====================================================== WARNING: possible circular locking dependency detected syzkaller #0 Not tainted ------------------------------------------------------ pr/ttyS0/31 is trying to acquire lock: ffff88807a448558 (_xmit_X25#2){+.-.}-{3:3}, at: spin_lock include/linux/spinlock.h:347 [inline] ffff88807a448558 (_xmit_X25#2){+.-.}-{3:3}, at: __netif_tx_lock include/linux/netdevice.h:4865 [inline] ffff88807a448558 (_xmit_X25#2){+.-.}-{3:3}, at: __dev_queue_xmit+0xe9d/0x3920 net/core/dev.c:5060 but task is already holding lock: ffff8880217d35c0 (&lapb->lock){+.-.}-{3:3}, at: spin_lock_bh include/linux/spinlock.h:353 [inline] ffff8880217d35c0 (&lapb->lock){+.-.}-{3:3}, at: lapb_t1timer_expiry+0x33/0xaa0 net/lapb/lapb_timer.c:99 which lock already depends on the new lock. the existing dependency chain (in reverse order) is: -> #2 (&lapb->lock){+.-.}-{3:3}: __raw_spin_lock_bh include/linux/spinlock_api_smp.h:182 [inline] _raw_spin_lock_bh+0x36/0x50 kernel/locking/spinlock.c:205 spin_lock_bh include/linux/spinlock.h:353 [inline] lapb_data_received+0xfc/0x1c0 net/lapb/lapb_iface.c:398 lapbeth_rcv+0x34d/0x640 drivers/net/wan/lapbether.c:142 __netif_receive_skb_one_core net/core/dev.c:6405 [inline] __netif_receive_skb net/core/dev.c:6518 [inline] process_backlog+0xc26/0x18b0 net/core/dev.c:6869 __napi_poll+0xaa/0x330 net/core/dev.c:7938 napi_poll net/core/dev.c:8001 [inline] net_rx_action+0x61d/0xf50 net/core/dev.c:8158 handle_softirqs+0x265/0x8d0 kernel/softirq.c:669 do_softirq+0x77/0xd0 kernel/softirq.c:569 __local_bh_enable_ip+0x100/0x140 kernel/softirq.c:473 spin_unlock_bh include/linux/spinlock.h:407 [inline] lapb_device_event+0x4f3/0x680 net/lapb/lapb_iface.c:527 notifier_call_chain+0x1a5/0x3d0 kernel/notifier.c:86 call_netdevice_notifiers_extack net/core/dev.c:2351 [inline] call_netdevice_notifiers net/core/dev.c:2365 [inline] __dev_notify_flags+0x31e/0x510 net/core/dev.c:10004 netif_change_flags+0xde/0x1b0 net/core/dev.c:10033 dev_change_flags+0x128/0x260 net/core/dev_api.c:68 devinet_ioctl+0x966/0x1c50 net/ipv4/devinet.c:1189 inet_ioctl+0x42a/0x560 net/ipv4/af_inet.c:1007 sock_do_ioctl+0x101/0x320 net/socket.c:1328 sock_ioctl+0x57a/0x7e0 net/socket.c:1449 vfs_ioctl fs/ioctl.c:51 [inline] __do_sys_ioctl fs/ioctl.c:597 [inline] __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:583 do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline] do_syscall_64+0x166/0x520 arch/x86/entry/syscall_64.c:84 entry_SYSCALL_64_after_hwframe+0x77/0x7f -> #1 (&lapbeth->up_lock){+.-.}-{3:3}: __raw_spin_lock_bh include/linux/spinlock_api_smp.h:182 [inline] _raw_spin_lock_bh+0x36/0x50 kernel/locking/spinlock.c:205 spin_lock_bh include/linux/spinlock.h:353 [inline] lapbeth_xmit+0x32/0x260 drivers/net/wan/lapbether.c:191 __netdev_start_xmit include/linux/netdevice.h:5456 [inline] netdev_start_xmit include/linux/netdevice.h:5465 [inline] xmit_one net/core/dev.c:4057 [inline] dev_hard_start_xmit+0x2cd/0x830 net/core/dev.c:4073 __dev_queue_xmit+0x14d1/0x3920 net/core/dev.c:5066 dev_queue_xmit include/linux/netdevice.h:3483 [inline] tx+0x6b/0x190 drivers/block/aoe/aoenet.c:62 kthread+0x1ed/0x420 drivers/block/aoe/aoecmd.c:1241 kthread+0x38b/0x480 kernel/kthread.c:436 ret_from_fork+0x514/0xb70 arch/x86/kernel/process.c:158 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245 -> #0 (_xmit_X25#2){+.