rcu: INFO: rcu_preempt detected stalls on CPUs/tasks: rcu: 0-...!: (1 GPs behind) idle=dca/1/0x4000000000000000 softirq=21174/21176 fqs=3 (detected by 1, t=10502 jiffies, g=31501, q=50) ============================================ WARNING: possible recursive locking detected 5.10.0-next-20201223-syzkaller #0 Not tainted -------------------------------------------- systemd-timesyn/4985 is trying to acquire lock: ffffffff8b36b758 (rcu_node_0){-.-.}-{2:2}, at: rcu_dump_cpu_stacks+0x9c/0x21e kernel/rcu/tree_stall.h:334 but task is already holding lock: ffffffff8b36b758 (rcu_node_0){-.-.}-{2:2}, at: print_other_cpu_stall kernel/rcu/tree_stall.h:493 [inline] ffffffff8b36b758 (rcu_node_0){-.-.}-{2:2}, at: check_cpu_stall kernel/rcu/tree_stall.h:652 [inline] ffffffff8b36b758 (rcu_node_0){-.-.}-{2:2}, at: rcu_pending kernel/rcu/tree.c:3751 [inline] ffffffff8b36b758 (rcu_node_0){-.-.}-{2:2}, at: rcu_sched_clock_irq.cold+0xbc/0xec3 kernel/rcu/tree.c:2580 other info that might help us debug this: Possible unsafe locking scenario: CPU0 ---- lock(rcu_node_0); lock(rcu_node_0); *** DEADLOCK *** May be due to missing lock nesting notation 1 lock held by systemd-timesyn/4985: #0: ffffffff8b36b758 (rcu_node_0){-.-.}-{2:2}, at: print_other_cpu_stall kernel/rcu/tree_stall.h:493 [inline] #0: ffffffff8b36b758 (rcu_node_0){-.-.}-{2:2}, at: check_cpu_stall kernel/rcu/tree_stall.h:652 [inline] #0: ffffffff8b36b758 (rcu_node_0){-.-.}-{2:2}, at: rcu_pending kernel/rcu/tree.c:3751 [inline] #0: ffffffff8b36b758 (rcu_node_0){-.-.}-{2:2}, at: rcu_sched_clock_irq.cold+0xbc/0xec3 kernel/rcu/tree.c:2580 stack backtrace: CPU: 1 PID: 4985 Comm: systemd-timesyn Not tainted 5.10.0-next-20201223-syzkaller #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 Call Trace: __dump_stack lib/dump_stack.c:79 [inline] dump_stack+0x107/0x163 lib/dump_stack.c:120 print_deadlock_bug kernel/locking/lockdep.c:2761 [inline] check_deadlock kernel/locking/lockdep.c:2804 [inline] validate_chain kernel/locking/lockdep.c:3595 [inline] __lock_acquire.cold+0x15e/0x3b0 kernel/locking/lockdep.c:4832 lock_acquire kernel/locking/lockdep.c:5437 [inline] lock_acquire+0x29d/0x740 kernel/locking/lockdep.c:5402 __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline] _raw_spin_lock_irqsave+0x39/0x50 kernel/locking/spinlock.c:159 rcu_dump_cpu_stacks+0x9c/0x21e kernel/rcu/tree_stall.h:334 print_other_cpu_stall kernel/rcu/tree_stall.h:510 [inline] check_cpu_stall kernel/rcu/tree_stall.h:652 [inline] rcu_pending kernel/rcu/tree.c:3751 [inline] rcu_sched_clock_irq.cold+0x6db/0xec3 kernel/rcu/tree.c:2580 update_process_times+0x16d/0x200 kernel/time/timer.c:1782 tick_sched_handle+0x9b/0x180 kernel/time/tick-sched.c:226 tick_sched_timer+0x1b0/0x2d0 kernel/time/tick-sched.c:1376 __run_hrtimer kernel/time/hrtimer.c:1519 [inline] __hrtimer_run_queues+0x1ce/0xea0 kernel/time/hrtimer.c:1583 hrtimer_interrupt+0x334/0x940 kernel/time/hrtimer.c:1645 local_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1085 [inline] __sysvec_apic_timer_interrupt+0x146/0x540 arch/x86/kernel/apic/apic.c:1102 asm_call_irq_on_stack+0xf/0x20 __run_sysvec_on_irqstack arch/x86/include/asm/irq_stack.h:37 [inline] run_sysvec_on_irqstack_cond arch/x86/include/asm/irq_stack.h:89 [inline] sysvec_apic_timer_interrupt+0xbd/0x100 arch/x86/kernel/apic/apic.c:1096 asm_sysvec_apic_timer_interrupt+0x12/0x20 arch/x86/include/asm/idtentry.h:628 RIP: 0010:csd_lock_wait kernel/smp.c:227 [inline] RIP: 0010:smp_call_function_single+0x1c3/0x4b0 kernel/smp.c:512 Code: 08 48 89 44 24 58 e8 0c fb ff ff 41 89 c5 eb 07 e8 82 43 0b 00 f3 90 44 8b 64 24 48 31 ff 41 83 e4 01 44 89 e6 e8 ed 4a 0b 00 <45> 85 e4 75 e1 e8 63 43 0b 00 e8 5e 43 0b 00 bf 01 00 00 00 e8 b4 RSP: 0018:ffffc9000183fa00 EFLAGS: 00000246 RAX: 0000000000000000 RBX: 1ffff92000307f44 RCX: 0000000000000001 RDX: 0000000000000000 RSI: ffff88801a7f8000 RDI: 0000000000000003 RBP: ffffc9000183fac8 R08: 0000000000000000 R09: 0000000000000001 R10: ffffffff81673653 R11: 0000000000000000 R12: 0000000000000001 R13: 0000000000000000 R14: 0000000000000001 R15: 0000000000000008 smp_call_function_many_cond+0x25f/0x9d0 kernel/smp.c:648 smp_call_function_many kernel/smp.c:711 [inline] smp_call_function kernel/smp.c:733 [inline] on_each_cpu+0x4f/0x110 kernel/smp.c:832 clock_was_set+0x18/0x20 kernel/time/hrtimer.c:871 timekeeping_inject_offset+0x436/0x570 kernel/time/timekeeping.c:1375 do_adjtimex+0x28f/0xa30 kernel/time/timekeeping.c:2396 do_clock_adjtime kernel/time/posix-timers.c:1109 [inline] __do_sys_clock_adjtime+0x163/0x270 kernel/time/posix-timers.c:1121 do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46 entry_SYSCALL_64_after_hwframe+0x44/0xa9 RIP: 0033:0x7f539630e1b7 Code: 73 01 c3 48 8b 0d e1 fc 2a 00 f7 d8 64 89 01 48 83 c8 ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 b8 31 01 00 00 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 8b 0d b1 fc 2a 00 f7 d8 64 89 01 48 RSP: 002b:00007ffd2a74a568 EFLAGS: 00000246 ORIG_RAX: 0000000000000131 RAX: ffffffffffffffda RBX: 000055acdf58a630 RCX: 00007f539630e1b7 RDX: ffffffffe8b480a5 RSI: 00007ffd2a74a630 RDI: 0000000000000000 RBP: 00007ffd2a74a630 R08: 0000000000000020 R09: 000000000000000d R10: 0000000000000000 R11: 0000000000000246 R12: 00000000ffffffff R13: 00007ffd2a74a720 R14: 0000000000000004 R15: 0000000000000001