============================================ WARNING: possible recursive locking detected syzkaller #0 Not tainted -------------------------------------------- syz.0.5698/19166 is trying to acquire lock: ffff888026d44318 (dev->qdisc_tx_busylock ?: &qdisc_tx_busylock#3){+...}-{3:3}, at: spin_lock include/linux/spinlock_rt.h:44 [inline] ffff888026d44318 (dev->qdisc_tx_busylock ?: &qdisc_tx_busylock#3){+...}-{3:3}, at: __dev_xmit_skb net/core/dev.c:4148 [inline] ffff888026d44318 (dev->qdisc_tx_busylock ?: &qdisc_tx_busylock#3){+...}-{3:3}, at: __dev_queue_xmit+0xd58/0x3b70 net/core/dev.c:4691 but task is already holding lock: ffff888026d44318 (dev->qdisc_tx_busylock ?: &qdisc_tx_busylock#3){+...}-{3:3}, at: spin_lock include/linux/spinlock_rt.h:44 [inline] ffff888026d44318 (dev->qdisc_tx_busylock ?: &qdisc_tx_busylock#3){+...}-{3:3}, at: __dev_xmit_skb net/core/dev.c:4148 [inline] ffff888026d44318 (dev->qdisc_tx_busylock ?: &qdisc_tx_busylock#3){+...}-{3:3}, at: __dev_queue_xmit+0xd58/0x3b70 net/core/dev.c:4691 other info that might help us debug this: Possible unsafe locking scenario: CPU0 ---- lock(dev->qdisc_tx_busylock ?: &qdisc_tx_busylock#3); lock(dev->qdisc_tx_busylock ?: &qdisc_tx_busylock#3); *** DEADLOCK *** May be due to missing lock nesting notation 21 locks held by syz.0.5698/19166: #0: ffffffff8d9a8b80 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:331 [inline] #0: ffffffff8d9a8b80 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:841 [inline] #0: ffffffff8d9a8b80 (rcu_read_lock){....}-{1:3}, at: rawv6_send_hdrinc+0xc09/0x1790 net/ipv6/raw.c:659 #1: ffffffff8d9a8b80 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:331 [inline] #1: ffffffff8d9a8b80 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:841 [inline] #1: ffffffff8d9a8b80 (rcu_read_lock){....}-{1:3}, at: class_rcu_constructor include/linux/rcupdate.h:1155 [inline] #1: ffffffff8d9a8b80 (rcu_read_lock){....}-{1:3}, at: ip6_mr_output+0x1ca/0x1100 net/ipv6/ip6mr.c:2375 #2: ffffffff8d9a8b80 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:331 [inline] #2: ffffffff8d9a8b80 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:841 [inline] #2: ffffffff8d9a8b80 (rcu_read_lock){....}-{1:3}, at: ip6_finish_output2+0x710/0x1720 net/ipv6/ip6_output.c:126 #3: ffffffff8d84a760 (local_bh){.+.+}-{1:3}, at: __local_bh_disable_ip+0xa1/0x400 kernel/softirq.c:163 #4: ffff8880b8923d90 ((softirq_ctrl.lock)){+.+.}-{3:3}, at: spin_lock include/linux/spinlock_rt.h:44 [inline] #4: ffff8880b8923d90 ((softirq_ctrl.lock)){+.+.}-{3:3}, at: __local_bh_disable_ip+0x264/0x400 kernel/softirq.c:168 #5: ffffffff8d9a8b80 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:331 [inline] #5: ffffffff8d9a8b80 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:841 [inline] #5: ffffffff8d9a8b80 (rcu_read_lock){....}-{1:3}, at: __rt_spin_lock kernel/locking/spinlock_rt.c:50 [inline] #5: ffffffff8d9a8b80 (rcu_read_lock){....}-{1:3}, at: rt_spin_lock+0x1bb/0x2c0 kernel/locking/spinlock_rt.c:57 #6: ffffffff8d9a8b80 (rcu_read_lock){....}-{1:3}, at: __local_bh_disable_ip+0xa1/0x400 kernel/softirq.c:163 #7: ffffffff8d9a8be0 (rcu_read_lock_bh){....}-{1:3}, at: local_bh_disable include/linux/bottom_half.h:20 [inline] #7: ffffffff8d9a8be0 (rcu_read_lock_bh){....}-{1:3}, at: rcu_read_lock_bh include/linux/rcupdate.h:892 [inline] #7: ffffffff8d9a8be0 (rcu_read_lock_bh){....