============================================ WARNING: possible recursive locking detected syzkaller #0 Not tainted -------------------------------------------- kworker/1:4/4195 is trying to acquire lock: ffff88807dd5e218 (dev->qdisc_tx_busylock ?: &qdisc_tx_busylock){+...}-{2:2}, at: spin_lock include/linux/spinlock.h:363 [inline] ffff88807dd5e218 (dev->qdisc_tx_busylock ?: &qdisc_tx_busylock){+...}-{2:2}, at: __dev_xmit_skb net/core/dev.c:3909 [inline] ffff88807dd5e218 (dev->qdisc_tx_busylock ?: &qdisc_tx_busylock){+...}-{2:2}, at: __dev_queue_xmit+0x1f6e/0x2ed0 net/core/dev.c:4253 but task is already holding lock: ffff88807de11258 (dev->qdisc_tx_busylock ?: &qdisc_tx_busylock){+...}-{2:2}, at: spin_trylock include/linux/spinlock.h:373 [inline] ffff88807de11258 (dev->qdisc_tx_busylock ?: &qdisc_tx_busylock){+...}-{2:2}, at: qdisc_run_begin include/net/sch_generic.h:173 [inline] ffff88807de11258 (dev->qdisc_tx_busylock ?: &qdisc_tx_busylock){+...}-{2:2}, at: __dev_xmit_skb net/core/dev.c:3871 [inline] ffff88807de11258 (dev->qdisc_tx_busylock ?: &qdisc_tx_busylock){+...}-{2:2}, at: __dev_queue_xmit+0x10b9/0x2ed0 net/core/dev.c:4253 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 15 locks held by kworker/1:4/4195: #0: ffff88802a902138 ((wq_completion)mld){+.+.}-{0:0}, at: process_one_work+0x760/0x1000 kernel/workqueue.c:-1 #1: ffffc90002f1fd00 ((work_completion)(&(&idev->mc_ifc_work)->work)){+.+.}-{0:0}, at: process_one_work+0x7a3/0x1000 kernel/workqueue.c:2285 #2: ffff88807bf40530 (&idev->mc_lock){+.+.}-{3:3}, at: mld_ifc_work+0x29/0xb40 net/ipv6/mcast.c:2657 #3: ffffffff8c11c660 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire+0x5/0x30 include/linux/rcupdate.h:311 #4: ffffffff8c11c6c0 (rcu_read_lock_bh){....}-{1:2}, at: rcu_lock_acquire+0x9/0x30 include/linux/rcupdate.h:312 #5: ffffffff8c11c6c0 (rcu_read_lock_bh){....}-{1:2}, at: rcu_lock_acquire+0x9/0x30 include/linux/rcupdate.h:312 #6: ffff88807de11258 (dev->qdisc_tx_busylock ?: &qdisc_tx_busylock){+...}-{2:2}, at: spin_trylock include/linux/spinlock.h:373 [inline] #6: ffff88807de11258 (dev->qdisc_tx_busylock ?: &qdisc_tx_busylock){+...}-{2:2}, at: qdisc_run_begin include/net/sch_generic.h:173 [inline] #6: ffff88807de11258 (dev->qdisc_tx_busylock ?: &qdisc_tx_busylock){+...}-{2:2}, at: __dev_xmit_skb net/core/dev.c:3871 [inline] #6: ffff88807de11258 (dev->qdisc_tx_busylock ?: &qdisc_tx_busylock){+...}-{2:2}, at: __dev_queue_xmit+0x10b9/0x2ed0 net/core/dev.c:4253 #7: ffffffff8c11c6c0 (rcu_read_lock_bh){....}-{1:2}, at: rcu_lock_acquire+0x9/0x30 include/linux/rcupdate.h:312 #8: ffffffff8c11c6c0 (rcu_read_lock_bh){....}-{1:2}, at: rcu_lock_acquire+0x9/0x30 include/linux/rcupdate.h:312 #9: ffff88807dd5e148 (dev->qdisc_running_key ?: &qdisc_running_key){+...}-{0:0}, at: neigh_output include/net/neighbour.h:509 [inline] #9: ffff88807dd5e148 (dev->qdisc_running_key ?: &qdisc_running_key){+...}-{0:0}, at: ip6_finish_output2+0x1070/0x1500 net/ipv6/ip6_output.c:130 #10: ffff8880195e9da0 (k-slock-AF_INET6){+...}-{2:2}, at: spin_trylock include/linux/spinlock.h:373 [inline] #10: ffff8880195e9da0 (k-slock-AF_INET6){+...}-{2:2}, at: icmpv6_xmit_lock net/ipv6/icmp.c:118 [inline] #10: ffff8880195e9da0 (k-slock-AF_INET6){+...