============================================ WARNING: possible recursive locking detected syzkaller #0 Not tainted -------------------------------------------- syz.2.4906/20154 is trying to acquire lock: ffff8880213ea318 (dev->qdisc_tx_busylock ?: &qdisc_tx_busylock#8){+...}-{3:3}, at: spin_lock include/linux/spinlock_rt.h:44 [inline] ffff8880213ea318 (dev->qdisc_tx_busylock ?: &qdisc_tx_busylock#8){+...}-{3:3}, at: __dev_xmit_skb net/core/dev.c:4148 [inline] ffff8880213ea318 (dev->qdisc_tx_busylock ?: &qdisc_tx_busylock#8){+...}-{3:3}, at: __dev_queue_xmit+0xd58/0x3b70 net/core/dev.c:4691 but task is already holding lock: ffff8880213ea318 (dev->qdisc_tx_busylock ?: &qdisc_tx_busylock#8){+...}-{3:3}, at: spin_lock include/linux/spinlock_rt.h:44 [inline] ffff8880213ea318 (dev->qdisc_tx_busylock ?: &qdisc_tx_busylock#8){+...}-{3:3}, at: __dev_xmit_skb net/core/dev.c:4148 [inline] ffff8880213ea318 (dev->qdisc_tx_busylock ?: &qdisc_tx_busylock#8){+...}-{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#8); lock(dev->qdisc_tx_busylock ?: &qdisc_tx_busylock#8); *** DEADLOCK *** May be due to missing lock nesting notation 18 locks held by syz.2.4906/20154: #0: ffff88814dd86ad0 (sk_lock-AF_INET6){+.+.}-{0:0}, at: lock_sock include/net/sock.h:1669 [inline] #0: ffff88814dd86ad0 (sk_lock-AF_INET6){+.+.}-{0:0}, at: sctp_sendmsg+0xb86/0x2590 net/sctp/socket.c:1971 #1: ffffffff8d9a8d80 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:331 [inline] #1: ffffffff8d9a8d80 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:841 [inline] #1: ffffffff8d9a8d80 (rcu_read_lock){....}-{1:3}, at: sctp_v6_xmit+0x60f/0x1300 net/sctp/ipv6.c:247 #2: ffffffff8d9a8d80 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:331 [inline] #2: ffffffff8d9a8d80 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:841 [inline] #2: ffffffff8d9a8d80 (rcu_read_lock){....}-{1:3}, at: ip6_finish_output2+0x710/0x1720 net/ipv6/ip6_output.c:126 #3: ffffffff8d84a960 (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: ffffffff8d9a8d80 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:331 [inline] #5: ffffffff8d9a8d80 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:841 [inline] #5: ffffffff8d9a8d80 (rcu_read_lock){....}-{1:3}, at: __rt_spin_lock kernel/locking/spinlock_rt.c:50 [inline] #5: ffffffff8d9a8d80 (rcu_read_lock){....}-{1:3}, at: rt_spin_lock+0x1bb/0x2c0 kernel/locking/spinlock_rt.c:57 #6: ffffffff8d9a8d80 (rcu_read_lock){....}-{1:3}, at: __local_bh_disable_ip+0xa1/0x400 kernel/softirq.c:163 #7: ffffffff8d9a8de0 (rcu_read_lock_bh){....}-{1:3}, at: local_bh_disable include/linux/bottom_half.h:20 [inline] #7: ffffffff8d9a8de0 (rcu_read_lock_bh){....}-{1:3}, at: rcu_read_lock_bh include/linux/rcupdate.h:892 [inline] #7: ffffffff8d9a8de0 (rcu_read_lock_bh){....}-{1:3}, at: __dev_queue_xmit+0x26f/0x3b70 net/core/dev.c:4650 #8: ffff8880213ea318 (dev->qdisc_tx_busylock ?: &qdisc_tx_busylock#8){+...}-{3:3}, at: spin_lock include/linux/spinlock_rt.h:44 [inline] #8: ffff8880213ea318 (dev->qdisc_tx_busylock ?: &qdisc_tx_busylock#8){+...}-{3:3}, at: __dev_xmit_skb net/core/dev.c:4148 [inline] #8: ffff8880213ea318 (dev->qdisc_tx_busylock ?: &qdisc_tx_busylock#8){+...}-{3:3}, at: __dev_queue_xmit+0xd58/0x3b70 net/core/dev.c:4691 #9: ffffffff8d9a8d80 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:331 [inline] #9: ffffffff8d9a8d80 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:841 [inline] #9: ffffffff8d9a8d80 (rcu_read_lock){....}-{1:3}, at: __rt_spin_lock kernel/locking/spinlock_rt.c:50 [inline] #9: ffffffff8d9a8d80 (rcu_read_lock){....}-{1:3}, at: rt_spin_lock+0x1bb/0x2c0 kernel/locking/spinlock_rt.c:57 #10: ffffffff8d9a8d80 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:331 [inline] #10: ffffffff8d9a8d80 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:841 [inline] #10: ffffffff8d9a8d80 (rcu_read_lock){....