}-{1:3}, at: __dev_queue_xmit+0x26f/0x3b70 net/core/dev.c:4650 #8: ffff888026d44318 (dev->qdisc_tx_busylock ?: &qdisc_tx_busylock#3){+...}-{3:3}, at: spin_lock include/linux/spinlock_rt.h:44 [inline] #8: ffff888026d44318 (dev->qdisc_tx_busylock ?: &qdisc_tx_busylock#3){+...}-{3:3}, at: __dev_xmit_skb net/core/dev.c:4148 [inline] #8: ffff888026d44318 (dev->qdisc_tx_busylock ?: &qdisc_tx_busylock#3){+...}-{3:3}, at: __dev_queue_xmit+0xd58/0x3b70 net/core/dev.c:4691 #9: ffffffff8d9a8b80 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:331 [inline] #9: ffffffff8d9a8b80 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:841 [inline] #9: ffffffff8d9a8b80 (rcu_read_lock){....}-{1:3}, at: __rt_spin_lock kernel/locking/spinlock_rt.c:50 [inline] #9: ffffffff8d9a8b80 (rcu_read_lock){....}-{1:3}, at: rt_spin_lock+0x1bb/0x2c0 kernel/locking/spinlock_rt.c:57 #10: ffffffff8d9a8b80 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:331 [inline] #10: ffffffff8d9a8b80 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:841 [inline] #10: ffffffff8d9a8b80 (rcu_read_lock){....}-{1:3}, at: icmp6_send+0x1e9/0x1940 net/ipv6/icmp.c:479 #11: ffffffff8d84a760 (local_bh){.+.+}-{1:3}, at: __local_bh_disable_ip+0xa1/0x400 kernel/softirq.c:163 #12: ffff88814d268c50 (k-slock-AF_INET6){+...}-{3:3}, at: icmpv6_xmit_lock net/ipv6/icmp.c:108 [inline] #12: ffff88814d268c50 (k-slock-AF_INET6){+...}-{3:3}, at: icmp6_send+0xc5c/0x1940 net/ipv6/icmp.c:556 #13: ffffffff8d9a8b80 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:331 [inline] #13: ffffffff8d9a8b80 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:841 [inline] #13: ffffffff8d9a8b80 (rcu_read_lock){....}-{1:3}, at: __rt_spin_trylock kernel/locking/spinlock_rt.c:110 [inline] #13: ffffffff8d9a8b80 (rcu_read_lock){....}-{1:3}, at: rt_spin_trylock+0xfa/0x180 kernel/locking/spinlock_rt.c:118 #14: ffffffff8d9a8b80 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:331 [inline] #14: ffffffff8d9a8b80 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:841 [inline] #14: ffffffff8d9a8b80 (rcu_read_lock){....}-{1:3}, at: ip6_send_skb+0x10f/0x390 net/ipv6/ip6_output.c:1983 #15: ffffffff8d9a8b80 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:331 [inline] #15: ffffffff8d9a8b80 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:841 [inline] #15: ffffffff8d9a8b80 (rcu_read_lock){....}-{1:3}, at: ip6_finish_output2+0x710/0x1720 net/ipv6/ip6_output.c:126 #16: ffffffff8d84a760 (local_bh){.+.+}-{1:3}, at: __local_bh_disable_ip+0xa1/0x400 kernel/softirq.c:163 #17: ffffffff8d9a8b80 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:331 [inline] #17: ffffffff8d9a8b80 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:841 [inline] #17: ffffffff8d9a8b80 (rcu_read_lock){....}-{1:3}, at: ndisc_send_skb+0x20c/0x1440 net/ipv6/ndisc.c:482 #18: ffffffff8d9a8b80 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:331 [inline] #18: ffffffff8d9a8b80 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:841 [inline] #18: ffffffff8d9a8b80 (rcu_read_lock){....}-{1:3}, at: ip6_finish_output2+0x710/0x1720 net/ipv6/ip6_output.c:126 #19: ffffffff8d84a760 (local_bh){.+.+}-{1:3}, at: __local_bh_disable_ip+0xa1/0x400 kernel/softirq.c:163 #20: ffffffff8d9a8be0 (rcu_read_lock_bh){....}-{1:3}, at: local_bh_disable include/linux/bottom_half.h:20 [inline] #20: ffffffff8d9a8be0 (rcu_read_lock_bh){....