============================================
WARNING: possible recursive locking detected
5.3.0-rc6-next-20190830 #75 Not tainted
--------------------------------------------
oom_reaper/1065 is trying to acquire lock:
ffffffff8904ff60 (mmu_notifier_invalidate_range_start){+.+.}, at: __mmu_notifier_invalidate_range_end+0x0/0x360 mm/mmu_notifier.c:169

but task is already holding lock:
ffffffff8904ff60 (mmu_notifier_invalidate_range_start){+.+.}, at: __oom_reap_task_mm+0x196/0x490 mm/oom_kill.c:542

other info that might help us debug this:
 Possible unsafe locking scenario:

       CPU0
       ----
  lock(mmu_notifier_invalidate_range_start);
  lock(mmu_notifier_invalidate_range_start);

 *** DEADLOCK ***

 May be due to missing lock nesting notation

2 locks held by oom_reaper/1065:
 #0: ffff888040a81390 (&mm->mmap_sem#2){++++}, at: oom_reap_task_mm mm/oom_kill.c:570 [inline]
 #0: ffff888040a81390 (&mm->mmap_sem#2){++++}, at: oom_reap_task mm/oom_kill.c:613 [inline]
 #0: ffff888040a81390 (&mm->mmap_sem#2){++++}, at: oom_reaper+0x3a7/0x1320 mm/oom_kill.c:651
 #1: ffffffff8904ff60 (mmu_notifier_invalidate_range_start){+.+.}, at: __oom_reap_task_mm+0x196/0x490 mm/oom_kill.c:542

stack backtrace:
CPU: 1 PID: 1065 Comm: oom_reaper Not tainted 5.3.0-rc6-next-20190830 #75
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0x172/0x1f0 lib/dump_stack.c:113
 print_deadlock_bug kernel/locking/lockdep.c:2371 [inline]
 check_deadlock kernel/locking/lockdep.c:2412 [inline]
 validate_chain kernel/locking/lockdep.c:2955 [inline]
 __lock_acquire.cold+0x15d/0x385 kernel/locking/lockdep.c:3955
 lock_acquire+0x190/0x410 kernel/locking/lockdep.c:4487
 __mmu_notifier_invalidate_range_end+0x3c/0x360 mm/mmu_notifier.c:193
 mmu_notifier_invalidate_range_end include/linux/mmu_notifier.h:375 [inline]
 __oom_reap_task_mm+0x3fa/0x490 mm/oom_kill.c:552
 oom_reap_task_mm mm/oom_kill.c:589 [inline]
 oom_reap_task mm/oom_kill.c:613 [inline]
 oom_reaper+0x2b2/0x1320 mm/oom_kill.c:651
 kthread+0x361/0x430 kernel/kthread.c:255
 ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:352
oom_reaper: reaped process 24203 (syz-executor.2), now anon-rss:0kB, file-rss:34936kB, shmem-rss:0kB