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authorKirill A. Shutemov <kirill.shutemov@linux.intel.com>2016-11-30 15:54:05 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2016-11-30 16:32:52 -0800
commit655548bf6271b212cd1e4c259da9dbe616348d38 (patch)
tree1fc4291a88aff486008f0f41db7c6617df9ac7af
parente1465d125d2189e667029b9fa8a6f455180fbcf2 (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>
-rw-r--r--mm/mlock.c7
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)) {