rcu: INFO: rcu_preempt detected stalls on CPUs/tasks: rcu: 0-...!: (0 ticks this GP) idle=07e/1/0x4000000000000000 softirq=18983/18983 fqs=0 (detected by 1, t=10502 jiffies, g=27201, q=193) ============================================ WARNING: possible recursive locking detected 5.10.0-next-20201223-syzkaller #0 Not tainted -------------------------------------------- syz-executor.5/12454 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 3 locks held by syz-executor.5/12454: #0: ffff88801141f958 (&mm->mmap_lock#2){++++}-{3:3}, at: mmap_read_trylock include/linux/mmap_lock.h:136 [inline] #0: ffff88801141f958 (&mm->mmap_lock#2){++++}-{3:3}, at: do_user_addr_fault+0x25f/0xc50 arch/x86/mm/fault.c:1339 #1: ffff88801b43feb8 (ptlock_ptr(page)#2){+.+.}-{2:2}, at: spin_lock include/linux/spinlock.h:354 [inline] #1: ffff88801b43feb8 (ptlock_ptr(page)#2){+.+.}-{2:2}, at: wp_page_copy+0x61d/0x23b0 mm/memory.c:2880 #2: ffffffff8b36b758 (rcu_node_0){-.-.}-{2:2}, at: print_other_cpu_stall kernel/rcu/tree_stall.h:493 [inline] #2: ffffffff8b36b758 (rcu_node_0){-.-.}-{2:2}, at: check_cpu_stall kernel/rcu/tree_stall.h:652 [inline] #2: ffffffff8b36b758 (rcu_node_0){-.-.}-{2:2}, at: rcu_pending kernel/rcu/tree.c:3751 [inline] #2: ffffffff8b36b758 (rcu_node_0){-.-.}-{2:2}, at: rcu_sched_clock_irq.cold+0xbc/0xec3 kernel/rcu/tree.c:2580 stack backtrace: CPU: 1 PID: 12454 Comm: syz-executor.5 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+0x1b0/0x4b0 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 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 RSP: 0000:ffffc90001d6f9a0 EFLAGS: 00000293 RAX: 0000000000000000 RBX: 1ffff920003adf38 RCX: 0000000000000000 RDX: ffff8880730e1c00 RSI: ffffffff8167363e RDI: 0000000000000003 RBP: ffffc90001d6fa80 R08: 0000000000000000 R09: 0000000000000000 R10: ffffffff81673653 R11: 0000000000000000 R12: 0000000000000001 R13: 0000000000000000 R14: 0000000000000001 R15: 0000000000000008 smp_call_function_many_cond+0x25f/0x9d0 kernel/smp.c:648 on_each_cpu_cond_mask+0x50/0x160 kernel/smp.c:899 __flush_tlb_others arch/x86/include/asm/paravirt.h:74 [inline] flush_tlb_others arch/x86/mm/tlb.c:829 [inline] flush_tlb_mm_range+0x2ac/0x3d0 arch/x86/mm/tlb.c:916 flush_tlb_page arch/x86/include/asm/tlbflush.h:235 [inline] ptep_clear_flush+0x12b/0x160 mm/pgtable-generic.c:97 wp_page_copy+0x8e8/0x23b0 mm/memory.c:2903 do_wp_page+0x3fe/0x1930 mm/memory.c:3147 handle_pte_fault mm/memory.c:4405 [inline] __handle_mm_fault mm/memory.c:4522 [inline] handle_mm_fault+0x28e5/0x5640 mm/memory.c:4620 do_user_addr_fault+0x570/0xc50 arch/x86/mm/fault.c:1398 handle_page_fault arch/x86/mm/fault.c:1455 [inline] exc_page_fault+0x9e/0x180 arch/x86/mm/fault.c:1511 asm_exc_page_fault+0x1e/0x30 arch/x86/include/asm/idtentry.h:580 RIP: 0033:0x412ee8 Code: 00 00 4c 89 ff 83 f3 01 89 54 24 0c e8 41 30 ff ff 38 c3 8b 54 24 0c 0f 86 5c 01 00 00 31 db e9 73 ff ff ff 66 0f 1f 44 00 00 <42> 89 14 85 00 00 77 00 e9 54 ff ff ff 0f 1f 00 89 eb 48 c1 e3 03 RSP: 002b:00007ffe3eb84cb0 EFLAGS: 00010246 RAX: 0000000041d104bd RBX: 0000000000000001 RCX: 0000001b2fd20000 RDX: 0000000041d104bd RSI: 0000000080000000 RDI: 0000000000000000 RBP: 000000000119c0b0 R08: 00000000000004bd R09: 0000000041d104c1 R10: 00007ffe3eb84e50 R11: 0000000000000000 R12: 00007fefd7708008 R13: 0000000000000000 R14: 00007fefd7708000 R15: ffffffff81784dd7