[PATCH V3 1/2] MCE: fix an error of mce_bad_pages statistics

[Xishi Qiu <qiuxishi@xxxxxxxxxx>]

1) move poisoned page check at the beginning of the function.
2) add page_lock to avoid unpoison clear the flag.

Signed-off-by: Xishi Qiu <qiuxishi@xxxxxxxxxx>
Signed-off-by: Jiang Liu <jiang.liu@xxxxxxxxxx>
---
 mm/memory-failure.c |   43 ++++++++++++++++++++++---------------------
 1 files changed, 22 insertions(+), 21 deletions(-)

diff --git a/mm/memory-failure.c b/mm/memory-failure.c
index 8b20278..9b74983 100644
--- a/mm/memory-failure.c
+++ b/mm/memory-failure.c
@@ -1419,18 +1419,17 @@ static int soft_offline_huge_page(struct page *page, int flags)
 	unsigned long pfn = page_to_pfn(page);
 	struct page *hpage = compound_head(page);

+	if (PageHWPoison(hpage)) {
+		pr_info("soft offline: %#lx hugepage already poisoned\n", pfn);
+		return -EBUSY;
+	}
+
 	ret = get_any_page(page, pfn, flags);
 	if (ret < 0)
 		return ret;
 	if (ret == 0)
 		goto done;

-	if (PageHWPoison(hpage)) {
-		put_page(hpage);
-		pr_info("soft offline: %#lx hugepage already poisoned\n", pfn);
-		return -EBUSY;
-	}
-
 	/* Keep page count to indicate a given hugepage is isolated. */
 	ret = migrate_huge_page(hpage, new_page, MPOL_MF_MOVE_ALL, false,
 				MIGRATE_SYNC);
@@ -1441,12 +1440,14 @@ static int soft_offline_huge_page(struct page *page, int flags)
 		return ret;
 	}
 done:
-	if (!PageHWPoison(hpage))
-		atomic_long_add(1 << compound_trans_order(hpage),
-				&mce_bad_pages);
+	/* keep elevated page count for bad page */
+	lock_page(hpage);
+	atomic_long_add(1 << compound_trans_order(hpage), &mce_bad_pages);
 	set_page_hwpoison_huge_page(hpage);
+	unlock_page(hpage);
+
 	dequeue_hwpoisoned_huge_page(hpage);
-	/* keep elevated page count for bad page */
+
 	return ret;
 }

@@ -1488,6 +1489,11 @@ int soft_offline_page(struct page *page, int flags)
 		}
 	}

+	if (PageHWPoison(page)) {
+		pr_info("soft offline: %#lx page already poisoned\n", pfn);
+		return -EBUSY;
+	}
+
 	ret = get_any_page(page, pfn, flags);
 	if (ret < 0)
 		return ret;
@@ -1519,19 +1525,11 @@ int soft_offline_page(struct page *page, int flags)
 		return -EIO;
 	}

-	lock_page(page);
-	wait_on_page_writeback(page);
-
 	/*
 	 * Synchronized using the page lock with memory_failure()
 	 */
-	if (PageHWPoison(page)) {
-		unlock_page(page);
-		put_page(page);
-		pr_info("soft offline: %#lx page already poisoned\n", pfn);
-		return -EBUSY;
-	}
-
+	lock_page(page);
+	wait_on_page_writeback(page);
 	/*
 	 * Try to invalidate first. This should work for
 	 * non dirty unmapped page cache pages.
@@ -1582,8 +1580,11 @@ int soft_offline_page(struct page *page, int flags)
 		return ret;

 done:
+	/* keep elevated page count for bad page */
+	lock_page(page);
 	atomic_long_add(1, &mce_bad_pages);
 	SetPageHWPoison(page);
-	/* keep elevated page count for bad page */
+	unlock_page(page);
+
 	return ret;
 }
-- 
1.7.1


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