[PATCH 3.2 33/46] mm/huge_memory: replace VM_NO_THP VM_BUG_ON with actual VMA check

Ben Hutchings
2016-06-12T21:35:56Z

From: Konstantin Khlebnikov <koct9i@gmail.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@gmail.com>
Reported-by: Dmitry Vyukov <dvyukov@google.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-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@decadent.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,