syzbot

============================================
WARNING: possible recursive locking detected
6.1.139-syzkaller #0 Not tainted
--------------------------------------------
syz.1.2145/9995 is trying to acquire lock:
ffff88801aa93a18 (dev->qdisc_tx_busylock ?: &qdisc_tx_busylock){+.-.}-{2:2}, at: spin_lock include/linux/spinlock.h:351 [inline]
ffff88801aa93a18 (dev->qdisc_tx_busylock ?: &qdisc_tx_busylock){+.-.}-{2:2}, at: __dev_xmit_skb net/core/dev.c:3925 [inline]
ffff88801aa93a18 (dev->qdisc_tx_busylock ?: &qdisc_tx_busylock){+.-.}-{2:2}, at: __dev_queue_xmit+0x208f/0x3760 net/core/dev.c:4300

but task is already holding lock:
ffff8880569f0258 (dev->qdisc_tx_busylock ?: &qdisc_tx_busylock){+.-.}-{2:2}, at: spin_trylock include/linux/spinlock.h:361 [inline]
ffff8880569f0258 (dev->qdisc_tx_busylock ?: &qdisc_tx_busylock){+.-.}-{2:2}, at: qdisc_run_begin include/net/sch_generic.h:195 [inline]
ffff8880569f0258 (dev->qdisc_tx_busylock ?: &qdisc_tx_busylock){+.-.}-{2:2}, at: __dev_xmit_skb net/core/dev.c:3882 [inline]
ffff8880569f0258 (dev->qdisc_tx_busylock ?: &qdisc_tx_busylock){+.-.}-{2:2}, at: __dev_queue_xmit+0x129a/0x3760 net/core/dev.c:4300

other info that might help us debug this:
 Possible unsafe locking scenario:

       CPU0
       ----
  lock(dev->qdisc_tx_busylock ?: &qdisc_tx_busylock);
  lock(dev->qdisc_tx_busylock ?: &qdisc_tx_busylock);