}-{1:3}, at: icmp6_send+0x1e9/0x1940 net/ipv6/icmp.c:479 #11: ffffffff8d84a960 (local_bh){.+.+}-{1:3}, at: __local_bh_disable_ip+0xa1/0x400 kernel/softirq.c:163 #12: ffff88802fa90c50 (k-slock-AF_INET6){+...}-{3:3}, at: icmpv6_xmit_lock net/ipv6/icmp.c:108 [inline] #12: ffff88802fa90c50 (k-slock-AF_INET6){+...}-{3:3}, at: icmp6_send+0xc5c/0x1940 net/ipv6/icmp.c:556 #13: ffffffff8d9a8d80 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:331 [inline] #13: ffffffff8d9a8d80 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:841 [inline] #13: ffffffff8d9a8d80 (rcu_read_lock){....}-{1:3}, at: __rt_spin_trylock kernel/locking/spinlock_rt.c:110 [inline] #13: ffffffff8d9a8d80 (rcu_read_lock){....}-{1:3}, at: rt_spin_trylock+0xfa/0x180 kernel/locking/spinlock_rt.c:118 #14: ffffffff8d9a8d80 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:331 [inline] #14: ffffffff8d9a8d80 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:841 [inline] #14: ffffffff8d9a8d80 (rcu_read_lock){....}-{1:3}, at: ip6_send_skb+0x10f/0x390 net/ipv6/ip6_output.c:1983 #15: ffffffff8d9a8d80 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:331 [inline] #15: ffffffff8d9a8d80 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:841 [inline] #15: ffffffff8d9a8d80 (rcu_read_lock){....}-{1:3}, at: ip6_finish_output2+0x710/0x1720 net/ipv6/ip6_output.c:126 #16: ffffffff8d84a960 (local_bh){.+.+}-{1:3}, at: __local_bh_disable_ip+0xa1/0x400 kernel/softirq.c:163 #17: ffffffff8d9a8de0 (rcu_read_lock_bh){....}-{1:3}, at: local_bh_disable include/linux/bottom_half.h:20 [inline] #17: ffffffff8d9a8de0 (rcu_read_lock_bh){....}-{1:3}, at: rcu_read_lock_bh include/linux/rcupdate.h:892 [inline] #17: ffffffff8d9a8de0 (rcu_read_lock_bh){....}-{1:3}, at: __dev_queue_xmit+0x26f/0x3b70 net/core/dev.c:4650 stack backtrace: CPU: 1 UID: 0 PID: 20154 Comm: syz.2.4906 Not tainted syzkaller #0 PREEMPT_{RT,(full)} Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/18/2025 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 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 dst_link_failure include/net/dst.h:429 [inline] ip6_tnl_xmit+0xe05/0x2b10 net/ipv6/ip6_tunnel.c:1285 ipxip6_tnl_xmit net/ipv6/ip6_tunnel.c:1401 [inline] ip6_tnl_start_xmit+0xc1d/0x1150 net/ipv6/ip6_tunnel.c:1449 __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+0x2ed/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_fragment+0x1407/0x1e60 net/ipv6/ip6_output.c:1031 NF_HOOK include/linux/netfilter.h:318 [inline] ip6_xmit+0x107a/0x1840 net/ipv6/ip6_output.c:367 sctp_v6_xmit+0xa33/0x1300 net/sctp/ipv6.c:248 sctp_packet_transmit+0x257e/0x2bb0 net/sctp/output.c:653 sctp_packet_singleton+0x233/0x330 net/sctp/outqueue.c:783 sctp_outq_flush_ctrl net/sctp/outqueue.c:914 [inline] sctp_outq_flush+0x4f0/0x3140 net/sctp/outqueue.c:1212 sctp_cmd_interpreter net/sctp/sm_sideeffect.c:-1 [inline] sctp_side_effects net/sctp/sm_sideeffect.c:1204 [inline] sctp_do_sm+0x5332/0x5a20 net/sctp/sm_sideeffect.c:1175 sctp_primitive_ASSOCIATE+0x95/0xc0 net/sctp/primitive.c:73 sctp_sendmsg_to_asoc+0x102d/0x1810 net/sctp/socket.c:1842 sctp_sendmsg+0x174f/0x2590 net/sctp/socket.c:2032 sock_sendmsg_nosec net/socket.c:714 [inline] __sock_sendmsg+0x19c/0x270 net/socket.c:729 __sys_sendto+0x3c7/0x520 net/socket.c:2228 __do_sys_sendto net/socket.c:2235 [inline] __se_sys_sendto net/socket.c:2231 [inline] __x64_sys_sendto+0xde/0x100 net/socket.c:2231 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: 0033:0x7fba1828eba9 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:00007fba164b4038 EFLAGS: 00000246 ORIG_RAX: 000000000000002c RAX: ffffffffffffffda RBX: 00007fba184d6180 RCX: 00007fba1828eba9 RDX: 0000000000000001 RSI: 0000200000000240 RDI: 0000000000000005 RBP: 00007fba18311e19 R08: 0000200000000080 R09: 000000000000001c R10: 0000000000000051 R11: 0000000000000246 R12: 0000000000000000 R13: 00007fba184d6218 R14: 00007fba184d6180 R15: 00007fffa6f04cc8