[PATCH 3/6] mm/hwpoison: fix num_poisoned_pages error statistics for thp

[Wanpeng Li <liwanp@linux.vnet.ibm.com>]

There is a race between hwpoison page and unpoison page, memory_failure 
set the page hwpoison and increase num_poisoned_pages without hold page 
lock, and one page count will be accounted against thp for num_poisoned_pages.
However, unpoison can occur before memory_failure hold page lock and 
split transparent hugepage, unpoison will decrease num_poisoned_pages 
by 1 << compound_order since memory_failure has not yet split transparent 
hugepage with page lock held. That means we account one page for hwpoison
and 1 << compound_order for unpoison. This patch fix it by decrease one 
account for num_poisoned_pages against no hugetlbfs pages case.

Signed-off-by: Wanpeng Li <liwanp@linux.vnet.ibm.com>
---
 mm/memory-failure.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/memory-failure.c b/mm/memory-failure.c
index 5092e06..6bfd51e 100644
--- a/mm/memory-failure.c
+++ b/mm/memory-failure.c
@@ -1350,7 +1350,7 @@ int unpoison_memory(unsigned long pfn)
 			return 0;
 		}
 		if (TestClearPageHWPoison(p))
-			atomic_long_sub(nr_pages, &num_poisoned_pages);
+			atomic_long_dec(&num_poisoned_pages);
 		pr_info("MCE: Software-unpoisoned free page %#lx\n", pfn);
 		return 0;
 	}
-- 
1.8.1.2