syzbot

======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Tainted: G             L     
------------------------------------------------------
kworker/1:9/18979 is trying to acquire lock:
ffff888057dc2d58 (&qdisc_xmit_lock_key#4){+.-.}-{3:3}, at: spin_lock include/linux/spinlock.h:342 [inline]
ffff888057dc2d58 (&qdisc_xmit_lock_key#4){+.-.}-{3:3}, at: __netif_tx_lock include/linux/netdevice.h:4781 [inline]
ffff888057dc2d58 (&qdisc_xmit_lock_key#4){+.-.}-{3:3}, at: sch_direct_xmit+0x15f/0x4c0 net/sched/sch_generic.c:370

but task is already holding lock:
ffff88802b61cff0 (&hsr->seqnr_lock){+.-.}-{3:3}, at: spin_lock_bh include/linux/spinlock.h:348 [inline]
ffff88802b61cff0 (&hsr->seqnr_lock){+.-.}-{3:3}, at: hsr_dev_xmit+0x237/0x360 net/hsr/hsr_device.c:235

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #1 (&hsr->seqnr_lock){+.-.}-{3:3}:
       __raw_spin_lock_bh include/linux/spinlock_api_smp.h:150 [inline]
       _raw_spin_lock_bh+0x36/0x50 kernel/locking/spinlock.c:182
       spin_lock_bh include/linux/spinlock.h:348 [inline]
       hsr_dev_xmit+0x237/0x360 net/hsr/hsr_device.c:235
       __netdev_start_xmit include/linux/netdevice.h:5368 [inline]
       netdev_start_xmit include/linux/netdevice.h:5377 [inline]
       xmit_one net/core/dev.c:3888 [inline]
       dev_hard_start_xmit+0x2cd/0x830 net/core/dev.c:3904
       __dev_queue_xmit+0x14d9/0x3950 net/core/dev.c:4870
       NF_HOOK+0x33a/0x3c0 include/linux/netfilter.h:-1
       arp_xmit+0x16c/0x270 net/ipv4/arp.c:665
       arp_solicit+0xbe0/0xe40 net/ipv4/arp.c:392
       neigh_probe net/core/neighbour.c:1096 [inline]
       __neigh_event_send+0xf05/0x14d0 net/core/neighbour.c:1276
       neigh_event_send_probe include/net/neighbour.h:480 [inline]
       neigh_event_send include/net/neighbour.h:486 [inline]
       neigh_resolve_output+0x198/0x750 net/core/neighbour.c:1603
       neigh_output include/net/neighbour.h:560 [inline]
       ip_finish_output2+0xca9/0x1070 net/ipv4/ip_output.c:237
       NF_HOOK_COND include/linux/netfilter.h:307 [inline]
       ip_output+0x29f/0x450 net/ipv4/ip_output.c:438
       iptunnel_xmit+0x621/0xd10 net/ipv4/ip_tunnel_core.c:97
       ip_tunnel_xmit+0x193a/0x1f20 net/ipv4/ip_tunnel.c:845
       __gre_xmit+0x19e/0x240 net/ipv4/ip_gre.c:491
       erspan_xmit+0xa41/0x14d0 net/ipv4/ip_gre.c:750
       __netdev_start_xmit include/linux/netdevice.h:5368 [inline]
       netdev_start_xmit include/linux/netdevice.h:5377 [inline]
       xmit_one net/core/dev.c:3888 [inline]
       dev_hard_start_xmit+0x2cd/0x830 net/core/dev.c:3904
       sch_direct_xmit+0x251/0x4c0 net/sched/sch_generic.c:372
       __dev_xmit_skb net/core/dev.c:4209 [inline]
       __dev_queue_xmit+0x180f/0x3950 net/core/dev.c:4831
       NF_HOOK_COND include/linux/netfilter.h:307 [inline]
       ip6_output+0x340/0x550 net/ipv6/ip6_output.c:246
       dst_output include/net/dst.h:470 [inline]
       NF_HOOK include/linux/netfilter.h:318 [inline]
       ndisc_send_skb+0xd0b/0x1670 net/ipv6/ndisc.c:512
       addrconf_rs_timer+0x395/0x6d0 net/ipv6/addrconf.c:4049
       call_timer_fn+0x192/0x5e0 kernel/time/timer.c:1748
       expire_timers kernel/time/timer.c:1799 [inline]
       __run_timers kernel/time/timer.c:2374 [inline]
       __run_timer_base+0x652/0x8b0 kernel/time/timer.c:2386
       run_timer_base kernel/time/timer.c:2395 [inline]
       run_timer_softirq+0xb7/0x170 kernel/time/timer.c:2405
       handle_softirqs+0x22a/0x840 kernel/softirq.c:622
       __do_softirq kernel/softirq.c:656 [inline]
       invoke_softirq kernel/softirq.c:496 [inline]
       __irq_exit_rcu+0xca/0x220 kernel/softirq.c:735
       irq_exit_rcu+0x9/0x30 kernel/softirq.c:752
       instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1061 [inline]
       sysvec_apic_timer_interrupt+0xa6/0xc0 arch/x86/kernel/apic/apic.c:1061
       asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:697
       native_safe_halt arch/x86/include/asm/irqflags.h:48 [inline]
       pv_native_safe_halt+0xf/0x20 arch/x86/kernel/paravirt.c:62
       arch_safe_halt arch/x86/kernel/process.c:766 [inline]
       default_idle+0x9/0x20 arch/x86/kernel/process.c:767
       default_idle_call+0x72/0xb0 kernel/sched/idle.c:122
       cpuidle_idle_call kernel/sched/idle.c:199 [inline]
       do_idle+0x36a/0x5f0 kernel/sched/idle.c:352
       cpu_startup_entry+0x43/0x60 kernel/sched/idle.c:451
       start_secondary+0x101/0x110 arch/x86/kernel/smpboot.c:312
       common_startup_64+0x13e/0x147