-.}-{3:3}: check_prev_add kernel/locking/lockdep.c:3209 [inline] check_prevs_add kernel/locking/lockdep.c:3328 [inline] validate_chain kernel/locking/lockdep.c:3952 [inline] __lock_acquire+0x164c/0x2de0 kernel/locking/lockdep.c:5288 lock_acquire+0x115/0x350 kernel/locking/lockdep.c:5942 __raw_spin_lock include/linux/spinlock_api_smp.h:190 [inline] _raw_spin_lock+0x2e/0x40 kernel/locking/spinlock.c:173 spin_lock include/linux/spinlock.h:347 [inline] __netif_tx_lock include/linux/netdevice.h:4865 [inline] __dev_queue_xmit+0xe9d/0x3920 net/core/dev.c:5060 neigh_output include/net/neighbour.h:554 [inline] ip_finish_output2+0xc4b/0x10b0 net/ipv4/ip_output.c:236 NF_HOOK_COND include/linux/netfilter.h:314 [inline] ip_output+0x29f/0x450 net/ipv4/ip_output.c:437 iptunnel_xmit+0x626/0xd10 net/ipv4/ip_tunnel_core.c:97 udp_tunnel_xmit_skb+0x29b/0x3e0 net/ipv4/udp_tunnel_core.c:187 vxlan_xmit_one+0x20d2/0x2f80 drivers/net/vxlan/vxlan_core.c:2607 vxlan_xmit+0x2afc/0x45c0 drivers/net/vxlan/vxlan_core.c:2917 __netdev_start_xmit include/linux/netdevice.h:5456 [inline] netdev_start_xmit include/linux/netdevice.h:5465 [inline] xmit_one net/core/dev.c:4057 [inline] dev_hard_start_xmit+0x2cd/0x830 net/core/dev.c:4073 __dev_queue_xmit+0x14d1/0x3920 net/core/dev.c:5066 lapb_data_transmit+0x90/0xb0 net/lapb/lapb_iface.c:447 lapb_transmit_buffer+0x163/0x200 net/lapb/lapb_out.c:149 lapb_t1timer_expiry+0x68d/0xaa0 net/lapb/lapb_timer.c:-1 call_timer_fn+0x18d/0x5f0 kernel/time/timer.c:1749 expire_timers kernel/time/timer.c:1800 [inline] __run_timers kernel/time/timer.c:2375 [inline] __run_timer_base+0x652/0x8b0 kernel/time/timer.c:2387 run_timer_base kernel/time/timer.c:2396 [inline] run_timer_softirq+0xb7/0x170 kernel/time/timer.c:2406 handle_softirqs+0x265/0x8d0 kernel/softirq.c:669 __do_softirq kernel/softirq.c:703 [inline] invoke_softirq kernel/softirq.c:542 [inline] __irq_exit_rcu+0xc6/0x220 kernel/softirq.c:786 irq_exit_rcu+0x9/0x30 kernel/softirq.c:809 instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1062 [inline] sysvec_apic_timer_interrupt+0xa6/0xc0 arch/x86/kernel/apic/apic.c:1062 asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:674 __raw_spin_unlock_irqrestore include/linux/spinlock_api_smp.h:211 [inline] _raw_spin_unlock_irqrestore+0x47/0x80 kernel/locking/spinlock.c:221 nbcon_emit_one kernel/printk/nbcon.c:1165 [inline] nbcon_kthread_func+0x724/0x8d0 kernel/printk/nbcon.c:1271 kthread+0x38b/0x480 kernel/kthread.c:436 ret_from_fork+0x514/0xb70 arch/x86/kernel/process.c:158 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245 other info that might help us debug this: Chain exists of: _xmit_X25#2 --> &lapbeth->up_lock --> &lapb->lock Possible unsafe locking scenario: CPU0 CPU1 ---- ---- lock(&lapb->lock); lock(&lapbeth->up_lock); lock(&lapb->lock); lock(_xmit_X25#2); *** DEADLOCK *** locks held by pr/ttyS0/31: 9, last CPU#0: #0: ffffffff8fe33dd8 (console_srcu){....}-{0:0}, at: rcu_try_lock_acquire include/linux/rcupdate.h:314 [inline] #0: ffffffff8fe33dd8 (console_srcu){....