linux-kernel - [PATCH 3.2 33/46] mm/huge_memory: replace VM_NO_THP VM_BUG

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Date:	Sun, 12 Jun 2016 22:34:42 +0100
From:	Ben Hutchings <ben@...adent.org.uk>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:	akpm@...ux-foundation.org,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	"Linus Torvalds" <torvalds@...ux-foundation.org>,
	"Konstantin Khlebnikov" <koct9i@...il.com>,
	"Vlastimil Babka" <vbabka@...e.cz>,
	"Dmitry Vyukov" <dvyukov@...gle.com>,
	"Andrea Arcangeli" <aarcange@...hat.com>
Subject: [PATCH 3.2 33/46] mm/huge_memory: replace VM_NO_THP VM_BUG_ON
 with actual VMA check

3.2.81-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Konstantin Khlebnikov <koct9i@...il.com>

commit 3486b85a29c1741db99d0c522211c82d2b7a56d0 upstream.

Khugepaged detects own VMAs by checking vm_file and vm_ops but this way
it cannot distinguish private /dev/zero mappings from other special
mappings like /dev/hpet which has no vm_ops and popultes PTEs in mmap.

This fixes false-positive VM_BUG_ON and prevents installing THP where
they are not expected.

Link: http://lkml.kernel.org/r/CACT4Y+ZmuZMV5CjSFOeXviwQdABAgT7T+StKfTqan9YDtgEi5g@mail.gmail.com
Fixes: 78f11a255749 ("mm: thp: fix /dev/zero MAP_PRIVATE and vm_flags cleanups")
Signed-off-by: Konstantin Khlebnikov <koct9i@...il.com>
Reported-by: Dmitry Vyukov <dvyukov@...gle.com>
Acked-by: Vlastimil Babka <vbabka@...e.cz>
Acked-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
Cc: Dmitry Vyukov <dvyukov@...gle.com>
Cc: Andrea Arcangeli <aarcange@...hat.com>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
[bwh: Backported to 3.2:
 - The assertions use VM_BUG_ON() and also check is_linear_pfn_mapping();
   keep that check
 - Adjust context]
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 mm/huge_memory.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1635,14 +1635,14 @@ int khugepaged_enter_vma_merge(struct vm
 		 * page fault if needed.
 		 */
 		return 0;
-	if (vma->vm_ops)
+	if (vma->vm_ops || (vm_flags & VM_NO_THP))
 		/* khugepaged not yet working on file or special mappings */
 		return 0;
 	/*
 	 * If is_pfn_mapping() is true is_learn_pfn_mapping() must be
 	 * true too, verify it here.
 	 */
-	VM_BUG_ON(is_linear_pfn_mapping(vma) || vm_flags & VM_NO_THP);
+	VM_BUG_ON(is_linear_pfn_mapping(vma));
 	hstart = (vma->vm_start + ~HPAGE_PMD_MASK) & HPAGE_PMD_MASK;
 	hend = vma->vm_end & HPAGE_PMD_MASK;
 	if (hstart < hend)
@@ -1831,8 +1831,8 @@ static bool hugepage_vma_check(struct vm
 	 * If is_pfn_mapping() is true is_learn_pfn_mapping() must be
 	 * true too, verify it here.
 	 */
-	VM_BUG_ON(is_linear_pfn_mapping(vma) || vma->vm_flags & VM_NO_THP);
-	return true;
+	VM_BUG_ON(is_linear_pfn_mapping(vma));
+	return !(vma->vm_flags & VM_NO_THP);
 }
 
 static void collapse_huge_page(struct mm_struct *mm,