, and
 		 * page_count() is not 0.
 		 */
 		if (unlikely(!PageBuddy(page) && PageHWPoison(page))) {
+			num_poisoned_pages_dec();
 			pfn++;
 			continue;
 		}
@@ -9510,6 +9513,9 @@ void __offline_isolated_pages(unsigned long start_pfn, unsigned long end_pfn)
 		BUG_ON(page_count(page));
 		BUG_ON(!PageBuddy(page));
 		order = buddy_order(page);
+		for (i = 0; i < 1 << order; i++)
+			if (PageHWPoison(page + i))
+				num_poisoned_pages_dec();
 		del_page_from_free_list(page, zone, order);
 		pfn += (1 << order);
 	}
-- 
2.25.1