============================================ WARNING: possible recursive locking detected syzkaller #0 Not tainted -------------------------------------------- kworker/1:8/16073 is trying to acquire lock: ffff888031070558 (&qdisc_xmit_lock_key#4){+.-.}-{3:3}, at: spin_lock include/linux/spinlock.h:351 [inline] ffff888031070558 (&qdisc_xmit_lock_key#4){+.-.}-{3:3}, at: __netif_tx_lock include/linux/netdevice.h:4685 [inline] ffff888031070558 (&qdisc_xmit_lock_key#4){+.-.}-{3:3}, at: sch_direct_xmit+0x3ba/0xcf0 net/sched/sch_generic.c:345 but task is already holding lock: ffff88805777ed58 (&qdisc_xmit_lock_key#4){+.-.}-{3:3}, at: spin_lock include/linux/spinlock.h:351 [inline] ffff88805777ed58 (&qdisc_xmit_lock_key#4){+.-.}-{3:3}, at: __netif_tx_lock include/linux/netdevice.h:4685 [inline] ffff88805777ed58 (&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 12 locks held by kworker/1:8/16073: #0: ffff888030a53148 ((wq_completion)mld){+.+.}-{0:0}, at: process_one_work+0x12a2/0x1b70 kernel/workqueue.c:3238 #1: ffffc90004c07d00 ((work_completion)(&(&idev->mc_ifc_work)->work)){+.+.}-{0:0}, at: process_one_work+0x929/0x1b70 kernel/workqueue.c:3239 #2: ffff8880561d0538 (&idev->mc_lock){+.+.}-{4:4}, at: mld_ifc_work+0x42/0xbf0 net/ipv6/mcast.c:2692 #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: mld_sendpack+0x1af/0x1350 net/ipv6/mcast.c:1827 #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: ip6_output+0xe3/0x710 net/ipv6/ip6_output.c:235 #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: ffff88805777ed58 (&qdisc_xmit_lock_key#4){+.-.}-{3:3}, at: spin_lock include/linux/spinlock.h:351 [inline] #6: ffff88805777ed58 (&qdisc_xmit_lock_key#4){+.-.}-{3:3}, at: __netif_tx_lock include/linux/netdevice.h:4685 [inline] #6: ffff88805777ed58 (&qdisc_xmit_lock_key#4){+.-.}-{3:3}, at: __dev_queue_xmit+0x1d9d/0x4490 net/core/dev.c:4759 #7: ffffffff8e3c4760 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:331 [inline] #7: ffffffff8e3c4760 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:867 [inline] #7: ffffffff8e3c4760 (rcu_read_lock){....}-{1:3}, at: ip_output+0x60/0xa90 net/ipv4/ip_output.c:433 #8: ffffffff8e3c4760 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:331 [inline] #8: ffffffff8e3c4760 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:867 [inline] #8: ffffffff8e3c4760 (rcu_read_lock){....}-{1:3}, at: ip_finish_output2+0x356/0x21a0 net/ipv4/ip_output.c:230 #9: ffffffff8e3c4760 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:331 [inline] #9: ffffffff8e3c4760 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:867 [inline] #9: ffffffff8e3c4760 (rcu_read_lock){....}-{1:3}, at: arp_xmit+0x26/0x2e0 net/ipv4/arp.c:662 #10: ffffffff8e3c4700 (rcu_read_lock_bh){....}-{1:3}, at: local_bh_disable include/linux/bottom_half.h:20 [inline] #10: ffffffff8e3c4700 (rcu_read_lock_bh){....}-{1:3}, at: rcu_read_lock_bh include/linux/rcupdate.h:918 [inline] #10: ffffffff8e3c4700 (rcu_read_lock_bh){....}-{1:3}, at: __dev_queue_xmit+0x276/0x4490 net/core/dev.c:4688 #11: ffff888023f01258 (dev->qdisc_tx_busylock ?: &qdisc_tx_busylock#3){+...}-{3:3}, at: spin_trylock include/linux/spinlock.h:361 [inline] #11: ffff888023f01258 (dev->qdisc_tx_busylock ?: &qdisc_tx_busylock#3){+...}-{3:3}, at: qdisc_run_begin include/net/sch_generic.h:197 [inline] #11: ffff888023f01258 (dev->qdisc_tx_busylock ?: &qdisc_tx_busylock#3){+...}-{3:3}, at: qdisc_run_begin include/net/sch_generic.h:194 [inline] #11: ffff888023f01258 (dev->qdisc_tx_busylock ?: &qdisc_tx_busylock#3){+...}-{3:3}, at: __dev_xmit_skb net/core/dev.c:4139 [inline] #11: ffff888023f01258 (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: 16073 Comm: kworker/1:8 Not tainted syzkaller #0 PREEMPT(full) Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025 Workqueue: mld mld_ifc_work 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:345 __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 neigh_output include/net/neighbour.h:547 [inline] ip6_finish_output2+0xad1/0x1cf0 net/ipv6/ip6_output.c:136 __ip6_finish_output+0x3cd/0x1010 net/ipv6/ip6_output.c:209 ip6_finish_output net/ipv6/ip6_output.c:220 [inline] NF_HOOK_COND include/linux/netfilter.h:307 [inline] ip6_output+0x253/0x710 net/ipv6/ip6_output.c:247 dst_output include/net/dst.h:464 [inline] NF_HOOK include/linux/netfilter.h:318 [inline] NF_HOOK include/linux/netfilter.h:312 [inline] mld_sendpack+0xac1/0x1350 net/ipv6/mcast.c:1855 mld_send_cr net/ipv6/mcast.c:2154 [inline] mld_ifc_work+0x740/0xbf0 net/ipv6/mcast.c:2693 process_one_work+0x9cf/0x1b70 kernel/workqueue.c:3263 process_scheduled_works kernel/workqueue.c:3346 [inline] worker_thread+0x6c8/0xf10 kernel/workqueue.c:3427 kthread+0x3c5/0x780 kernel/kthread.c:463 ret_from_fork+0x675/0x7d0 arch/x86/kernel/process.c:158 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245