Commit 3486b85a authored Apr 28, 2016 by Konstantin Khlebnikov Committed by Linus Torvalds Apr 28, 2016

mm/huge_memory: replace VM_NO_THP VM_BUG_ON with actual VMA check

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: 78f11a25 ("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>
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent 314e9b75

mm/huge_memory.c

+2 −4

Original line number	Diff line number	Diff line
		@@ -1960,10 +1960,9 @@ int khugepaged_enter_vma_merge(struct vm_area_struct *vma,
		* 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;
		VM_BUG_ON_VMA(vm_flags & VM_NO_THP, vma);
		hstart = (vma->vm_start + ~HPAGE_PMD_MASK) & HPAGE_PMD_MASK;
		hend = vma->vm_end & HPAGE_PMD_MASK;
		if (hstart < hend)
		@@ -2352,8 +2351,7 @@ static bool hugepage_vma_check(struct vm_area_struct *vma)
		return false;
		if (is_vma_temporary_stack(vma))
		return false;
		VM_BUG_ON_VMA(vma->vm_flags & VM_NO_THP, vma);
		return true;
		return !(vma->vm_flags & VM_NO_THP);
		}

		static void collapse_huge_page(struct mm_struct *mm,

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