}-{0:0}, at: srcu_read_lock_nmisafe include/linux/srcu.h:493 [inline] #0: ffffffff8fe33dd8 (console_srcu){....}-{0:0}, at: console_srcu_read_lock+0x30/0x60 kernel/printk/printk.c:291 #1: ffffc90000007ce0 ((&lapb->t1timer)){+.-.}-{0:0}, at: call_timer_fn+0xd5/0x5f0 kernel/time/timer.c:1746 #2: ffff8880217d35c0 (&lapb->lock){+.-.}-{3:3}, at: spin_lock_bh include/linux/spinlock.h:353 [inline] #2: ffff8880217d35c0 (&lapb->lock){+.-.}-{3:3}, at: lapb_t1timer_expiry+0x33/0xaa0 net/lapb/lapb_timer.c:99 #3: ffffffff8ff5a380 (rcu_read_lock_bh){....}-{1:3}, at: local_bh_disable include/linux/bottom_half.h:20 [inline] #3: ffffffff8ff5a380 (rcu_read_lock_bh){....}-{1:3}, at: rcu_read_lock_bh include/linux/rcupdate.h:902 [inline] #3: ffffffff8ff5a380 (rcu_read_lock_bh){....}-{1:3}, at: __dev_queue_xmit+0x29b/0x3920 net/core/dev.c:4980 #4: ffffffff8ff5a320 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:309 [inline] #4: ffffffff8ff5a320 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:849 [inline] #4: ffffffff8ff5a320 (rcu_read_lock){....}-{1:3}, at: vxlan_xmit+0xd8/0x45c0 drivers/net/vxlan/vxlan_core.c:2804 #5: ffffffff8ff5a320 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:309 [inline] #5: ffffffff8ff5a320 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:849 [inline] #5: ffffffff8ff5a320 (rcu_read_lock){....}-{1:3}, at: vxlan_xmit_one+0x149d/0x2f80 drivers/net/vxlan/vxlan_core.c:2522 #6: ffffffff8ff5a320 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:309 [inline] #6: ffffffff8ff5a320 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:849 [inline] #6: ffffffff8ff5a320 (rcu_read_lock){....}-{1:3}, at: ip_output+0x5a/0x450 net/ipv4/ip_output.c:432 #7: ffffffff8ff5a320 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:309 [inline] #7: ffffffff8ff5a320 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:849 [inline] #7: ffffffff8ff5a320 (rcu_read_lock){....}-{1:3}, at: ip_finish_output2+0x3de/0x10b0 net/ipv4/ip_output.c:229 #8: ffffffff8ff5a380 (rcu_read_lock_bh){....}-{1:3}, at: local_bh_disable include/linux/bottom_half.h:20 [inline] #8: ffffffff8ff5a380 (rcu_read_lock_bh){....}-{1:3}, at: rcu_read_lock_bh include/linux/rcupdate.h:902 [inline] #8: ffffffff8ff5a380 (rcu_read_lock_bh){....}-{1:3}, at: __dev_queue_xmit+0x29b/0x3920 net/core/dev.c:4980 stack backtrace: CPU: 0 UID: 0 PID: 31 Comm: pr/ttyS0 Not tainted syzkaller #0 PREEMPT(full) Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/07/2026 Call Trace: dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120 print_circular_bug+0x2e2/0x300 kernel/locking/lockdep.c:2087 check_noncircular+0x12f/0x150 kernel/locking/lockdep.c:2219 check_prev_add kernel/locking/lockdep.c:3209 [inline] check_prevs_add kernel/locking/lockdep.c:3328 [inline] validate_chain kernel/locking/lockdep.c:3952 [inline] __lock_acquire+0x164c/0x2de0 kernel/locking/lockdep.c:5288 lock_acquire+0x115/0x350 kernel/locking/lockdep.c:5942 __raw_spin_lock include/linux/spinlock_api_smp.h:190 [inline] _raw_spin_lock+0x2e/0x40 kernel/locking/spinlock.c:173 spin_lock include/linux/spinlock.h:347 [inline] __netif_tx_lock include/linux/netdevice.h:4865 [inline] __dev_queue_xmit+0xe9d/0x3920 net/core/dev.c:5060 neigh_output