INFO: rcu detected stall in umount_tree

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: 0725d4e1b8b0 Merge tag 'nfs-for-4.18-1' of git://git.linux..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=16a6fb6f800000
kernel config: https://syzkaller.appspot.com/x/.config?x=3de185e943e1d12f
dashboard link: https://syzkaller.appspot.com/bug?extid=a2e99250d6470fb3bd7b
compiler: gcc (GCC) 8.0.1 20180413 (experimental)
CC: [linux-...@vger.kernel.org linux-...@vger.kernel.org
vi...@zeniv.linux.org.uk]

Unfortunately, I don't have any reproducer for this crash yet.

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+a2e992...@syzkaller.appspotmail.com

devpts: called with bogus options
devpts: called with bogus options
INFO: rcu_sched self-detected stall on CPU
1-...!: (124998 ticks this GP) idle=082/1/4611686018427387906
softirq=419897/419897 fqs=1013
(t=125000 jiffies g=144606 c=144605 q=33)
rcu_sched kthread starved for 120948 jiffies! g144606 c144605 f0x0
RCU_GP_WAIT_FQS(3) ->state=0x0 ->cpu=1
RCU grace-period kthread stack dump:
rcu_sched R running task 22392 10 2 0x80000000
Call Trace:
context_switch kernel/sched/core.c:2858 [inline]
__schedule+0x83b/0x1e70 kernel/sched/core.c:3500
schedule+0xef/0x430 kernel/sched/core.c:3544
schedule_timeout+0x138/0x240 kernel/time/timer.c:1801
rcu_gp_kthread+0x700/0x1c80 kernel/rcu/tree.c:2179
kthread+0x345/0x410 kernel/kthread.c:240
ret_from_fork+0x3a/0x50 arch/x86/entry/entry_64.S:412
NMI backtrace for cpu 1
CPU: 1 PID: 20059 Comm: syz-executor4 Not tainted 4.17.0+ #99
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+0x1b9/0x294 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+0x237/0xcb0 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+0x3e3/0x10a0 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+0x15d/0x710 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+0x24b/0x1450 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 35
d0 aa ff 49 8d 7f 20 48 89 f9 48 c1 e9 03 42 80 3c 31 00 <0f> 85 fd 0c 00
00 48 8b 85 a0 fc ff ff 49 39 84 24 78 ff ff ff 0f
RSP: 0018:ffff8801bf937330 EFLAGS: 00000246 ORIG_RAX: ffffffffffffff13
RAX: 0000000000040000 RBX: ffff8801819f5600 RCX: 1ffff1003148d0c4
RDX: 0000000000040000 RSI: ffffffff81cf6d5b RDI: ffff88018a468620
RBP: ffff8801bf9376d0 R08: ffff8801820d4080 R09: fffffbfff1208c98
R10: fffffbfff1208c98 R11: ffffffff890464c3 R12: ffff88018a4686a8
R13: ffff8801819f56a8 R14: dffffc0000000000 R15: ffff88018a468600
umount_tree+0x738/0x1230 fs/namespace.c:1524
attach_recursive_mnt+0x906/0xb50 fs/namespace.c:2069
graft_tree+0x1aa/0x240 fs/namespace.c:2133
do_loopback fs/namespace.c:2254 [inline]
do_mount+0x277c/0x30b0 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+0x1b1/0x800 arch/x86/entry/common.c:290
entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x455b29
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:00007f77aa4e0c68 EFLAGS: 00000246 ORIG_RAX: 00000000000000a5
RAX: ffffffffffffffda RBX: 00007f77aa4e16d4 RCX: 0000000000455b29
RDX: 0000000020000180 RSI: 0000000020187ff8 RDI: 0000000020000200
RBP: 000000000072c210 R08: 00000000200e7000 R09: 0000000000000000
R10: 0000000000005010 R11: 0000000000000246 R12: 00000000ffffffff
R13: 00000000004c1e44 R14: 00000000004cf088 R15: 0000000000000005


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[syzbot]

Auto-closing this bug as obsolete.
Crashes did not happen for a while, no reproducer and no activity.