rcu: INFO: rcu_preempt detected stalls on CPUs/tasks: rcu: 1-...!: (1 GPs behind) idle=d3a/1/0x4000000000000000 softirq=17743/17744 fqs=4 (detected by 0, t=10502 jiffies, g=24205, q=58) ============================================ WARNING: possible recursive locking detected 5.12.0-rc6-next-20210409-syzkaller #0 Not tainted -------------------------------------------- systemd-timesyn/4943 is trying to acquire lock: ffffffff8bf7de58 (rcu_node_0){-.-.}-{2:2}, at: rcu_dump_cpu_stacks+0xd0/0x3f0 kernel/rcu/tree_stall.h:336 but task is already holding lock: ffffffff8bf7de58 (rcu_node_0){-.-.}-{2:2}, at: print_other_cpu_stall kernel/rcu/tree_stall.h:542 [inline] ffffffff8bf7de58 (rcu_node_0){-.-.}-{2:2}, at: check_cpu_stall kernel/rcu/tree_stall.h:708 [inline] ffffffff8bf7de58 (rcu_node_0){-.-.}-{2:2}, at: rcu_pending kernel/rcu/tree.c:3889 [inline] ffffffff8bf7de58 (rcu_node_0){-.-.}-{2:2}, at: rcu_sched_clock_irq+0xc63/0x2080 kernel/rcu/tree.c:2628 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/4943: #0: ffffffff8bf7de58 (rcu_node_0){-.-.}-{2:2}, at: print_other_cpu_stall kernel/rcu/tree_stall.h:542 [inline] #0: ffffffff8bf7de58 (rcu_node_0){-.-.}-{2:2}, at: check_cpu_stall kernel/rcu/tree_stall.h:708 [inline] #0: ffffffff8bf7de58 (rcu_node_0){-.-.}-{2:2}, at: rcu_pending kernel/rcu/tree.c:3889 [inline] #0: ffffffff8bf7de58 (rcu_node_0){-.-.}-{2:2}, at: rcu_sched_clock_irq+0xc63/0x2080 kernel/rcu/tree.c:2628 stack backtrace: CPU: 0 PID: 4943 Comm: systemd-timesyn Not tainted 5.12.0-rc6-next-20210409-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+0x141/0x1d7 lib/dump_stack.c:120 print_deadlock_bug kernel/locking/lockdep.c:2831 [inline] check_deadlock kernel/locking/lockdep.c:2874 [inline] validate_chain kernel/locking/lockdep.c:3663 [inline] __lock_acquire.cold+0x22f/0x3b4 kernel/locking/lockdep.c:4902 lock_acquire kernel/locking/lockdep.c:5512 [inline] lock_acquire+0x1ab/0x740 kernel/locking/lockdep.c:5477 __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+0xd0/0x3f0 kernel/rcu/tree_stall.h:336 print_other_cpu_stall kernel/rcu/tree_stall.h:560 [inline] check_cpu_stall kernel/rcu/tree_stall.h:708 [inline] rcu_pending kernel/rcu/tree.c:3889 [inline] rcu_sched_clock_irq+0x1a79/0x2080 kernel/rcu/tree.c:2628 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:1373 __run_hrtimer kernel/time/hrtimer.c:1537 [inline] __hrtimer_run_queues+0x1c0/0xe50 kernel/time/hrtimer.c:1601 hrtimer_interrupt+0x330/0xa00 kernel/time/hrtimer.c:1663 local_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1089 [inline] __sysvec_apic_timer_interrupt+0x146/0x540 arch/x86/kernel/apic/apic.c:1106 sysvec_apic_timer_interrupt+0x8e/0xc0 arch/x86/kernel/apic/apic.c:1100 asm_sysvec_apic_timer_interrupt+0x12/0x20 arch/x86/include/asm/idtentry.h:632 RIP: 0010:check_kcov_mode+0x2c/0x40 kernel/kcov.c:174 Code: 05 c9 c7 8d 7e 89 c2 81 e2 00 01 00 00 a9 00 01 ff 00 74 10 31 c0 85 d2 74 15 8b 96 3c 15 00 00 85 d2 74 0b 8b 86 18 15 00 00 <39> f8 0f 94 c0 c3 66 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 00 31 c0 RSP: 0018:ffffc90000f0fab0 EFLAGS: 00000246 RAX: 0000000000000000 RBX: ffff8880b9d3a760 RCX: 0000000000000001 RDX: 0000000000000000 RSI: ffff88801c469c80 RDI: 0000000000000003 RBP: 0000000000000003 R08: 0000000000000000 R09: 0000000000000001 R10: ffffffff8168f666 R11: 0000000000000000 R12: ffffed10173a74ed R13: 0000000000000001 R14: ffff8880b9d3a768 R15: 0000000000000001 write_comp_data kernel/kcov.c:218 [inline] __sanitizer_cov_trace_const_cmp4+0x1c/0x70 kernel/kcov.c:284 csd_lock_wait kernel/smp.c:440 [inline] smp_call_function_many_cond+0x476/0xc20 kernel/smp.c:967 on_each_cpu_cond_mask+0x56/0xa0 kernel/smp.c:1133 on_each_cpu include/linux/smp.h:71 [inline] clock_was_set+0x21/0x30 kernel/time/hrtimer.c:889 timekeeping_inject_offset+0x4af/0x620 kernel/time/timekeeping.c:1375 do_adjtimex+0x28f/0xa30 kernel/time/timekeeping.c:2406 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+0x44/0xae RIP: 0033:0x7f83b1c4f1b7 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:00007ffd78cb4018 EFLAGS: 00000246 ORIG_RAX: 0000000000000131 RAX: ffffffffffffffda RBX: 00005644f7720630 RCX: 00007f83b1c4f1b7 RDX: ffffffffe93bddb8 RSI: 00007ffd78cb40e0 RDI: 0000000000000000 RBP: 00007ffd78cb40e0 R08: 0000000000000020 R09: 000000000000000d R10: 0000000000000000 R11: 0000000000000246 R12: 00000000ffffffff R13: 00007ffd78cb41d0 R14: 0000000000000003 R15: 0000000000000001