rcu: INFO: rcu_preempt detected stalls on CPUs/tasks: rcu: 0-....: (1 GPs behind) idle=5de/1/0x4000000000000000 softirq=172161/172162 fqs=5242 (detected by 1, t=10502 jiffies, g=333217, q=682) ============================================ WARNING: possible recursive locking detected 5.10.0-syzkaller #0 Not tainted -------------------------------------------- swapper/1/0 is trying to acquire lock: ffffffff8b367098 (rcu_node_0){-.-.}-{2:2}, at: rcu_dump_cpu_stacks+0x9c/0x21e kernel/rcu/tree_stall.h:334 but task is already holding lock: ffffffff8b367098 (rcu_node_0){-.-.}-{2:2}, at: print_other_cpu_stall kernel/rcu/tree_stall.h:493 [inline] ffffffff8b367098 (rcu_node_0){-.-.}-{2:2}, at: check_cpu_stall kernel/rcu/tree_stall.h:652 [inline] ffffffff8b367098 (rcu_node_0){-.-.}-{2:2}, at: rcu_pending kernel/rcu/tree.c:3751 [inline] ffffffff8b367098 (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 swapper/1/0: #0: ffffffff8b367098 (rcu_node_0){-.-.}-{2:2}, at: print_other_cpu_stall kernel/rcu/tree_stall.h:493 [inline] #0: ffffffff8b367098 (rcu_node_0){-.-.}-{2:2}, at: check_cpu_stall kernel/rcu/tree_stall.h:652 [inline] #0: ffffffff8b367098 (rcu_node_0){-.-.}-{2:2}, at: rcu_pending kernel/rcu/tree.c:3751 [inline] #0: ffffffff8b367098 (rcu_node_0){-.-.}-{2:2}, at: rcu_sched_clock_irq.cold+0xbc/0xec3 kernel/rcu/tree.c:2580 stack backtrace: CPU: 1 PID: 0 Comm: swapper/1 Not tainted 5.10.0-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:native_save_fl arch/x86/include/asm/irqflags.h:29 [inline] RIP: 0010:arch_local_save_flags arch/x86/include/asm/irqflags.h:79 [inline] RIP: 0010:arch_irqs_disabled arch/x86/include/asm/irqflags.h:169 [inline] RIP: 0010:acpi_safe_halt drivers/acpi/processor_idle.c:111 [inline] RIP: 0010:acpi_idle_do_entry+0x1c9/0x250 drivers/acpi/processor_idle.c:516 Code: 3d b6 85 f8 84 db 75 ac e8 b4 af 85 f8 e8 7f 7f 8b f8 e9 0c 00 00 00 e8 a5 af 85 f8 0f 00 2d ce 81 bd 00 e8 99 af 85 f8 fb f4 <9c> 5b 81 e3 00 02 00 00 fa 31 ff 48 89 de e8 74 b7 85 f8 48 85 db RSP: 0018:ffffc90000d27d18 EFLAGS: 00000293 RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000000 RDX: ffff888010da0000 RSI: ffffffff88ebad17 RDI: 0000000000000000 RBP: ffff88814174c864 R08: 0000000000000001 R09: 0000000000000001 R10: ffffffff81772e05 R11: 0000000000000000 R12: 0000000000000001 R13: ffff88814174c800 R14: ffff88814174c864 R15: ffff888143385804 acpi_idle_enter+0x361/0x500 drivers/acpi/processor_idle.c:647 cpuidle_enter_state+0x1b1/0xc80 drivers/cpuidle/cpuidle.c:237 cpuidle_enter+0x4a/0xa0 drivers/cpuidle/cpuidle.c:351 call_cpuidle kernel/sched/idle.c:158 [inline] cpuidle_idle_call kernel/sched/idle.c:239 [inline] do_idle+0x3e1/0x590 kernel/sched/idle.c:299 cpu_startup_entry+0x14/0x20 kernel/sched/idle.c:396 start_secondary+0x274/0x350 arch/x86/kernel/smpboot.c:271 secondary_startup_64_no_verify+0xb0/0xbb