syzbot

============================================
WARNING: possible recursive locking detected
5.3.0-rc6-next-20190830 #75 Not tainted
--------------------------------------------
syz-executor862/10012 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

1 lock held by syz-executor862/10012:
 #0: ffffffff8904ff60 (mmu_notifier_invalidate_range_start){+.+.}, at: __oom_reap_task_mm+0x196/0x490 mm/oom_kill.c:542

stack backtrace:
CPU: 1 PID: 10012 Comm: syz-executor862 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
 exit_mmap+0x42c/0x530 mm/mmap.c:3149
 __mmput kernel/fork.c:1082 [inline]
 mmput+0x179/0x4d0 kernel/fork.c:1103
 exit_mm kernel/exit.c:547 [inline]
 do_exit+0x823/0x2e60 kernel/exit.c:866
 do_group_exit+0x135/0x360 kernel/exit.c:983
 get_signal+0x47c/0x2500 kernel/signal.c:2734
 do_signal+0x87/0x1700 arch/x86/kernel/signal.c:815
 exit_to_usermode_loop+0x286/0x380 arch/x86/entry/common.c:159
 prepare_exit_to_usermode arch/x86/entry/common.c:194 [inline]
 syscall_return_slowpath arch/x86/entry/common.c:274 [inline]
 do_syscall_64+0x65f/0x760 arch/x86/entry/common.c:300
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x4466d9
Code: Bad RIP value.
RSP: 002b:00007f872d192db8 EFLAGS: 00000246 ORIG_RAX: 00000000000000ca
RAX: fffffffffffffe00 RBX: 00000000006dbc28 RCX: 00000000004466d9
RDX: 0000000000000000 RSI: 0000000000000080 RDI: 00000000006dbc28
RBP: 00000000006dbc20 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000006dbc2c
R13: 00007ffdda08980f R14: 00007f872d1939c0 R15: 20c49ba5e353f7cf