 *** DEADLOCK ***

 May be due to missing lock nesting notation

12 locks held by syz.1.2145/9995:
 #0: ffffc900001e0bc0 ((&ndev->rs_timer)){+.-.}-{0:0}, at: call_timer_fn+0xc1/0x670 kernel/time/timer.c:1501
 #1: ffffffff8c92ab20 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire include/linux/rcupdate.h:350 [inline]
 #1: ffffffff8c92ab20 (rcu_read_lock){....}-{1:2}, at: rcu_read_lock include/linux/rcupdate.h:791 [inline]
 #1: ffffffff8c92ab20 (rcu_read_lock){....}-{1:2}, at: ndisc_send_skb+0x1f2/0x1510 net/ipv6/ndisc.c:484
 #2: ffffffff8c92ab20 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire include/linux/rcupdate.h:350 [inline]
 #2: ffffffff8c92ab20 (rcu_read_lock){....}-{1:2}, at: rcu_read_lock include/linux/rcupdate.h:791 [inline]
 #2: ffffffff8c92ab20 (rcu_read_lock){....}-{1:2}, at: ip6_finish_output2+0x593/0x1590 net/ipv6/ip6_output.c:123
 #3: ffffffff8c92ab80 (rcu_read_lock_bh){....}-{1:2}, at: local_bh_disable include/linux/bottom_half.h:20 [inline]
 #3: ffffffff8c92ab80 (rcu_read_lock_bh){....}-{1:2}, at: rcu_read_lock_bh include/linux/rcupdate.h:843 [inline]
 #3: ffffffff8c92ab80 (rcu_read_lock_bh){....}-{1:2}, at: __dev_queue_xmit+0x26f/0x3760 net/core/dev.c:4257
 #4: ffff8880569f0258 (dev->qdisc_tx_busylock ?: &qdisc_tx_busylock){+.-.}-{2:2}, at: spin_trylock include/linux/spinlock.h:361 [inline]
 #4: ffff8880569f0258 (dev->qdisc_tx_busylock ?: &qdisc_tx_busylock){+.-.}-{2:2}, at: qdisc_run_begin include/net/sch_generic.h:195 [inline]
 #4: ffff8880569f0258 (dev->qdisc_tx_busylock ?: &qdisc_tx_busylock){+.-.}-{2:2}, at: __dev_xmit_skb net/core/dev.c:3882 [inline]
 #4: ffff8880569f0258 (dev->qdisc_tx_busylock ?: &qdisc_tx_busylock){+.-.}-{2:2}, at: __dev_queue_xmit+0x129a/0x3760 net/core/dev.c:4300
 #5: ffffffff8c92ab20 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire include/linux/rcupdate.h:350 [inline]
 #5: ffffffff8c92ab20 (rcu_read_lock){....}-{1:2}, at: rcu_read_lock include/linux/rcupdate.h:791 [inline]
 #5: ffffffff8c92ab20 (rcu_read_lock){....}-{1:2}, at: ip6_finish_output2+0x593/0x1590 net/ipv6/ip6_output.c:123
 #6: ffffffff8c92ab80 (rcu_read_lock_bh){....}-{1:2}, at: local_bh_disable include/linux/bottom_half.h:20 [inline]
 #6: ffffffff8c92ab80 (rcu_read_lock_bh){....}-{1:2}, at: rcu_read_lock_bh include/linux/rcupdate.h:843 [inline]
 #6: ffffffff8c92ab80 (rcu_read_lock_bh){....}-{1:2}, at: __dev_queue_xmit+0x26f/0x3760 net/core/dev.c:4257
 #7: ffff88802f9387f0 (k-slock-AF_INET6){+.-.}-{2:2}, at: spin_trylock include/linux/spinlock.h:361 [inline]
 #7: ffff88802f9387f0 (k-slock-AF_INET6){+.-.}-{2:2}, at: icmpv6_xmit_lock net/ipv6/icmp.c:108 [inline]
 #7: ffff88802f9387f0 (k-slock-AF_INET6){+.-.}-{2:2}, at: icmp6_send+0xb5f/0x18d0 net/ipv6/icmp.c:553
 #8: ffffffff8c92ab20 (rcu_read_lock){....}-{1:2}, at: local_bh_disable include/linux/bottom_half.h:20 [inline]
 #8: ffffffff8c92ab20 (rcu_read_lock){....}-{1:2}, at: icmp6_send+0xaa6/0x18d0 net/ipv6/icmp.c:544
 #9: ffffffff8c92ab20 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire include/linux/rcupdate.h:350 [inline]
 #9: ffffffff8c92ab20 (rcu_read_lock){....}-{1:2}, at: rcu_read_lock include/linux/rcupdate.h:791 [inline]
 #9: ffffffff8c92ab20 (rcu_read_lock){....}-{1:2}, at: ip6_send_skb+0x10b/0x380 net/ipv6/ip6_output.c:2007
 #10: ffffffff8c92ab20 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire include/linux/rcupdate.h:350 [inline]
 #10: ffffffff8c92ab20 (rcu_read_lock){....}-{1:2}, at: rcu_read_lock include/linux/rcupdate.h:791 [inline]
 #10: ffffffff8c92ab20 (rcu_read_lock){....}-{1:2}, at: ip6_finish_output2+0x593/0x1590 net/ipv6/ip6_output.c:123
 #11: ffffffff8c92ab80 (rcu_read_lock_bh){....}-{1:2}, at: local_bh_disable include/linux/bottom_half.h:20 [inline]
 #11: ffffffff8c92ab80 (rcu_read_lock_bh){....}-{1:2}, at: rcu_read_lock_bh include/linux/rcupdate.h:843 [inline]
 #11: ffffffff8c92ab80 (rcu_read_lock_bh){....}-{1:2}, at: __dev_queue_xmit+0x26f/0x3760 net/core/dev.c:4257