}-{1:3}, at: rcu_read_lock_bh include/linux/rcupdate.h:892 [inline] #20: ffffffff8d9a8be0 (rcu_read_lock_bh){....}-{1:3}, at: __dev_queue_xmit+0x26f/0x3b70 net/core/dev.c:4650 stack backtrace: CPU: 1 UID: 0 PID: 19166 Comm: syz.0.5698 Not tainted syzkaller #0 PREEMPT_{RT,(full)} Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/12/2025 Call Trace: dump_stack_lvl+0x189/0x250 lib/dump_stack.c:120 print_deadlock_bug+0x28b/0x2a0 kernel/locking/lockdep.c:3041 check_deadlock kernel/locking/lockdep.c:3093 [inline] validate_chain+0x1a3f/0x2140 kernel/locking/lockdep.c:3895 __lock_acquire+0xab9/0xd20 kernel/locking/lockdep.c:5237 lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5868 rt_spin_lock+0x88/0x2c0 kernel/locking/spinlock_rt.c:56 spin_lock include/linux/spinlock_rt.h:44 [inline] __dev_xmit_skb net/core/dev.c:4148 [inline] __dev_queue_xmit+0xd58/0x3b70 net/core/dev.c:4691 neigh_output include/net/neighbour.h:547 [inline] ip6_finish_output2+0x1273/0x1720 net/ipv6/ip6_output.c:141 NF_HOOK include/linux/netfilter.h:318 [inline] ndisc_send_skb+0xb54/0x1440 net/ipv6/ndisc.c:512 ndisc_send_ns net/ipv6/ndisc.c:670 [inline] ndisc_solicit+0x444/0x610 net/ipv6/ndisc.c:-1 neigh_probe net/core/neighbour.c:1098 [inline] __neigh_event_send+0xf65/0x1580 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_resolve_output+0x19f/0x780 net/core/neighbour.c:1579 neigh_output include/net/neighbour.h:547 [inline] ip6_finish_output2+0x1273/0x1720 net/ipv6/ip6_output.c:141 ip6_send_skb+0x1d5/0x390 net/ipv6/ip6_output.c:1984 icmp6_send+0x12c6/0x1940 net/ipv6/icmp.c:634 __icmpv6_send include/linux/icmpv6.h:28 [inline] icmpv6_send include/linux/icmpv6.h:49 [inline] ip6_link_failure+0x3b/0x4c0 net/ipv6/route.c:2843 ip_tunnel_xmit+0x175e/0x2390 net/ipv4/ip_tunnel.c:865 __gre_xmit net/ipv4/ip_gre.c:488 [inline] gre_tap_xmit+0x590/0x7a0 net/ipv4/ip_gre.c:776 __netdev_start_xmit include/linux/netdevice.h:5222 [inline] netdev_start_xmit include/linux/netdevice.h:5231 [inline] xmit_one net/core/dev.c:3839 [inline] dev_hard_start_xmit+0x2f0/0x870 net/core/dev.c:3855 sch_direct_xmit+0x241/0x4b0 net/sched/sch_generic.c:344 __dev_xmit_skb net/core/dev.c:4164 [inline] __dev_queue_xmit+0x19fc/0x3b70 net/core/dev.c:4691 neigh_output include/net/neighbour.h:547 [inline] ip6_finish_output2+0x1273/0x1720 net/ipv6/ip6_output.c:141 ip6_mr_output+0x4e9/0x1100 net/ipv6/ip6mr.c:2415 NF_HOOK include/linux/netfilter.h:318 [inline] rawv6_send_hdrinc+0xda3/0x1790 net/ipv6/raw.c:661 rawv6_sendmsg+0x12e2/0x1820 net/ipv6/raw.c:906 sock_sendmsg_nosec net/socket.c:714 [inline] __sock_sendmsg+0x19c/0x270 net/socket.c:729 ____sys_sendmsg+0x508/0x820 net/socket.c:2614 ___sys_sendmsg+0x21f/0x2a0 net/socket.c:2668 __sys_sendmsg net/socket.c:2700 [inline] __do_sys_sendmsg net/socket.c:2705 [inline] __se_sys_sendmsg net/socket.c:2703 [inline] __x64_sys_sendmsg+0x1a1/0x260 net/socket.c:2703 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline] do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94 entry_SYSCALL_64_after_hwframe+0x77/0x7f RIP: 0033:0x7f73aafdebe9 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:00007f73a9246038 EFLAGS: 00000246 ORIG_RAX: 000000000000002e RAX: ffffffffffffffda RBX: 00007f73ab205fa0 RCX: 00007f73aafdebe9 RDX: 0000000000000000 RSI: 0000200000000000 RDI: 0000000000000005 RBP: 00007f73ab061e19 R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000 R13: 00007f73ab206038 R14: 00007f73ab205fa0 R15: 00007ffd3ee30c18