-> #0 (&qdisc_xmit_lock_key#4){+.-.}-{3:3}:
       check_prev_add kernel/locking/lockdep.c:3165 [inline]
       check_prevs_add kernel/locking/lockdep.c:3284 [inline]
       validate_chain kernel/locking/lockdep.c:3908 [inline]
       __lock_acquire+0x15a5/0x2cf0 kernel/locking/lockdep.c:5237
       lock_acquire+0x106/0x350 kernel/locking/lockdep.c:5868
       __raw_spin_lock include/linux/spinlock_api_smp.h:158 [inline]
       _raw_spin_lock+0x2e/0x40 kernel/locking/spinlock.c:158
       spin_lock include/linux/spinlock.h:342 [inline]
       __netif_tx_lock include/linux/netdevice.h:4781 [inline]
       sch_direct_xmit+0x15f/0x4c0 net/sched/sch_generic.c:370
       __dev_xmit_skb net/core/dev.c:4209 [inline]
       __dev_queue_xmit+0x180f/0x3950 net/core/dev.c:4831
       dev_queue_xmit include/linux/netdevice.h:3418 [inline]
       hsr_xmit net/hsr/hsr_forward.c:440 [inline]
       hsr_forward_do net/hsr/hsr_forward.c:581 [inline]
       hsr_forward_skb+0x167e/0x2ab0 net/hsr/hsr_forward.c:743
       hsr_dev_xmit+0x242/0x360 net/hsr/hsr_device.c:236
       __netdev_start_xmit include/linux/netdevice.h:5368 [inline]
       netdev_start_xmit include/linux/netdevice.h:5377 [inline]
       xmit_one net/core/dev.c:3888 [inline]
       dev_hard_start_xmit+0x2cd/0x830 net/core/dev.c:3904
       __dev_queue_xmit+0x14d9/0x3950 net/core/dev.c:4870
       NF_HOOK_COND include/linux/netfilter.h:307 [inline]
       ip6_output+0x340/0x550 net/ipv6/ip6_output.c:246
       dst_output include/net/dst.h:470 [inline]
       NF_HOOK+0x177/0x4f0 include/linux/netfilter.h:318
       mld_sendpack+0x8b4/0xe40 net/ipv6/mcast.c:1855
       mld_send_cr net/ipv6/mcast.c:2154 [inline]
       mld_ifc_work+0x835/0xe70 net/ipv6/mcast.c:2693
       process_one_work kernel/workqueue.c:3314 [inline]
       process_scheduled_works+0xb5d/0x1860 kernel/workqueue.c:3397
       worker_thread+0xa53/0xfc0 kernel/workqueue.c:3478
       kthread+0x389/0x470 kernel/kthread.c:436
       ret_from_fork+0x514/0xb70 arch/x86/kernel/process.c:158
       ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

other info that might help us debug this:

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(&hsr->seqnr_lock);
                               lock(&qdisc_xmit_lock_key#4);
                               lock(&hsr->seqnr_lock);
  lock(&qdisc_xmit_lock_key#4);

 *** DEADLOCK ***

11 locks held by kworker/1:9/18979:
 #0: ffff8880319a3d40 ((wq_completion)mld){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:3289 [inline]
 #0: ffff8880319a3d40 ((wq_completion)mld){+.+.}-{0:0}, at: process_scheduled_works+0xa35/0x1860 kernel/workqueue.c:3397
 #1: ffffc900037afc40 ((work_completion)(&(&idev->mc_ifc_work)->work)){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:3290 [inline]
 #1: ffffc900037afc40 ((work_completion)(&(&idev->mc_ifc_work)->work)){+.+.}-{0:0}, at: process_scheduled_works+0xa70/0x1860 kernel/workqueue.c:3397
 #2: ffff8880782a6530 (&idev->mc_lock){+.+.}-{4:4}, at: mld_ifc_work+0x2d/0xe70 net/ipv6/mcast.c:2692
 #3: ffffffff8e95cd20 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:300 [inline]
 #3: ffffffff8e95cd20 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:838 [inline]
 #3: ffffffff8e95cd20 (rcu_read_lock){....}-{1:3}, at: mld_sendpack+0x213/0xe40 net/ipv6/mcast.c:1827
 #4: ffffffff8e95cd20 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:300 [inline]
 #4: ffffffff8e95cd20 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:838 [inline]
 #4: ffffffff8e95cd20 (rcu_read_lock){....}-{1:3}, at: ip6_output+0x126/0x550 net/ipv6/ip6_output.c:234
 #5: ffffffff8e95cd80 (rcu_read_lock_bh){....}-{1:3}, at: local_bh_disable include/linux/bottom_half.h:20 [inline]
 #5: ffffffff8e95cd80 (rcu_read_lock_bh){....}-{1:3}, at: rcu_read_lock_bh include/linux/rcupdate.h:891 [inline]
 #5: ffffffff8e95cd80 (rcu_read_lock_bh){....}-{1:3}, at: __dev_queue_xmit+0x2b6/0x3950 net/core/dev.c:4791
 #6: ffffffff8e95cd20 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:300 [inline]
 #6: ffffffff8e95cd20 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:838 [inline]
 #6: ffffffff8e95cd20 (rcu_read_lock){....}-{1:3}, at: hsr_dev_xmit+0x2d/0x360 net/hsr/hsr_device.c:229
 #7: ffff88802b61cff0 (&hsr->seqnr_lock){+.-.}-{3:3}, at: spin_lock_bh include/linux/spinlock.h:348 [inline]
 #7: ffff88802b61cff0 (&hsr->seqnr_lock){+.-.}-{3:3}, at: hsr_dev_xmit+0x237/0x360 net/hsr/hsr_device.c:235
 #8: ffffffff8e95cd20 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:300 [inline]
 #8: ffffffff8e95cd20 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:838 [inline]
 #8: ffffffff8e95cd20 (rcu_read_lock){....}-{1:3}, at: hsr_forward_skb+0xbb/0x2ab0 net/hsr/hsr_forward.c:738
 #9: ffffffff8e95cd80 (rcu_read_lock_bh){....}-{1:3}, at: local_bh_disable include/linux/bottom_half.h:20 [inline]
 #9: ffffffff8e95cd80 (rcu_read_lock_bh){....}-{1:3}, at: rcu_read_lock_bh include/linux/rcupdate.h:891 [inline]
 #9: ffffffff8e95cd80 (rcu_read_lock_bh){....}-{1:3}, at: __dev_queue_xmit+0x2b6/0x3950 net/core/dev.c:4791
 #10: ffff888028f5b228 (dev->qdisc_tx_busylock ?: &qdisc_tx_busylock#5){+...}-{3:3}, at: spin_trylock include/linux/spinlock.h:354 [inline]
 #10: ffff888028f5b228 (dev->qdisc_tx_busylock ?: &qdisc_tx_busylock#5){+...}-{3:3}, at: qdisc_run_begin include/net/sch_generic.h:205 [inline]
 #10: ffff888028f5b228 (dev->qdisc_tx_busylock ?: &qdisc_tx_busylock#5){+...}-{3:3}, at: __dev_xmit_skb net/core/dev.c:4196 [inline]
 #10: ffff888028f5b228 (dev->qdisc_tx_busylock ?: &qdisc_tx_busylock#5){+...}-{3:3}, at: __dev_queue_xmit+0x11a6/0x3950 net/core/dev.c:4831

