============================================ WARNING: possible recursive locking detected syzkaller #0 Not tainted -------------------------------------------- syz.0.12764/10416 is trying to acquire lock: ffff8880509eb558 (&qdisc_xmit_lock_key#4){+.-.}-{3:3}, at: spin_lock include/linux/spinlock.h:351 [inline] ffff8880509eb558 (&qdisc_xmit_lock_key#4){+.-.}-{3:3}, at: __netif_tx_lock include/linux/netdevice.h:4685 [inline] ffff8880509eb558 (&qdisc_xmit_lock_key#4){+.-.}-{3:3}, at: sch_direct_xmit+0x3ba/0xcf0 net/sched/sch_generic.c:342 but task is already holding lock: ffff88807cdb6158 (&qdisc_xmit_lock_key#4){+.-.}-{3:3}, at: spin_lock include/linux/spinlock.h:351 [inline] ffff88807cdb6158 (&qdisc_xmit_lock_key#4){+.-.}-{3:3}, at: __netif_tx_lock include/linux/netdevice.h:4685 [inline] ffff88807cdb6158 (&qdisc_xmit_lock_key#4){+.-.}-{3:3}, at: __dev_queue_xmit+0x1d9d/0x4490 net/core/dev.c:4759 other info that might help us debug this: Possible unsafe locking scenario: CPU0 ---- lock(&qdisc_xmit_lock_key#4); lock(&qdisc_xmit_lock_key#4); *** DEADLOCK *** May be due to missing lock nesting notation 7 locks held by syz.0.12764/10416: #0: ffffffff8e3c4700 (rcu_read_lock_bh){....}-{1:3}, at: local_bh_disable include/linux/bottom_half.h:20 [inline] #0: ffffffff8e3c4700 (rcu_read_lock_bh){....}-{1:3}, at: rcu_read_lock_bh include/linux/rcupdate.h:918 [inline] #0: ffffffff8e3c4700 (rcu_read_lock_bh){....}-{1:3}, at: __dev_queue_xmit+0x276/0x4490 net/core/dev.c:4688 #1: ffff88807cdb6158 (&qdisc_xmit_lock_key#4){+.-.}-{3:3}, at: spin_lock include/linux/spinlock.h:351 [inline] #1: ffff88807cdb6158 (&qdisc_xmit_lock_key#4){+.-.}-{3:3}, at: __netif_tx_lock include/linux/netdevice.h:4685 [inline] #1: ffff88807cdb6158 (&qdisc_xmit_lock_key#4){+.-.}-{3:3}, at: __dev_queue_xmit+0x1d9d/0x4490 net/core/dev.c:4759 #2: ffffffff8e3c4760 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:331 [inline] #2: ffffffff8e3c4760 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:867 [inline] #2: ffffffff8e3c4760 (rcu_read_lock){....}-{1:3}, at: ip_output+0x60/0xa90 net/ipv4/ip_output.c:433 #3: ffffffff8e3c4760 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:331 [inline] #3: ffffffff8e3c4760 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:867 [inline] #3: ffffffff8e3c4760 (rcu_read_lock){....}-{1:3}, at: ip_finish_output2+0x356/0x21a0 net/ipv4/ip_output.c:230 #4: ffffffff8e3c4760 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:331 [inline] #4: ffffffff8e3c4760 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:867 [inline] #4: ffffffff8e3c4760 (rcu_read_lock){....}-{1:3}, at: arp_xmit+0x26/0x2e0 net/ipv4/arp.c:662 #5: ffffffff8e3c4700 (rcu_read_lock_bh){....}-{1:3}, at: local_bh_disable include/linux/bottom_half.h:20 [inline] #5: ffffffff8e3c4700 (rcu_read_lock_bh){....}-{1:3}, at: rcu_read_lock_bh include/linux/rcupdate.h:918 [inline] #5: ffffffff8e3c4700 (rcu_read_lock_bh){....}-{1:3}, at: __dev_queue_xmit+0x276/0x4490 net/core/dev.c:4688 #6: ffff888027b2a258 (dev->qdisc_tx_busylock ?: &qdisc_tx_busylock#3){+...}-{3:3}, at: spin_trylock include/linux/spinlock.h:361 [inline] #6: ffff888027b2a258 (dev->qdisc_tx_busylock ?: &qdisc_tx_busylock#3){+...}-{3:3}, at: qdisc_run_begin include/net/sch_generic.h:197 [inline] #6: ffff888027b2a258 (dev->qdisc_tx_busylock ?: &qdisc_tx_busylock#3){+...}-{3:3}, at: qdisc_run_begin include/net/sch_generic.h:194 [inline] #6: ffff888027b2a258 (dev->qdisc_tx_busylock ?: &qdisc_tx_busylock#3){+...}-{3:3}, at: __dev_xmit_skb net/core/dev.c:4139 [inline] #6: ffff888027b2a258 (dev->qdisc_tx_busylock ?: &qdisc_tx_busylock#3){+...