4.8-stable review patch. If anyone has any objections, please let me know.
------------------
From: Kirill A. Shutemov <kirill.shute...@linux.intel.com>
commit 655548bf6271b212cd1e4c259da9dbe616348d38 upstream.
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/20161115132703.7s7rrgmwttegc...@black.fi.intel.com
Signed-off-by: Kirill A. Shutemov <kirill.shute...@linux.intel.com>
Reported-by: Dmitry Vyukov <dvyu...@google.com>
Cc: Konstantin Khlebnikov <koc...@gmail.com>
Cc: Andrey Ryabinin <aryabi...@virtuozzo.com>
Cc: syzkaller <syzkal...@googlegroups.com>
Cc: Andrea Arcangeli <aarca...@redhat.com>
Signed-off-by: Andrew Morton <a...@linux-foundation.org>
Signed-off-by: Linus Torvalds <torva...@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>
---
mm/mlock.c | 7 +++++--
1 file changed, 5 insertions(+), 2 deletions(-)
--- a/mm/mlock.c
+++ b/mm/mlock.c
@@ -190,10 +190,13 @@ unsigned int munlock_vma_page(struct pag
*/
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)) {
