Kernel bug: possible deadlock in sch_direct_xmit (5)
Subsystem: net
Status: fixed

Crash report:
============================================
WARNING: possible recursive locking detected
syzkaller #0 Not tainted
--------------------------------------------
kworker/0:1/10 is trying to acquire lock:
ffff888079139d58 (&qdisc_xmit_lock_key#3){+...}-{3:3}, at: spin_lock include/linux/spinlock.h:351 [inline]
ffff888079139d58 (&qdisc_xmit_lock_key#3){+...}-{3:3}, at: __netif_tx_lock include/linux/netdevice.h:4659 [inline]
ffff888079139d58 (&qdisc_xmit_lock_key#3){+...}-{3:3}, at: sch_direct_xmit+0x153/0x4b0 net/sched/sch_generic.c:342

but task is already holding lock:
ffff88807de56158 (&qdisc_xmit_lock_key#3){+...}-{3:3}, at: spin_lock include/linux/spinlock.h:351 [inline]
ffff88807de56158 (&qdisc_xmit_lock_key#3){+...}-{3:3}, at: __netif_tx_lock include/linux/netdevice.h:4659 [inline]
ffff88807de56158 (&qdisc_xmit_lock_key#3){+...}-{3:3}, at: __dev_queue_xmit+0x1676/0x3b50 net/core/dev.c:4721

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

       CPU0
       ----
  lock(&qdisc_xmit_lock_key#3);
  lock(&qdisc_xmit_lock_key#3);

 *** DEADLOCK ***

 May be due to missing lock nesting notation

12 locks held by kworker/0:1/10:
 #0: ffff88802f2e1548 ((wq_completion)mld){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:3211 [inline]
 #0: ffff88802f2e1548 ((wq_completion)mld){+.+.}-{0:0}, at: process_scheduled_works+0x9b4/0x17b0 kernel/workqueue.c:3319
 #1: ffffc900000f7bc0 ((work_completion)(&(&idev->mc_ifc_work)->work)){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:3212 [inline]
 #1: ffffc900000f7bc0 ((work_completion)(&(&idev->mc_ifc_work)->work)){+.+.}-{0:0}, at: process_scheduled_works+0x9ef/0x17b0 kernel/workqueue.c:3319
 #2: ffff888079a43538 (&idev->mc_lock){+.+.}-{4:4}, at: mld_ifc_work+0x2d/0xd60 net/ipv6/mcast.c:2697
 #3: ffffffff8e13a0e0 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:331 [inline]
 #3: ffffffff8e13a0e0 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:841 [inline]
 #3: ffffffff8e13a0e0 (rcu_read_lock){....}-{1:3}, at: mld_sendpack+0x1de/0xd80 net/ipv6/mcast.c:1832
 #4: ffffffff8e13a0e0 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:331 [inline]
 #4: ffffffff8e13a0e0 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:841 [inline]
 #4: ffffffff8e13a0e0 (rcu_read_lock){....}-{1:3}, at: ip6_finish_output2+0x701/0x16a0 net/ipv6/ip6_output.c:126
 #5: ffffffff8e13a140 (rcu_read_lock_bh){....}-{1:3}, at: local_bh_disable include/linux/bottom_half.h:20 [inline]
 #5: ffffffff8e13a140 (rcu_read_lock_bh){....}-{1:3}, at: rcu_read_lock_bh include/linux/rcupdate.h:892 [inline]
 #5: ffffffff8e13a140 (rcu_read_lock_bh){....}-{1:3}, at: __dev_queue_xmit+0x27b/0x3b50 net/core/dev.c:4650
 #6: ffff88807de56158 (&qdisc_xmit_lock_key#3){+...}-{3:3}, at: spin_lock include/linux/spinlock.h:351 [inline]
 #6: ffff88807de56158 (&qdisc_xmit_lock_key#3){+...}-{3:3}, at: __netif_tx_lock include/linux/netdevice.h:4659 [inline]
 #6: ffff88807de56158 (&qdisc_xmit_lock_key#3){+...}-{3:3}, at: __dev_queue_xmit+0x1676/0x3b50 net/core/dev.c:4721
 #7: ffffffff8e13a0e0 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:331 [inline]
 #7: ffffffff8e13a0e0 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:841 [inline]
 #7: ffffffff8e13a0e0 (rcu_read_lock){....}-{1:3}, at: ip_output+0x60/0x3c0 net/ipv4/ip_output.c:431
 #8: ffffffff8e13a0e0 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:331 [inline]
 #8: ffffffff8e13a0e0 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:841 [inline]
 #8: ffffffff8e13a0e0 (rcu_read_lock){....}-{1:3}, at: ip_finish_output2+0x452/0x1160 net/ipv4/ip_output.c:228
 #9: ffffffff8e13a0e0 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:331 [inline]
 #9: ffffffff8e13a0e0 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:841 [inline]
 #9: ffffffff8e13a0e0 (rcu_read_lock){....}-{1:3}, at: arp_xmit+0x23/0x270 net/ipv4/arp.c:662
 #10: ffffffff8e13a140 (rcu_read_lock_bh){....}-{1:3}, at: local_bh_disable include/linux/bottom_half.h:20 [inline]
 #10: ffffffff8e13a140 (rcu_read_lock_bh){....}-{1:3}, at: rcu_read_lock_bh include/linux/rcupdate.h:892 [inline]
 #10: ffffffff8e13a140 (rcu_read_lock_bh){....}-{1:3}, at: __dev_queue_xmit+0x27b/0x3b50 net/core/dev.c:4650
 #11: ffff88807ec9a258 (dev->qdisc_tx_busylock ?: &qdisc_tx_busylock#3){+...}-{3:3}, at: spin_trylock include/linux/spinlock.h:361 [inline]
 #11: ffff88807ec9a258 (dev->qdisc_tx_busylock ?: &qdisc_tx_busylock#3){+...}-{3:3}, at: qdisc_run_begin include/net/sch_generic.h:197 [inline]
 #11: ffff88807ec9a258 (dev->qdisc_tx_busylock ?: &qdisc_tx_busylock#3){+...}-{3:3}, at: __dev_xmit_skb net/core/dev.c:4101 [inline]
 #11: ffff88807ec9a258 (dev->qdisc_tx_busylock ?: &qdisc_tx_busylock#3){+...}-{3:3}, at: __dev_queue_xmit+0x138a/0x3b50 net/core/dev.c:4691