stack backtrace:
CPU: 1 PID: 9995 Comm: syz.1.2145 Not tainted 6.1.139-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/19/2025
Call Trace:
 <IRQ>
 dump_stack_lvl+0x168/0x22e lib/dump_stack.c:106
 __lock_acquire+0x122f/0x7c50 kernel/locking/lockdep.c:-1
 lock_acquire+0x1b4/0x490 kernel/locking/lockdep.c:5662
 __raw_spin_lock include/linux/spinlock_api_smp.h:133 [inline]
 _raw_spin_lock+0x2a/0x40 kernel/locking/spinlock.c:154
 spin_lock include/linux/spinlock.h:351 [inline]
 __dev_xmit_skb net/core/dev.c:3925 [inline]
 __dev_queue_xmit+0x208f/0x3760 net/core/dev.c:4300
 neigh_output include/net/neighbour.h:544 [inline]
 ip6_finish_output2+0xda2/0x1590 net/ipv6/ip6_output.c:138
 __ip6_finish_output net/ipv6/ip6_output.c:205 [inline]
 ip6_finish_output+0x5d3/0xa60 net/ipv6/ip6_output.c:216
 ip6_send_skb+0x1d1/0x380 net/ipv6/ip6_output.c:2008
 icmp6_send+0x1292/0x18d0 net/ipv6/icmp.c:632
 __icmpv6_send include/linux/icmpv6.h:28 [inline]
 icmpv6_send include/linux/icmpv6.h:49 [inline]
 ip6_link_failure+0x37/0x4c0 net/ipv6/route.c:2827
 dst_link_failure include/net/dst.h:423 [inline]
 ipip6_tunnel_xmit net/ipv6/sit.c:1039 [inline]
 sit_tunnel_xmit+0xaf0/0x1f60 net/ipv6/sit.c:1076
 __netdev_start_xmit include/linux/netdevice.h:4896 [inline]
 netdev_start_xmit include/linux/netdevice.h:4910 [inline]
 xmit_one net/core/dev.c:3658 [inline]
 dev_hard_start_xmit+0x262/0x870 net/core/dev.c:3674
 sch_direct_xmit+0x24e/0x4a0 net/sched/sch_generic.c:342
 qdisc_restart net/sched/sch_generic.c:407 [inline]
 __qdisc_run+0xadf/0x15f0 net/sched/sch_generic.c:415
 __dev_xmit_skb net/core/dev.c:3958 [inline]
 __dev_queue_xmit+0x107e/0x3760 net/core/dev.c:4300
 neigh_output include/net/neighbour.h:544 [inline]
 ip6_finish_output2+0xda2/0x1590 net/ipv6/ip6_output.c:138
 __ip6_finish_output net/ipv6/ip6_output.c:205 [inline]
 ip6_finish_output+0x5d3/0xa60 net/ipv6/ip6_output.c:216
 ip6tunnel_xmit+0x1a6/0x3a0 include/net/ip6_tunnel.h:161
 ip6_tnl_xmit+0x225b/0x2ab0 net/ipv6/ip6_tunnel.c:1280
 __gre6_xmit+0x960/0xc70 net/ipv6/ip6_gre.c:809
 ip6gre_xmit_ipv6 net/ipv6/ip6_gre.c:865 [inline]
 ip6gre_tunnel_xmit+0xf76/0x13d0 net/ipv6/ip6_gre.c:937
 __netdev_start_xmit include/linux/netdevice.h:4896 [inline]
 netdev_start_xmit include/linux/netdevice.h:4910 [inline]
 xmit_one net/core/dev.c:3658 [inline]
 dev_hard_start_xmit+0x262/0x870 net/core/dev.c:3674
 sch_direct_xmit+0x24e/0x4a0 net/sched/sch_generic.c:342
 __dev_xmit_skb net/core/dev.c:3895 [inline]
 __dev_queue_xmit+0x18cd/0x3760 net/core/dev.c:4300
 neigh_output include/net/neighbour.h:544 [inline]
 ip6_finish_output2+0xda2/0x1590 net/ipv6/ip6_output.c:138
 __ip6_finish_output net/ipv6/ip6_output.c:205 [inline]
 ip6_finish_output+0x5d3/0xa60 net/ipv6/ip6_output.c:216
 dst_output include/net/dst.h:453 [inline]
 NF_HOOK include/linux/netfilter.h:302 [inline]
 ndisc_send_skb+0xbfb/0x1510 net/ipv6/ndisc.c:513
 addrconf_rs_timer+0x2b8/0x600 net/ipv6/addrconf.c:3985
 call_timer_fn+0x1a0/0x670 kernel/time/timer.c:1504
 expire_timers kernel/time/timer.c:1549 [inline]
 __run_timers+0x525/0x7c0 kernel/time/timer.c:1820
 run_timer_softirq+0x63/0xf0 kernel/time/timer.c:1833
