[3.11.y.z extended stable] Patch "hwpoison, hugetlb: lock_page/unlock_page does not match for handling a free hugepage" has been added to staging queue

[Luis Henriques]

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

    hwpoison, hugetlb: lock_page/unlock_page does not match for handling a free hugepage

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 f9611d3c3922f3da1ba4ce1bcd3ad943840ed322 Mon Sep 17 00:00:00 2001
From: Chen Yucong <slaoub at gmail.com>
Date: Thu, 22 May 2014 11:54:15 -0700
Subject: hwpoison, hugetlb: lock_page/unlock_page does not match for handling
 a free hugepage

commit b985194c8c0a130ed155b71662e39f7eaea4876f upstream.

For handling a free hugepage in memory failure, the race will happen if
another thread hwpoisoned this hugepage concurrently.  So we need to
check PageHWPoison instead of !PageHWPoison.

If hwpoison_filter(p) returns true or a race happens, then we need to
unlock_page(hpage).

Signed-off-by: Chen Yucong <slaoub at gmail.com>
Reviewed-by: Naoya Horiguchi <n-horiguchi at ah.jp.nec.com>
Tested-by: Naoya Horiguchi <n-horiguchi at ah.jp.nec.com>
Reviewed-by: Andi Kleen <ak at linux.intel.com>
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 | 15 ++++++++-------
 1 file changed, 8 insertions(+), 7 deletions(-)

diff --git a/mm/memory-failure.c b/mm/memory-failure.c
index a86908134a8f..d3772a6118ee 100644
--- a/mm/memory-failure.c
+++ b/mm/memory-failure.c
@@ -1083,15 +1083,16 @@ int memory_failure(unsigned long pfn, int trapno, int flags)
 			return 0;
 		} else if (PageHuge(hpage)) {
 			/*
-			 * Check "just unpoisoned", "filter hit", and
-			 * "race with other subpage."
+			 * Check "filter hit" and "race with other subpage."
 			 */
 			lock_page(hpage);
-			if (!PageHWPoison(hpage)
-			    || (hwpoison_filter(p) && TestClearPageHWPoison(p))
-			    || (p != hpage && TestSetPageHWPoison(hpage))) {
-				atomic_long_sub(nr_pages, &num_poisoned_pages);
-				return 0;
+			if (PageHWPoison(hpage)) {
+				if ((hwpoison_filter(p) && TestClearPageHWPoison(p))
+				    || (p != hpage && TestSetPageHWPoison(hpage))) {
+					atomic_long_sub(nr_pages, &num_poisoned_pages);
+					unlock_page(hpage);
+					return 0;
+				}
 			}
 			set_page_hwpoison_huge_page(hpage);
 			res = dequeue_hwpoisoned_huge_page(hpage);
--
1.9.1