}-{3:3}, at: __dev_queue_xmit+0x122b/0x4490 net/core/dev.c:4729 stack backtrace: CPU: 1 UID: 0 PID: 10416 Comm: syz.0.12764 Not tainted syzkaller #0 PREEMPT(full) Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/02/2025 Call Trace: __dump_stack lib/dump_stack.c:94 [inline] dump_stack_lvl+0x116/0x1f0 lib/dump_stack.c:120 print_deadlock_bug+0x1e9/0x240 kernel/locking/lockdep.c:3041 check_deadlock kernel/locking/lockdep.c:3093 [inline] validate_chain kernel/locking/lockdep.c:3895 [inline] __lock_acquire+0x1106/0x1c90 kernel/locking/lockdep.c:5237 lock_acquire kernel/locking/lockdep.c:5868 [inline] lock_acquire+0x179/0x350 kernel/locking/lockdep.c:5825 __raw_spin_lock include/linux/spinlock_api_smp.h:133 [inline] _raw_spin_lock+0x2e/0x40 kernel/locking/spinlock.c:154 spin_lock include/linux/spinlock.h:351 [inline] __netif_tx_lock include/linux/netdevice.h:4685 [inline] sch_direct_xmit+0x3ba/0xcf0 net/sched/sch_generic.c:342 __dev_xmit_skb net/core/dev.c:4152 [inline] __dev_queue_xmit+0x144d/0x4490 net/core/dev.c:4729 dev_queue_xmit include/linux/netdevice.h:3365 [inline] arp_xmit_finish net/ipv4/arp.c:654 [inline] NF_HOOK include/linux/netfilter.h:318 [inline] NF_HOOK include/linux/netfilter.h:312 [inline] arp_xmit+0x106/0x2e0 net/ipv4/arp.c:664 arp_send_dst net/ipv4/arp.c:320 [inline] arp_send_dst+0x1f9/0x270 net/ipv4/arp.c:301 arp_solicit+0x657/0x10a0 net/ipv4/arp.c:392 neigh_probe+0xce/0x110 net/core/neighbour.c:1098 __neigh_event_send+0xac5/0x13c0 net/core/neighbour.c:1271 neigh_event_send_probe include/net/neighbour.h:471 [inline] neigh_event_send include/net/neighbour.h:477 [inline] neigh_event_send include/net/neighbour.h:475 [inline] neigh_resolve_output+0x56b/0x940 net/core/neighbour.c:1579 neigh_output include/net/neighbour.h:547 [inline] ip_finish_output2+0x7f8/0x21a0 net/ipv4/ip_output.c:237 __ip_finish_output.part.0+0x1b4/0x350 net/ipv4/ip_output.c:315 __ip_finish_output net/ipv4/ip_output.c:303 [inline] ip_finish_output net/ipv4/ip_output.c:325 [inline] NF_HOOK_COND include/linux/netfilter.h:307 [inline] ip_output+0x35f/0xa90 net/ipv4/ip_output.c:438 dst_output include/net/dst.h:464 [inline] ip_local_out+0x38d/0x4d0 net/ipv4/ip_output.c:131 iptunnel_xmit+0x67a/0xad0 net/ipv4/ip_tunnel_core.c:84 ip_tunnel_xmit+0x1fd2/0x3850 net/ipv4/ip_tunnel.c:845 __gre_xmit+0x8bb/0xc00 net/ipv4/ip_gre.c:488 ipgre_xmit+0x523/0xb10 net/ipv4/ip_gre.c:692 __netdev_start_xmit include/linux/netdevice.h:5248 [inline] netdev_start_xmit include/linux/netdevice.h:5257 [inline] xmit_one net/core/dev.c:3845 [inline] dev_hard_start_xmit+0x97/0x740 net/core/dev.c:3861 __dev_queue_xmit+0xa46/0x4490 net/core/dev.c:4763 dev_queue_xmit include/linux/netdevice.h:3365 [inline] packet_xmit+0x23e/0x360 net/packet/af_packet.c:275 packet_snd net/packet/af_packet.c:3076 [inline] packet_sendmsg+0x2756/0x5850 net/packet/af_packet.c:3108 sock_sendmsg_nosec net/socket.c:727 [inline] __sock_sendmsg net/socket.c:742 [inline] __sys_sendto+0x4a3/0x520 net/socket.c:2244 __do_sys_sendto net/socket.c:2251 [inline] __se_sys_sendto net/socket.c:2247 [inline] __x64_sys_sendto+0xe0/0x1c0 net/socket.c:2247 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline] do_syscall_64+0xcd/0xfa0 arch/x86/entry/syscall_64.c:94 entry_SYSCALL_64_after_hwframe+0x77/0x7f RIP: 0033:0x7f6350f8f6c9 Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 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 73 01 c3 48 c7 c1 a8 ff ff ff f7 d8 64 89 01 48 RSP: 002b:00007f6351e26038 EFLAGS: 00000246 ORIG_RAX: 000000000000002c RAX: ffffffffffffffda RBX: 00007f63511e5fa0 RCX: 00007f6350f8f6c9 RDX: 00000000000000c7 RSI: 0000200000000240 RDI: 0000000000000003 RBP: 00007f6351011f91 R08: 0000200000000540 R09: 0000000000000014 R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000 R13: 00007f63511e6038 R14: 00007f63511e5fa0 R15: 00007ffc566d6ec8