stack backtrace:
CPU: 1 UID: 0 PID: 18979 Comm: kworker/1:9 Tainted: G             L      syzkaller #0 PREEMPT(full) 
Tainted: [L]=SOFTLOCKUP
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/09/2026
Workqueue: mld mld_ifc_work
Call Trace:
 <TASK>
 dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
 print_circular_bug+0x2e1/0x300 kernel/locking/lockdep.c:2043
 check_noncircular+0x12e/0x150 kernel/locking/lockdep.c:2175
 check_prev_add kernel/locking/lockdep.c:3165 [inline]
 check_prevs_add kernel/locking/lockdep.c:3284 [inline]
 validate_chain kernel/locking/lockdep.c:3908 [inline]
 __lock_acquire+0x15a5/0x2cf0 kernel/locking/lockdep.c:5237
 lock_acquire+0x106/0x350 kernel/locking/lockdep.c:5868
 __raw_spin_lock include/linux/spinlock_api_smp.h:158 [inline]
 _raw_spin_lock+0x2e/0x40 kernel/locking/spinlock.c:158
 spin_lock include/linux/spinlock.h:342 [inline]
 __netif_tx_lock include/linux/netdevice.h:4781 [inline]
 sch_direct_xmit+0x15f/0x4c0 net/sched/sch_generic.c:370
 __dev_xmit_skb net/core/dev.c:4209 [inline]
 __dev_queue_xmit+0x180f/0x3950 net/core/dev.c:4831
 dev_queue_xmit include/linux/netdevice.h:3418 [inline]
 hsr_xmit net/hsr/hsr_forward.c:440 [inline]
 hsr_forward_do net/hsr/hsr_forward.c:581 [inline]
 hsr_forward_skb+0x167e/0x2ab0 net/hsr/hsr_forward.c:743
 hsr_dev_xmit+0x242/0x360 net/hsr/hsr_device.c:236
 __netdev_start_xmit include/linux/netdevice.h:5368 [inline]
 netdev_start_xmit include/linux/netdevice.h:5377 [inline]
 xmit_one net/core/dev.c:3888 [inline]
 dev_hard_start_xmit+0x2cd/0x830 net/core/dev.c:3904
 __dev_queue_xmit+0x14d9/0x3950 net/core/dev.c:4870
 NF_HOOK_COND include/linux/netfilter.h:307 [inline]
 ip6_output+0x340/0x550 net/ipv6/ip6_output.c:246
 dst_output include/net/dst.h:470 [inline]
 NF_HOOK+0x177/0x4f0 include/linux/netfilter.h:318
 mld_sendpack+0x8b4/0xe40 net/ipv6/mcast.c:1855
 mld_send_cr net/ipv6/mcast.c:2154 [inline]
 mld_ifc_work+0x835/0xe70 net/ipv6/mcast.c:2693
 process_one_work kernel/workqueue.c:3314 [inline]
 process_scheduled_works+0xb5d/0x1860 kernel/workqueue.c:3397
 worker_thread+0xa53/0xfc0 kernel/workqueue.c:3478
 kthread+0x389/0x470 kernel/kthread.c:436
 ret_from_fork+0x514/0xb70 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
 </TASK>
usb 4-1: USB disconnect, device number 106