From: Minchan Kim <minchan@kernel.org>
Date: Thu, 22 Oct 2015 20:32:19 +0000 (-0700)
Subject: thp: use is_zero_pfn() only after pte_present() check
X-Git-Tag: v4.1.12-92~201^2~65
X-Git-Url: https://www.infradead.org/git/?a=commitdiff_plain;h=3a44a401dbee902772c2356c61fe5f7a287dc806;p=users%2Fjedix%2Flinux-maple.git

thp: use is_zero_pfn() only after pte_present() check

Orabug: 22623830

commit 47aee4d8e314384807e98b67ade07f6da476aa75 upstream.

Use is_zero_pfn() on pteval only after pte_present() check on pteval
(It might be better idea to introduce is_zero_pte() which checks
pte_present() first).

Otherwise when working on a swap or migration entry and if pte_pfn's
result is equal to zero_pfn by chance, we lose user's data in
__collapse_huge_page_copy().  So if you're unlucky, the application
segfaults and finally you could see below message on exit:

BUG: Bad rss-counter state mm:ffff88007f099300 idx:2 val:3

Fixes: ca0984caa823 ("mm: incorporate zero pages into transparent huge pages")
Signed-off-by: Minchan Kim <minchan@kernel.org>
Reviewed-by: Andrea Arcangeli <aarcange@redhat.com>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Mel Gorman <mgorman@suse.de>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Hugh Dickins <hughd@google.com>
Cc: Rik van Riel <riel@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

(cherry picked from commit dc14f050d2a7bd60b32179f842a72e376cfd467b)
Signed-off-by: Dan Duval <dan.duval@oracle.com>
---

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 078832cf36365..8e792ec5e84c6 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -2137,7 +2137,8 @@ static int __collapse_huge_page_isolate(struct vm_area_struct *vma,
 	for (_pte = pte; _pte < pte+HPAGE_PMD_NR;
 	     _pte++, address += PAGE_SIZE) {
 		pte_t pteval = *_pte;
-		if (pte_none(pteval) || is_zero_pfn(pte_pfn(pteval))) {
+		if (pte_none(pteval) || (pte_present(pteval) &&
+			is_zero_pfn(pte_pfn(pteval)))) {
 			if (++none_or_zero <= khugepaged_max_ptes_none)
 				continue;
 			else