[PATCH] mm/memory-failure.c: fix memory leak by race between poison and unpoison

[Naoya Horiguchi]

When a memory error happens on an in-use page or (free and in-use) hugepage,
the victim page is isolated with its refcount set to one. When you try to
unpoison it later, unpoison_memory() calls put_page() for it twice in order to
bring the page back to free page pool (buddy or free hugepage list.)
However, if another memory error occurs on the page which we are unpoisoning,
memory_failure() returns without releasing the refcount which was incremented
in the same call at first, which results in memory leak and unconsistent
num_poisoned_pages statistics. This patch fixes it.

Signed-off-by: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>    [2.6.32+]
---
 mm/memory-failure.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git next-20140512.orig/mm/memory-failure.c next-20140512/mm/memory-failure.c
index 9872af1b1e9d..93a08bd78c78 100644
--- next-20140512.orig/mm/memory-failure.c
+++ next-20140512/mm/memory-failure.c
@@ -1153,6 +1153,8 @@ int memory_failure(unsigned long pfn, int trapno, int flags)
 	 */
 	if (!PageHWPoison(p)) {
 		printk(KERN_ERR "MCE %#lx: just unpoisoned\n", pfn);
+		atomic_long_sub(nr_pages, &num_poisoned_pages);
+		put_page(hpage);
 		res = 0;
 		goto out;
 	}
-- 
1.9.0

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