[3.16.y-ckt stable] Patch "mm/hugetlb: add migration entry check in __unmap_hugepage_range" 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/hugetlb: add migration entry check in __unmap_hugepage_range

to the linux-3.16.y-queue branch of the 3.16.y-ckt extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.16.y-queue

This patch is scheduled to be released in version 3.16.7-ckt8.

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

For more information about the 3.16.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Luis

------

>From dea8682d8709e1858951392a0f1f35fe7ceb3bb5 Mon Sep 17 00:00:00 2001
From: Naoya Horiguchi <n-horiguchi at ah.jp.nec.com>
Date: Wed, 11 Feb 2015 15:25:32 -0800
Subject: mm/hugetlb: add migration entry check in __unmap_hugepage_range

commit 9fbc1f635fd0bd28cb32550211bf095753ac637a upstream.

If __unmap_hugepage_range() tries to unmap the address range over which
hugepage migration is on the way, we get the wrong page because pte_page()
doesn't work for migration entries.  This patch simply clears the pte for
migration entries as we do for hwpoison entries.

Fixes: 290408d4a2 ("hugetlb: hugepage migration core")
Signed-off-by: Naoya Horiguchi <n-horiguchi at ah.jp.nec.com>
Cc: Hugh Dickins <hughd at google.com>
Cc: James Hogan <james.hogan at imgtec.com>
Cc: David Rientjes <rientjes at google.com>
Cc: Mel Gorman <mel at csn.ul.ie>
Cc: Johannes Weiner <hannes at cmpxchg.org>
Cc: Michal Hocko <mhocko at suse.cz>
Cc: Rik van Riel <riel at redhat.com>
Cc: Andrea Arcangeli <aarcange at redhat.com>
Cc: Luiz Capitulino <lcapitulino at redhat.com>
Cc: Nishanth Aravamudan <nacc at linux.vnet.ibm.com>
Cc: Lee Schermerhorn <lee.schermerhorn at hp.com>
Cc: Steve Capper <steve.capper at linaro.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/hugetlb.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 5aab37914cbd..5f217e906ff9 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -2660,9 +2660,10 @@ again:
 			goto unlock;

 		/*
-		 * HWPoisoned hugepage is already unmapped and dropped reference
+		 * Migrating hugepage or HWPoisoned hugepage is already
+		 * unmapped and its refcount is dropped, so just clear pte here.
 		 */
-		if (unlikely(is_hugetlb_entry_hwpoisoned(pte))) {
+		if (unlikely(!pte_present(pte))) {
 			huge_pte_clear(mm, address, ptep);
 			goto unlock;
 		}