 handle_softirqs+0x2a1/0x920 kernel/softirq.c:578
 __do_softirq kernel/softirq.c:612 [inline]
 invoke_softirq kernel/softirq.c:452 [inline]
 __irq_exit_rcu+0x12f/0x220 kernel/softirq.c:661
 irq_exit_rcu+0x5/0x20 kernel/softirq.c:673
 instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1118 [inline]
 sysvec_apic_timer_interrupt+0xa0/0xc0 arch/x86/kernel/apic/apic.c:1118
 </IRQ>
 <TASK>
 asm_sysvec_apic_timer_interrupt+0x16/0x20 arch/x86/include/asm/idtentry.h:691
RIP: 0010:finish_task_switch+0x26a/0x8f0 kernel/sched/core.c:5123
Code: 0f 84 3b 01 00 00 48 85 db 0f 85 5a 01 00 00 0f 1f 44 00 00 4c 8b 75 d0 4c 89 e7 e8 e0 b9 c0 08 e8 eb c1 2e 00 fb 4c 8b 65 c0 <49> 8d bc 24 f8 15 00 00 48 89 f8 48 c1 e8 03 42 0f b6 04 28 84 c0
RSP: 0018:ffffc9000c60f338 EFLAGS: 00000282
RAX: e818486bd3ab6e00 RBX: 0000000000000000 RCX: e818486bd3ab6e00
RDX: dffffc0000000000 RSI: ffffffff8a6c0000 RDI: ffffffff8abf1020
RBP: ffffc9000c60f390 R08: dffffc0000000000 R09: ffffed10171e7549
R10: ffffed10171e7549 R11: 1ffff110171e7548 R12: ffff8880192c5940
R13: dffffc0000000000 R14: ffff8880192c0000 R15: 0000000000000000
 context_switch kernel/sched/core.c:5247 [inline]
 __schedule+0x10f1/0x40d0 kernel/sched/core.c:6561
 schedule+0xb9/0x180 kernel/sched/core.c:6637
 schedule_timeout+0x97/0x280 kernel/time/timer.c:1941
 unix_wait_for_peer+0x1e5/0x2e0 net/unix/af_unix.c:1443
 unix_dgram_sendmsg+0x102d/0x18d0 net/unix/af_unix.c:2022
 sock_sendmsg_nosec net/socket.c:718 [inline]
 __sock_sendmsg net/socket.c:730 [inline]
 ____sys_sendmsg+0x59b/0x970 net/socket.c:2519
 ___sys_sendmsg+0x21c/0x290 net/socket.c:2573
 __sys_sendmmsg+0x272/0x490 net/socket.c:2659
 __do_sys_sendmmsg net/socket.c:2688 [inline]
 __se_sys_sendmmsg net/socket.c:2685 [inline]
 __x64_sys_sendmmsg+0x9c/0xb0 net/socket.c:2685
 do_syscall_x64 arch/x86/entry/common.c:51 [inline]
 do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:81
 entry_SYSCALL_64_after_hwframe+0x68/0xd2
RIP: 0033:0x7f56fcb8e969
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:00007f56fd919038 EFLAGS: 00000246 ORIG_RAX: 0000000000000133
RAX: ffffffffffffffda RBX: 00007f56fcdb5fa0 RCX: 00007f56fcb8e969
RDX: 0000000000000651 RSI: 0000200000000000 RDI: 0000000000000005
RBP: 00007f56fcc10ab1 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 0000000000000000 R14: 00007f56fcdb5fa0 R15: 00007ffeb5507d58
 </TASK>
----------------
Code disassembly (best guess):
   0:	0f 84 3b 01 00 00    	je     0x141
   6:	48 85 db             	test   %rbx,%rbx
   9:	0f 85 5a 01 00 00    	jne    0x169
   f:	0f 1f 44 00 00       	nopl   0x0(%rax,%rax,1)
  14:	4c 8b 75 d0          	mov    -0x30(%rbp),%r14
  18:	4c 89 e7             	mov    %r12,%rdi
  1b:	e8 e0 b9 c0 08       	call   0x8c0ba00
  20:	e8 eb c1 2e 00       	call   0x2ec210
  25:	fb                   	sti
  26:	4c 8b 65 c0          	mov    -0x40(%rbp),%r12
* 2a:	49 8d bc 24 f8 15 00 	lea    0x15f8(%r12),%rdi <-- trapping instruction
  31:	00
  32:	48 89 f8             	mov    %rdi,%rax
  35:	48 c1 e8 03          	shr    $0x3,%rax
  39:	42 0f b6 04 28       	movzbl (%rax,%r13,1),%eax
  3e:	84 c0                	test   %al,%al