}-{2:2}, at: icmp6_send+0xa93/0x16e0 net/ipv6/icmp.c:551 #11: ffffffff8c11c660 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire+0x5/0x30 include/linux/rcupdate.h:311 #12: ffffffff8c11c660 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire+0x9/0x30 include/linux/rcupdate.h:312 #13: ffffffff8c11c6c0 (rcu_read_lock_bh){....}-{1:2}, at: rcu_lock_acquire+0x9/0x30 include/linux/rcupdate.h:312 #14: ffffffff8c11c6c0 (rcu_read_lock_bh){....}-{1:2}, at: rcu_lock_acquire+0x9/0x30 include/linux/rcupdate.h:312 stack backtrace: CPU: 1 PID: 4195 Comm: kworker/1:4 Not tainted syzkaller #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/12/2025 Workqueue: mld mld_ifc_work Call Trace: dump_stack_lvl+0x168/0x230 lib/dump_stack.c:106 __lock_acquire+0x1227/0x7c60 kernel/locking/lockdep.c:-1 lock_acquire+0x197/0x3f0 kernel/locking/lockdep.c:5623 __raw_spin_lock include/linux/spinlock_api_smp.h:142 [inline] _raw_spin_lock+0x2a/0x40 kernel/locking/spinlock.c:154 spin_lock include/linux/spinlock.h:363 [inline] __dev_xmit_skb net/core/dev.c:3909 [inline] __dev_queue_xmit+0x1f6e/0x2ed0 net/core/dev.c:4253 neigh_output include/net/neighbour.h:509 [inline] ip6_finish_output2+0x1070/0x1500 net/ipv6/ip6_output.c:130 ip6_send_skb+0x1b9/0x360 net/ipv6/ip6_output.c:1951 icmp6_send+0x113e/0x16e0 net/ipv6/icmp.c:630 __icmpv6_send include/linux/icmpv6.h:28 [inline] icmpv6_send include/linux/icmpv6.h:49 [inline] ip6_link_failure+0x35/0x490 net/ipv6/route.c:2788 dst_link_failure include/net/dst.h:422 [inline] ipip6_tunnel_xmit net/ipv6/sit.c:1045 [inline] sit_tunnel_xmit+0xa86/0x2250 net/ipv6/sit.c:1082 __netdev_start_xmit include/linux/netdevice.h:5027 [inline] netdev_start_xmit include/linux/netdevice.h:5041 [inline] xmit_one net/core/dev.c:3649 [inline] dev_hard_start_xmit+0x2a5/0x7e0 net/core/dev.c:3665 sch_direct_xmit+0x24e/0x4a0 net/sched/sch_generic.c:342 qdisc_restart net/sched/sch_generic.c:407 [inline] __qdisc_run+0xa74/0x1480 net/sched/sch_generic.c:415 __dev_xmit_skb net/core/dev.c:3942 [inline] __dev_queue_xmit+0xeb9/0x2ed0 net/core/dev.c:4253 neigh_output include/net/neighbour.h:509 [inline] ip6_finish_output2+0x1070/0x1500 net/ipv6/ip6_output.c:130 ip6tunnel_xmit+0x1a6/0x3d0 include/net/ip6_tunnel.h:160 ip6_tnl_xmit+0x1d6c/0x24a0 net/ipv6/ip6_tunnel.c:1271 __gre6_xmit+0x960/0xc70 net/ipv6/ip6_gre.c:787 ip6gre_xmit_ipv6 net/ipv6/ip6_gre.c:843 [inline] ip6gre_tunnel_xmit+0xb35/0xf10 net/ipv6/ip6_gre.c:915 __netdev_start_xmit include/linux/netdevice.h:5027 [inline] netdev_start_xmit include/linux/netdevice.h:5041 [inline] xmit_one net/core/dev.c:3649 [inline] dev_hard_start_xmit+0x2a5/0x7e0 net/core/dev.c:3665 sch_direct_xmit+0x24e/0x4a0 net/sched/sch_generic.c:342 __dev_xmit_skb net/core/dev.c:3884 [inline] __dev_queue_xmit+0x170e/0x2ed0 net/core/dev.c:4253 neigh_output include/net/neighbour.h:509 [inline] ip6_finish_output2+0x1070/0x1500 net/ipv6/ip6_output.c:130 dst_output include/net/dst.h:452 [inline] NF_HOOK+0x15f/0x430 include/linux/netfilter.h:302 mld_sendpack+0x713/0xc30 net/ipv6/mcast.c:1825 mld_send_cr net/ipv6/mcast.c:2126 [inline] mld_ifc_work+0x836/0xb40 net/ipv6/mcast.c:2658 process_one_work+0x863/0x1000 kernel/workqueue.c:2310 worker_thread+0xaa8/0x12a0 kernel/workqueue.c:2457 kthread+0x436/0x520 kernel/kthread.c:334 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:287