include/net/neighbour.h:554 [inline] ip_finish_output2+0xc4b/0x10b0 net/ipv4/ip_output.c:236 NF_HOOK_COND include/linux/netfilter.h:314 [inline] ip_output+0x29f/0x450 net/ipv4/ip_output.c:437 iptunnel_xmit+0x626/0xd10 net/ipv4/ip_tunnel_core.c:97 udp_tunnel_xmit_skb+0x29b/0x3e0 net/ipv4/udp_tunnel_core.c:187 vxlan_xmit_one+0x20d2/0x2f80 drivers/net/vxlan/vxlan_core.c:2607 vxlan_xmit+0x2afc/0x45c0 drivers/net/vxlan/vxlan_core.c:2917 __netdev_start_xmit include/linux/netdevice.h:5456 [inline] netdev_start_xmit include/linux/netdevice.h:5465 [inline] xmit_one net/core/dev.c:4057 [inline] dev_hard_start_xmit+0x2cd/0x830 net/core/dev.c:4073 __dev_queue_xmit+0x14d1/0x3920 net/core/dev.c:5066 lapb_data_transmit+0x90/0xb0 net/lapb/lapb_iface.c:447 lapb_transmit_buffer+0x163/0x200 net/lapb/lapb_out.c:149 lapb_t1timer_expiry+0x68d/0xaa0 net/lapb/lapb_timer.c:-1 call_timer_fn+0x18d/0x5f0 kernel/time/timer.c:1749 expire_timers kernel/time/timer.c:1800 [inline] __run_timers kernel/time/timer.c:2375 [inline] __run_timer_base+0x652/0x8b0 kernel/time/timer.c:2387 run_timer_base kernel/time/timer.c:2396 [inline] run_timer_softirq+0xb7/0x170 kernel/time/timer.c:2406 handle_softirqs+0x265/0x8d0 kernel/softirq.c:669 __do_softirq kernel/softirq.c:703 [inline] invoke_softirq kernel/softirq.c:542 [inline] __irq_exit_rcu+0xc6/0x220 kernel/softirq.c:786 irq_exit_rcu+0x9/0x30 kernel/softirq.c:809 instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1062 [inline] sysvec_apic_timer_interrupt+0xa6/0xc0 arch/x86/kernel/apic/apic.c:1062 asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:674 RIP: 0010:__raw_spin_unlock_irqrestore include/linux/spinlock_api_smp.h:211 [inline] RIP: 0010:_raw_spin_unlock_irqrestore+0x47/0x80 kernel/locking/spinlock.c:221 Code: f7 e8 cd dc 9f f5 f7 c3 00 02 00 00 74 05 e8 80 75 cc f5 9c 58 a9 00 02 00 00 75 29 f7 c3 00 02 00 00 74 01 fb bf 01 00 00 00 e4 d0 90 f5 65 48 8b 05 bc e1 ba 08 48 85 c0 74 18 5b 41 5e e9 RSP: 0000:ffffc90000a77ca8 EFLAGS: 00000206 RAX: 0000000000000006 RBX: 0000000000000206 RCX: 8000000000000001 RDX: 0000000000000000 RSI: ffffffff8e6a0e4d RDI: 0000000000000001 RBP: ffffc90000a77e18 R08: ffffffff919d5fbf R09: 1ffffffff233abf7 R10: dffffc0000000000 R11: fffffbfff233abf8 R12: 0000000000000002 R13: ffff88801f6b9f40 R14: ffffffff9bfeb6c0 R15: dffffc0000000000 nbcon_emit_one kernel/printk/nbcon.c:1165 [inline] nbcon_kthread_func+0x724/0x8d0 kernel/printk/nbcon.c:1271 kthread+0x38b/0x480 kernel/kthread.c:436 ret_from_fork+0x514/0xb70 arch/x86/kernel/process.c:158 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245 ---------------- Code disassembly (best guess): 0: f7 e8 imul %eax 2: cd dc int $0xdc 4: 9f lahf 5: f5 cmc 6: f7 c3 00 02 00 00 test $0x200,%ebx c: 74 05 je 0x13 e: e8 80 75 cc f5 call 0xf5cc7593 13: 9c pushf 14: 58 pop %rax 15: a9 00 02 00 00 test $0x200,%eax 1a: 75 29 jne 0x45 1c: f7 c3 00 02 00 00 test $0x200,%ebx 22: 74 01 je 0x25 24: fb sti 25: bf 01 00 00 00 mov $0x1,%edi * 2a: e8 e4 d0 90 f5 call 0xf590d113 <-- trapping instruction 2f: 65 48 8b 05 bc e1 ba mov %gs:0x8bae1bc(%rip),%rax # 0x8bae1f3 36: 08 37: 48 85 c0 test %rax,%rax 3a: 74 18 je 0x54 3c: 5b pop %rbx 3d: 41 5e pop %r14 3f: e9 .byte 0xe9