stack backtrace:
CPU: 0 UID: 0 PID: 10 Comm: kworker/0:1 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/18/2025
Workqueue: mld mld_ifc_work
Call Trace:
 <TASK>
 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
 __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:4659 [inline]
 sch_direct_xmit+0x153/0x4b0 net/sched/sch_generic.c:342
 __dev_xmit_skb net/core/dev.c:4114 [inline]
 __dev_queue_xmit+0x1857/0x3b50 net/core/dev.c:4691
 NF_HOOK+0x310/0x3a0 include/linux/netfilter.h:-1
 arp_xmit+0x16c/0x270 net/ipv4/arp.c:664
 arp_solicit+0xc1d/0xe60 net/ipv4/arp.c:392
 neigh_probe net/core/neighbour.c:1098 [inline]
 __neigh_event_send+0xf6d/0x1560 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+0x198/0x750 net/core/neighbour.c:1579
 neigh_output include/net/neighbour.h:547 [inline]
 ip_finish_output2+0xd3d/0x1160 net/ipv4/ip_output.c:235
 NF_HOOK_COND include/linux/netfilter.h:307 [inline]
 ip_output+0x2a1/0x3c0 net/ipv4/ip_output.c:436
 iptunnel_xmit+0x592/0xa40 net/ipv4/ip_tunnel_core.c:84
 ip_tunnel_xmit+0x1c41/0x2390 net/ipv4/ip_tunnel.c:859
 __gre_xmit net/ipv4/ip_gre.c:488 [inline]
 ipgre_xmit+0x89e/0xc50 net/ipv4/ip_gre.c:692
 __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+0x2d7/0x830 net/core/dev.c:3855
 __dev_queue_xmit+0x1b8d/0x3b50 net/core/dev.c:4725
 neigh_output include/net/neighbour.h:547 [inline]
 ip6_finish_output2+0x11fb/0x16a0 net/ipv6/ip6_output.c:141
 NF_HOOK+0x9e/0x380 include/linux/netfilter.h:318
 mld_sendpack+0x800/0xd80 net/ipv6/mcast.c:1860
 mld_send_cr net/ipv6/mcast.c:2159 [inline]
 mld_ifc_work+0x83e/0xd60 net/ipv6/mcast.c:2698
 process_one_work kernel/workqueue.c:3236 [inline]
 process_scheduled_works+0xae1/0x17b0 kernel/workqueue.c:3319
 worker_thread+0x8a0/0xda0 kernel/workqueue.c:3400
 kthread+0x70e/0x8a0 kernel/kthread.c:463
 ret_from_fork+0x436/0x7d0 arch/x86/kernel/process.c:148
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
 </TASK>