linux-kernel - [PATCH v2 1/4] mm,hwpoison,hugetlb,memory_hotplug: hotremove memory section with hwpoisoned hugepage

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Date:   Mon,  5 Sep 2022 15:21:34 +0900
From:   Naoya Horiguchi <naoya.horiguchi@...ux.dev>
To:     linux-mm@...ck.org
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Miaohe Lin <linmiaohe@...wei.com>,
        David Hildenbrand <david@...hat.com>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Yang Shi <shy828301@...il.com>,
        Oscar Salvador <osalvador@...e.de>,
        Muchun Song <songmuchun@...edance.com>,
        Jane Chu <jane.chu@...cle.com>,
        Naoya Horiguchi <naoya.horiguchi@....com>,
        linux-kernel@...r.kernel.org
Subject: [PATCH v2 1/4] mm,hwpoison,hugetlb,memory_hotplug: hotremove memory section with hwpoisoned hugepage

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

HWPoisoned page is not supposed to be accessed once marked, but currently
such accesses can happen during memory hotremove because do_migrate_range()
can be called before dissolve_free_huge_pages() is called.

Move dissolve_free_huge_pages() before scan_movable_pages(). Recently
delayed dissolve has been implemented, so the dissolving can turn
a hwpoisoned hugepage into 4kB hwpoison page, which memory hotplug can
handle safely.

Reported-by: Miaohe Lin <linmiaohe@...wei.com>
Signed-off-by: Naoya Horiguchi <naoya.horiguchi@....com>
---
 mm/memory_hotplug.c | 22 +++++++++++-----------
 1 file changed, 11 insertions(+), 11 deletions(-)

diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index fad6d1f2262a..c24735d63b25 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -1880,6 +1880,17 @@ int __ref offline_pages(unsigned long start_pfn, unsigned long nr_pages,
 
 			cond_resched();
 
+			/*
+			 * Dissolve free hugepages in the memory block before doing
+			 * offlining actually in order to make hugetlbfs's object
+			 * counting consistent.
+			 */
+			ret = dissolve_free_huge_pages(start_pfn, end_pfn);
+			if (ret) {
+				reason = "failure to dissolve huge pages";
+				goto failed_removal_isolated;
+			}
+
 			ret = scan_movable_pages(pfn, end_pfn, &pfn);
 			if (!ret) {
 				/*
@@ -1895,17 +1906,6 @@ int __ref offline_pages(unsigned long start_pfn, unsigned long nr_pages,
 			goto failed_removal_isolated;
 		}
 
-		/*
-		 * Dissolve free hugepages in the memory block before doing
-		 * offlining actually in order to make hugetlbfs's object
-		 * counting consistent.
-		 */
-		ret = dissolve_free_huge_pages(start_pfn, end_pfn);
-		if (ret) {
-			reason = "failure to dissolve huge pages";
-			goto failed_removal_isolated;
-		}
-
 		ret = test_pages_isolated(start_pfn, end_pfn, MEMORY_OFFLINE);
 
 	} while (ret);
-- 
2.25.1