syzbot

rcu: INFO: rcu_preempt self-detected stall on CPU
rcu: 	0-....: (1 GPs behind) idle=68e/1/0x4000000000000002 softirq=80268/80269 fqs=5235 
rcu: 	 (t=10500 jiffies g=117465 q=1559)
NMI backtrace for cpu 0
CPU: 0 PID: 5262 Comm: syz-executor4 Not tainted 4.19.0+ #300
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+0x244/0x39d lib/dump_stack.c:113
 nmi_cpu_backtrace.cold.1+0x5c/0xa1 lib/nmi_backtrace.c:101
 nmi_trigger_cpumask_backtrace+0x1b3/0x1ed 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:162 [inline]
 rcu_dump_cpu_stacks+0x16f/0x1bc kernel/rcu/tree.c:1195
 print_cpu_stall.cold.67+0x1f3/0x3c7 kernel/rcu/tree.c:1334
 check_cpu_stall kernel/rcu/tree.c:1408 [inline]
 rcu_pending kernel/rcu/tree.c:2961 [inline]
 rcu_check_callbacks+0xf3b/0x13f0 kernel/rcu/tree.c:2506
 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+0x41c/0x10d0 kernel/time/hrtimer.c:1460
 hrtimer_interrupt+0x313/0x780 kernel/time/hrtimer.c:1518
 local_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1034 [inline]
 smp_apic_timer_interrupt+0x1a1/0x760 arch/x86/kernel/apic/apic.c:1059
 apic_timer_interrupt+0xf/0x20 arch/x86/entry/entry_64.S:801
 </IRQ>
RIP: 0010:arch_atomic_try_cmpxchg arch/x86/include/asm/atomic.h:200 [inline]
RIP: 0010:atomic_try_cmpxchg include/asm-generic/atomic-instrumented.h:73 [inline]
RIP: 0010:refcount_inc_not_zero_checked+0x195/0x2f0 lib/refcount.c:131
Code: 00 00 00 4c 89 e7 e8 6a ed 33 fe 48 8b bd 30 ff ff ff be 04 00 00 00 e8 39 ed 33 fe 48 8b 85 28 ff ff ff 0f b6 00 84 c0 74 08 <3c> 03 0f 8e 32 01 00 00 45 8b 75 80 44 89 f0 f0 41 0f b1 1c 24 41
RSP: 0018:ffff880180eaf390 EFLAGS: 00000202 ORIG_RAX: ffffffffffffff13
RAX: 0000000000000004 RBX: 0000000000000002 RCX: ffffffff838f7fa7
RDX: 0000000000000000 RSI: 0000000000000004 RDI: ffff880180eaf3c8
RBP: ffff880180eaf470 R08: ffffed00301d5e7a R09: ffffed00301d5e79
R10: ffffed00301d5e79 R11: 0000000000000003 R12: ffff8801d8c1c040
R13: ffff880180eaf448 R14: 0000000000000001 R15: 1ffff100301d5e79
 refcount_inc_checked+0x15/0x70 lib/refcount.c:153
 nfs_match_client fs/nfs/client.c:303 [inline]
 nfs_get_client+0x971/0x14c0 fs/nfs/client.c:413
 nfs_init_server+0x357/0xff0 fs/nfs/client.c:670
 nfs_create_server+0x86/0x5f0 fs/nfs/client.c:954
 nfs_try_mount+0x180/0xa80 fs/nfs/super.c:1884
 nfs_fs_mount+0x17f8/0x2f1c fs/nfs/super.c:2695
 mount_fs+0xae/0x31d fs/super.c:1261
 vfs_kern_mount.part.35+0xdc/0x4f0 fs/namespace.c:961
 vfs_kern_mount fs/namespace.c:951 [inline]
 do_new_mount fs/namespace.c:2457 [inline]
 do_mount+0x581/0x31f0 fs/namespace.c:2789
 ksys_mount+0x12d/0x140 fs/namespace.c:3005
 __do_sys_mount fs/namespace.c:3019 [inline]
 __se_sys_mount fs/namespace.c:3016 [inline]
 __x64_sys_mount+0xbe/0x150 fs/namespace.c:3016
 do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x457569
Code: fd b3 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 cb b3 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007f657ec61c78 EFLAGS: 00000246 ORIG_RAX: 00000000000000a5
RAX: ffffffffffffffda RBX: 0000000000000005 RCX: 0000000000457569
RDX: 0000000020fb5ffc RSI: 0000000020343ff8 RDI: 0000000020000080
RBP: 000000000072bf00 R08: 000000002000a000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007f657ec626d4
R13: 00000000004c289b R14: 00000000004d3c78 R15: 00000000ffffffff
sched: RT throttling activated