[3.11.y.z extended stable] Patch "mm/memory-failure.c: fix memory leak by race between poison and unpoison" has been added to staging queue

[Luis Henriques]

This is a note to let you know that I have just added a patch titled

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

to the linux-3.11.y-queue branch of the 3.11.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.11.y-queue

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.11.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Luis

------

>From e402a49c201f9945b8d4c766fb41c736a28a6e5a Mon Sep 17 00:00:00 2001
From: Naoya Horiguchi <n-horiguchi at ah.jp.nec.com>
Date: Thu, 22 May 2014 11:54:21 -0700
Subject: mm/memory-failure.c: fix memory leak by race between poison and
 unpoison

commit 3e030ecc0fc7de10fd0da10c1c19939872a31717 upstream.

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 at ah.jp.nec.com>
Cc: Andi Kleen <andi at firstfloor.org>
Signed-off-by: Andrew Morton <akpm at linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds at linux-foundation.org>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 mm/memory-failure.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/mm/memory-failure.c b/mm/memory-failure.c
index d3772a6118ee..9a5150d2e937 100644
--- a/mm/memory-failure.c
+++ b/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;
 	}
--
1.9.1