diff options
| author | Kirill A. Shutemov | 2016-11-30 15:54:05 -0800 |
|---|---|---|
| committer | Linus Torvalds | 2016-11-30 16:32:52 -0800 |
| commit | 655548bf6271b212cd1e4c259da9dbe616348d38 (patch) | |
| tree | 1fc4291a88aff486008f0f41db7c6617df9ac7af /mm/mlock.c | |
| parent | e1465d125d2189e667029b9fa8a6f455180fbcf2 (diff) | |
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/20161115132703.7s7rrgmwttegcdh4@black.fi.intel.com
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Reported-by: Dmitry Vyukov <dvyukov@google.com>
Cc: Konstantin Khlebnikov <koct9i@gmail.com>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: syzkaller <syzkaller@googlegroups.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: <stable@vger.kernel.org> [4.5+]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm/mlock.c')
| -rw-r--r-- | mm/mlock.c | 7 |
1 files changed, 5 insertions, 2 deletions
diff --git a/mm/mlock.c b/mm/mlock.c index 145a4258ddbc..cdbed8aaa426 100644 --- a/mm/mlock.c +++ b/mm/mlock.c @@ -190,10 +190,13 @@ unsigned int munlock_vma_page(struct page *page) */ spin_lock_irq(zone_lru_lock(zone)); - nr_pages = hpage_nr_pages(page); - if (!TestClearPageMlocked(page)) + if (!TestClearPageMlocked(page)) { + /* Potentially, PTE-mapped THP: do not skip the rest PTEs */ + nr_pages = 1; goto unlock_out; + } + nr_pages = hpage_nr_pages(page); __mod_zone_page_state(zone, NR_MLOCK, -nr_pages); if (__munlock_isolate_lru_page(page, true)) { |