rcu: INFO: rcu_preempt detected stalls on CPUs/tasks: rcu: 1-...!: (1 GPs behind) idle=106/1/0x4000000000000000 softirq=32272/32274 fqs=38 (detected by 0, t=10502 jiffies, g=48997, q=1267) ============================================ WARNING: possible recursive locking detected 5.10.0-rc4-next-20201123-syzkaller #0 Not tainted -------------------------------------------- syz-executor.2/16703 is trying to acquire lock: ffffffff8b342018 (rcu_node_0){-.-.}-{2:2}, at: rcu_dump_cpu_stacks+0xaf/0x295 kernel/rcu/tree_stall.h:337 but task is already holding lock: ffffffff8b342018 (rcu_node_0){-.-.}-{2:2}, at: print_other_cpu_stall kernel/rcu/tree_stall.h:546 [inline] ffffffff8b342018 (rcu_node_0){-.-.}-{2:2}, at: check_cpu_stall kernel/rcu/tree_stall.h:711 [inline] ffffffff8b342018 (rcu_node_0){-.-.}-{2:2}, at: rcu_pending kernel/rcu/tree.c:3770 [inline] ffffffff8b342018 (rcu_node_0){-.-.}-{2:2}, at: rcu_sched_clock_irq.cold+0x2b6/0x11be kernel/rcu/tree.c:2595 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.2/16703: #0: ffff888012c00158 (&mm->mmap_lock#2){++++}-{3:3}, at: mmap_read_trylock include/linux/mmap_lock.h:56 [inline] #0: ffff888012c00158 (&mm->mmap_lock#2){++++}-{3:3}, at: do_user_addr_fault+0x25c/0xba0 arch/x86/mm/fault.c:1339 #1: ffff8880163454f8 (ptlock_ptr(page)#2){+.+.}-{2:2}, at: spin_lock include/linux/spinlock.h:354 [inline] #1: ffff8880163454f8 (ptlock_ptr(page)#2){+.+.}-{2:2}, at: wp_page_copy+0x61d/0x23b0 mm/memory.c:2880 #2: ffffffff8b342018 (rcu_node_0){-.-.}-{2:2}, at: print_other_cpu_stall kernel/rcu/tree_stall.h:546 [inline] #2: ffffffff8b342018 (rcu_node_0){-.-.}-{2:2}, at: check_cpu_stall kernel/rcu/tree_stall.h:711 [inline] #2: ffffffff8b342018 (rcu_node_0){-.-.}-{2:2}, at: rcu_pending kernel/rcu/tree.c:3770 [inline] #2: ffffffff8b342018 (rcu_node_0){-.-.}-{2:2}, at: rcu_sched_clock_irq.cold+0x2b6/0x11be kernel/rcu/tree.c:2595 stack backtrace: CPU: 0 PID: 16703 Comm: syz-executor.2 Not tainted 5.10.0-rc4-next-20201123-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+0xaf/0x295 kernel/rcu/tree_stall.h:337 print_other_cpu_stall kernel/rcu/tree_stall.h:564 [inline] check_cpu_stall kernel/rcu/tree_stall.h:711 [inline] rcu_pending kernel/rcu/tree.c:3770 [inline] rcu_sched_clock_irq.cold+0x7c0/0x11be kernel/rcu/tree.c:2595 update_process_times+0x16d/0x200 kernel/time/timer.c:1782 tick_sched_handle+0x9b/0x180 kernel/time/tick-sched.c:206 tick_sched_timer+0x1b0/0x2d0 kernel/time/tick-sched.c:1358 __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 32 41 0b 00 f3 90 <44> 8b 64 24 48 31 ff 41 83 e4 01 44 89 e6 e8 6d 39 0b 00 45 85 e4 RSP: 0000:ffffc9000241f9a0 EFLAGS: 00000293 RAX: 0000000000000000 RBX: 1ffff92000483f38 RCX: ffffffff81654a03 RDX: ffff888069421ac0 RSI: ffffffff816549ee RDI: 0000000000000005 RBP: ffffc9000241fa80 R08: 0000000000000001 R09: ffff8880b9f36007 R10: 0000000000000000 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:823 [inline] flush_tlb_mm_range+0x2ac/0x3d0 arch/x86/mm/tlb.c:910 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:2901 do_wp_page+0x3fe/0x1930 mm/memory.c:3145 handle_pte_fault mm/memory.c:4403 [inline] __handle_mm_fault mm/memory.c:4520 [inline] handle_mm_fault+0x2f98/0x55d0 mm/memory.c:4618 do_user_addr_fault+0x55d/0xba0 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: 0033:0x410b26 Code: 88 48 20 48 8b 4c 24 50 80 60 20 01 48 89 48 10 48 8b 4c 24 60 48 89 48 18 8b 4c 24 5c 89 48 24 31 c0 48 8b 8c 04 20 01 00 00 <48> 89 8c 02 50 bf 18 01 48 83 c0 08 48 83 f8 48 75 e6 e8 f3 36 ff RSP: 002b:00007ffc911e7df0 EFLAGS: 00010287 RAX: 0000000000000008 RBX: 0000000000000064 RCX: 0000000000000000 RDX: 00000000000000a8 RSI: 00007f01aaecadb0 RDI: 000000000118bfd0 RBP: 000000000118bfc8 R08: 0000000000000000 R09: 00007f01aaecb700 R10: 00007f01aaecb9d0 R11: 0000000000000202 R12: 0000000000000dff R13: 0000000000000001 R14: 0000000000000002 R15: 000000000118bfd4