thp: fix corner case of munlock() of PTE-mapped THPs

The following program triggers BUG() in munlock_vma_pages_range():

	// autogenerated by syzkaller (http://github.com/google/syzkaller)
	#include <sys/mman.h>

	int main()
	{
	  mmap((void*)0x20105000ul, 0xc00000ul, 0x2ul, 0x2172ul, -1, 0);
	  mremap((void*)0x201fd000ul, 0x4000ul, 0xc00000ul, 0x3ul, 0x203f0000ul);
	  return 0;
	}

The test-case constructs the situation when munlock_vma_pages_range()
finds PTE-mapped THP-head in the middle of page table and, by mistake,
skips HPAGE_PMD_NR pages after that.

As result, on the next iteration it hits the middle of PMD-mapped THP
and gets upset seeing mlocked tail page.

The solution is only skip HPAGE_PMD_NR pages if the THP was mlocked
during munlock_vma_page().  It would guarantee that the page is
PMD-mapped as we never mlock PTE-mapeed THPs.

Fixes: e90309c9f772 ("thp: allow mlocked THP again")
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Kirill A. Shutemov <[email protected]>
Reported-by: Dmitry Vyukov <[email protected]>
Cc: Konstantin Khlebnikov <[email protected]>
Cc: Andrey Ryabinin <[email protected]>
Cc: syzkaller <[email protected]>
Cc: Andrea Arcangeli <[email protected]>
Cc: <[email protected]>	[4.5+]
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

0 files changed, 0 insertions, 0 deletions