syzbot

INFO: rcu_sched self-detected stall on CPU
	1-...!: (104999 ticks this GP) idle=cce/1/4611686018427387906 softirq=173030/173030 fqs=959 
	 (t=105000 jiffies g=86005 c=86004 q=68)
rcu_sched kthread starved for 101155 jiffies! g86005 c86004 f0x0 RCU_GP_WAIT_FQS(3) ->state=0x0 ->cpu=1
RCU grace-period kthread stack dump:
rcu_sched       R  running task    23392    10      2 0x80000000
Call Trace:
 context_switch kernel/sched/core.c:2853 [inline]
 __schedule+0x87c/0x1ed0 kernel/sched/core.c:3501
 schedule+0xfb/0x450 kernel/sched/core.c:3545
 schedule_timeout+0x140/0x260 kernel/time/timer.c:1801
 rcu_gp_kthread+0x717/0x1c90 kernel/rcu/tree.c:2179
 kthread+0x345/0x410 kernel/kthread.c:246
 ret_from_fork+0x3a/0x50 arch/x86/entry/entry_64.S:412
NMI backtrace for cpu 1
CPU: 1 PID: 840 Comm: syz-executor3 Not tainted 4.18.0-rc5+ #152
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
 <IRQ>
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0x1c9/0x2b4 lib/dump_stack.c:113
 nmi_cpu_backtrace.cold.4+0x19/0xce lib/nmi_backtrace.c:103
 nmi_trigger_cpumask_backtrace+0x151/0x192 lib/nmi_backtrace.c:62
 arch_trigger_cpumask_backtrace+0x14/0x20 arch/x86/kernel/apic/hw_nmi.c:38
 trigger_single_cpu_backtrace include/linux/nmi.h:156 [inline]
 rcu_dump_cpu_stacks+0x175/0x1c2 kernel/rcu/tree.c:1336
 print_cpu_stall kernel/rcu/tree.c:1485 [inline]
 check_cpu_stall.isra.60.cold.78+0x36c/0x5a6 kernel/rcu/tree.c:1553
 __rcu_pending kernel/rcu/tree.c:3244 [inline]
 rcu_pending kernel/rcu/tree.c:3291 [inline]
 rcu_check_callbacks+0x23f/0xcd0 kernel/rcu/tree.c:2646
 update_process_times+0x2d/0x70 kernel/time/timer.c:1636
 tick_sched_handle+0x9f/0x180 kernel/time/tick-sched.c:164
 tick_sched_timer+0x45/0x130 kernel/time/tick-sched.c:1274
 __run_hrtimer kernel/time/hrtimer.c:1398 [inline]
 __hrtimer_run_queues+0x3eb/0x10c0 kernel/time/hrtimer.c:1460
 hrtimer_interrupt+0x2f3/0x750 kernel/time/hrtimer.c:1518
 local_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1025 [inline]
 smp_apic_timer_interrupt+0x165/0x730 arch/x86/kernel/apic/apic.c:1050
 apic_timer_interrupt+0xf/0x20 arch/x86/entry/entry_64.S:863
 </IRQ>
RIP: 0010:do_make_slave fs/pnode.c:101 [inline]
RIP: 0010:change_mnt_propagation+0x253/0x1470 fs/pnode.c:128
Code: 89 e7 4c 89 a5 98 fc ff ff 49 be 00 00 00 00 00 fc ff df eb 30 e8 0d d4 a9 ff 49 8d 7f 20 48 89 f9 48 c1 e9 03 42 80 3c 31 00 <0f> 85 10 0d 00 00 48 8b 85 a0 fc ff ff 49 39 84 24 78 ff ff ff 0f 
RSP: 0018:ffff8801988ef330 EFLAGS: 00000246 ORIG_RAX: ffffffffffffff13
RAX: 0000000000040000 RBX: ffff88019398f200 RCX: 1ffff1003ae11904
RDX: 0000000000040000 RSI: ffffffff81d23753 RDI: ffff8801d708c820
RBP: ffff8801988ef6d0 R08: ffff88019a9f8240 R09: fffffbfff12090f8
R10: fffffbfff12090f8 R11: ffffffff890487c3 R12: ffff8801d708c8a8
R13: ffff88019398f2a8 R14: dffffc0000000000 R15: ffff8801d708c800
 umount_tree+0x758/0x1270 fs/namespace.c:1524
 attach_recursive_mnt+0x91a/0xb70 fs/namespace.c:2069
 graft_tree+0x1aa/0x240 fs/namespace.c:2133
 do_loopback fs/namespace.c:2254 [inline]
 do_mount+0x279a/0x30e0 fs/namespace.c:2842
 ksys_mount+0x12d/0x140 fs/namespace.c:3064
 __do_sys_mount fs/namespace.c:3078 [inline]
 __se_sys_mount fs/namespace.c:3075 [inline]
 __x64_sys_mount+0xbe/0x150 fs/namespace.c:3075
 do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x455ab9
Code: 1d ba fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 0f 83 eb b9 fb ff c3 66 2e 0f 1f 84 00 00 00 00 
RSP: 002b:00007ff5bd84cc68 EFLAGS: 00000246 ORIG_RAX: 00000000000000a5
RAX: ffffffffffffffda RBX: 00007ff5bd84d6d4 RCX: 0000000000455ab9
RDX: 0000000020000180 RSI: 0000000020000040 RDI: 0000000020000280
RBP: 000000000072bff0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000001000 R11: 0000000000000246 R12: 00000000ffffffff
R13: 00000000004c01fb R14: 00000000004cfe38 R15: 0000000000000002