rcu: INFO: rcu_preempt detected stalls on CPUs/tasks: rcu: 0-...!: (1 GPs behind) idle=ae6/1/0x4000000000000000 softirq=53636/53638 fqs=23 (detected by 1, t=10502 jiffies, g=92905, q=374) ============================================ WARNING: possible recursive locking detected 5.9.0-rc7-next-20201001-syzkaller #0 Not tainted -------------------------------------------- syz-executor.0/26964 is trying to acquire lock: ffffffff8a55d118 (rcu_node_0){-.-.}-{2:2}, at: rcu_dump_cpu_stacks+0x9c/0x21e kernel/rcu/tree_stall.h:334 but task is already holding lock: ffffffff8a55d118 (rcu_node_0){-.-.}-{2:2}, at: print_other_cpu_stall kernel/rcu/tree_stall.h:493 [inline] ffffffff8a55d118 (rcu_node_0){-.-.}-{2:2}, at: check_cpu_stall kernel/rcu/tree_stall.h:652 [inline] ffffffff8a55d118 (rcu_node_0){-.-.}-{2:2}, at: rcu_pending kernel/rcu/tree.c:3700 [inline] ffffffff8a55d118 (rcu_node_0){-.-.}-{2:2}, at: rcu_sched_clock_irq.cold+0xbc/0xec3 kernel/rcu/tree.c:2572 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 syz-executor.0/26964: #0: ffffffff8a55d118 (rcu_node_0){-.-.}-{2:2}, at: print_other_cpu_stall kernel/rcu/tree_stall.h:493 [inline] #0: ffffffff8a55d118 (rcu_node_0){-.-.}-{2:2}, at: check_cpu_stall kernel/rcu/tree_stall.h:652 [inline] #0: ffffffff8a55d118 (rcu_node_0){-.-.}-{2:2}, at: rcu_pending kernel/rcu/tree.c:3700 [inline] #0: ffffffff8a55d118 (rcu_node_0){-.-.}-{2:2}, at: rcu_sched_clock_irq.cold+0xbc/0xec3 kernel/rcu/tree.c:2572 stack backtrace: CPU: 1 PID: 26964 Comm: syz-executor.0 Not tainted 5.9.0-rc7-next-20201001-syzkaller #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 Call Trace: __dump_stack lib/dump_stack.c:77 [inline] dump_stack+0x198/0x1fb lib/dump_stack.c:118 print_deadlock_bug kernel/locking/lockdep.c:2735 [inline] check_deadlock kernel/locking/lockdep.c:2776 [inline] validate_chain kernel/locking/lockdep.c:3567 [inline] __lock_acquire.cold+0x12e/0x3ad kernel/locking/lockdep.c:4817 lock_acquire+0x1f2/0xaa0 kernel/locking/lockdep.c:5419 __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline] _raw_spin_lock_irqsave+0x94/0xd0 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:3700 [inline] rcu_sched_clock_irq.cold+0x6db/0xec3 kernel/rcu/tree.c:2572 update_process_times+0x25/0xa0 kernel/time/timer.c:1712 tick_sched_handle+0x9b/0x180 kernel/time/tick-sched.c:176 tick_sched_timer+0x1d1/0x2a0 kernel/time/tick-sched.c:1328 __run_hrtimer kernel/time/hrtimer.c:1524 [inline] __hrtimer_run_queues+0x1ce/0xea0 kernel/time/hrtimer.c:1588 hrtimer_interrupt+0x334/0x940 kernel/time/hrtimer.c:1650 local_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1080 [inline] __sysvec_apic_timer_interrupt+0x146/0x540 arch/x86/kernel/apic/apic.c:1097 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+0xb2/0xf0 arch/x86/kernel/apic/apic.c:1091 asm_sysvec_apic_timer_interrupt+0x12/0x20 arch/x86/include/asm/idtentry.h:631 RIP: 0010:csd_lock_wait kernel/smp.c:227 [inline] RIP: 0010:smp_call_function_single+0x192/0x500 kernel/smp.c:512 Code: 10 8b 7c 24 1c 48 8d 74 24 40 48 89 44 24 50 48 8b 44 24 08 48 89 44 24 58 e8 2a fa ff ff 41 89 c5 eb 07 e8 a0 2b 0b 00 f3 90 <44> 8b 64 24 48 31 ff 41 83 e4 01 44 89 e6 e8 eb 27 0b 00 45 85 e4 RSP: 0018:ffffc90008f2fc00 EFLAGS: 00000246 RAX: 0000000000040000 RBX: 1ffff920011e5f84 RCX: ffffc90006109000 RDX: 0000000000040000 RSI: ffffffff816a1b60 RDI: 0000000000000005 RBP: ffffc90008f2fcc8 R08: 0000000000000001 R09: ffff8880ae437047 R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000001 R13: 0000000000000000 R14: 0000000000000001 R15: 0000000000000040 smp_call_function_many_cond+0x1a4/0xa10 kernel/smp.c:648 smp_call_function_many kernel/smp.c:711 [inline] smp_call_function kernel/smp.c:733 [inline] on_each_cpu+0x4c/0x1f0 kernel/smp.c:832 clock_was_set+0x18/0x20 kernel/time/hrtimer.c:876 do_settimeofday64 kernel/time/timekeeping.c:1331 [inline] do_settimeofday64+0x39d/0x570 kernel/time/timekeeping.c:1297 do_sys_settimeofday64 kernel/time/time.c:195 [inline] do_sys_settimeofday64+0x1de/0x260 kernel/time/time.c:169 __do_sys_clock_settime kernel/time/posix-timers.c:1079 [inline] __se_sys_clock_settime kernel/time/posix-timers.c:1067 [inline] __x64_sys_clock_settime+0x1a1/0x280 kernel/time/posix-timers.c:1067 do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46 entry_SYSCALL_64_after_hwframe+0x44/0xa9 RIP: 0033:0x45dd99 Code: 0d b4 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 db b3 fb ff c3 66 2e 0f 1f 84 00 00 00 00 RSP: 002b:00007f7294c00c78 EFLAGS: 00000246 ORIG_RAX: 00000000000000e3 RAX: ffffffffffffffda RBX: 0000000000001f80 RCX: 000000000045dd99 RDX: 0000000000000000 RSI: 0000000020000400 RDI: 0000000000000000 RBP: 000000000118bf58 R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000246 R12: 000000000118bf2c R13: 00007ffeb46d71ff R14: 00007f7294c019c0 R15: 000000000118bf2c