GRED: Unable to relocate VQ 0x0 after dequeue, screwing up backlog ====================================================== WARNING: possible circular locking dependency detected syzkaller #0 Not tainted ------------------------------------------------------ syz.2.2424/14302 is trying to acquire lock: ffff88801abc8218 (dev->qdisc_tx_busylock ?: &qdisc_tx_busylock#3){+...}-{3:3}, at: spin_lock include/linux/spinlock.h:351 [inline] ffff88801abc8218 (dev->qdisc_tx_busylock ?: &qdisc_tx_busylock#3){+...}-{3:3}, at: __dev_xmit_skb net/core/dev.c:4148 [inline] ffff88801abc8218 (dev->qdisc_tx_busylock ?: &qdisc_tx_busylock#3){+...}-{3:3}, at: __dev_queue_xmit+0x22b7/0x3b50 net/core/dev.c:4691 but task is already holding lock: ffff8880786bd558 (&qdisc_xmit_lock_key#4){+.-.}-{3:3}, at: spin_lock include/linux/spinlock.h:351 [inline] ffff8880786bd558 (&qdisc_xmit_lock_key#4){+.-.}-{3:3}, at: __netif_tx_lock include/linux/netdevice.h:4659 [inline] ffff8880786bd558 (&qdisc_xmit_lock_key#4){+.-.}-{3:3}, at: sch_direct_xmit+0x153/0x4b0 net/sched/sch_generic.c:342 which lock already depends on the new lock. the existing dependency chain (in reverse order) is: -> #1 (&qdisc_xmit_lock_key#4){+.-.}-{3:3}: 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 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+0x439/0x7d0 arch/x86/kernel/process.c:148 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245 -> #0 (dev->qdisc_tx_busylock ?: &qdisc_tx_busylock#3){+...}-{3:3}: check_prev_add kernel/locking/lockdep.c:3165 [inline] check_prevs_add kernel/locking/lockdep.c:3284 [inline] validate_chain+0xb9b/0x2140 kernel/locking/lockdep.c:3908 __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] __dev_xmit_skb net/core/dev.c:4148 [inline] __dev_queue_xmit+0x22b7/0x3b50 net/core/dev.c:4691 neigh_output include/net/neighbour.h:547 [inline] ip6_finish_output2+0x11fb/0x16a0 net/ipv6/ip6_output.c:141 ip6_send_skb+0x1d5/0x390 net/ipv6/ip6_output.c:1984 icmp6_send+0x12c6/0x1940 net/ipv6/icmp.c:634 __icmpv6_send include/linux/icmpv6.h:28 [inline] icmpv6_send include/linux/icmpv6.h:49 [inline] ip6_link_failure+0x3b/0x4c0 net/ipv6/route.c:2843 ip_tunnel_xmit+0x175b/0x2390 net/ipv4/ip_tunnel.c:865 __gre_xmit+0x19a/0x240 net/ipv4/ip_gre.c:488 erspan_xmit+0xa04/0x1220 net/ipv4/ip_gre.c:747 __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 sch_direct_xmit+0x241/0x4b0 net/sched/sch_generic.c:344 qdisc_restart net/sched/sch_generic.c:409 [inline] __qdisc_run+0xb16/0x15f0 net/sched/sch_generic.c:417 __dev_xmit_skb net/core/dev.c:4183 [inline] __dev_queue_xmit+0x1056/0x3b50 net/core/dev.c:4691 neigh_output include/net/neighbour.h:547 [inline] ip6_finish_output2+0x11fb/0x16a0 net/ipv6/ip6_output.c:141 ip6_send_skb+0x1d5/0x390 net/ipv6/ip6_output.c:1984 udp_v6_send_skb+0xc17/0x1830 net/ipv6/udp.c:1439 udpv6_sendmsg+0x1baf/0x24b0 net/ipv6/udp.c:1730 sock_sendmsg_nosec net/socket.c:714 [inline] __sock_sendmsg+0xe5/0x270 net/socket.c:729 ____sys_sendmsg+0x52d/0x830 net/socket.c:2614 ___sys_sendmsg+0x21f/0x2a0 net/socket.c:2668 __sys_sendmmsg+0x227/0x430 net/socket.c:2757 __do_sys_sendmmsg net/socket.c:2784 [inline] __se_sys_sendmmsg net/socket.c:2781 [inline] __x64_sys_sendmmsg+0xa0/0xc0 net/socket.c:2781 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline] do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94 entry_SYSCALL_64_after_hwframe+0x77/0x7f other info that might help us debug this: Possible unsafe locking scenario: CPU0 CPU1 ---- ---- lock(&qdisc_xmit_lock_key#4); lock(dev->qdisc_tx_busylock ?: &qdisc_tx_busylock#3); lock(&qdisc_xmit_lock_key#4); lock(dev->qdisc_tx_busylock ?: &qdisc_tx_busylock#3); *** DEADLOCK *** 9 locks held by syz.2.2424/14302: #0: ffffffff8e13a0e0 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:331 [inline] #0: ffffffff8e13a0e0 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:841 [inline] #0: ffffffff8e13a0e0 (rcu_read_lock){....}-{1:3}, at: ip6_send_skb+0x10f/0x390 net/ipv6/ip6_output.c:1983 #1: ffffffff8e13a0e0 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:331 [inline] #1: ffffffff8e13a0e0 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:841 [inline] #1: ffffffff8e13a0e0 (rcu_read_lock){....}-{1:3}, at: ip6_finish_output2+0x701/0x16a0 net/ipv6/ip6_output.c:126 #2: ffffffff8e13a140 (rcu_read_lock_bh){....}-{1:3}, at: local_bh_disable include/linux/bottom_half.h:20 [inline] #2: ffffffff8e13a140 (rcu_read_lock_bh){....}-{1:3}, at: rcu_read_lock_bh include/linux/rcupdate.h:892 [inline] #2: ffffffff8e13a140 (rcu_read_lock_bh){....}-{1:3}, at: __dev_queue_xmit+0x27b/0x3b50 net/core/dev.c:4650 #3: ffff8880786bd558 (&qdisc_xmit_lock_key#4){+.-.}-{3:3}, at: spin_lock include/linux/spinlock.h:351 [inline] #3: ffff8880786bd558 (&qdisc_xmit_lock_key#4){+.-.}-{3:3}, at: __netif_tx_lock include/linux/netdevice.h:4659 [inline] #3: ffff8880786bd558 (&qdisc_xmit_lock_key#4){+.-.}-{3:3}, at: sch_direct_xmit+0x153/0x4b0 net/sched/sch_generic.c:342 #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: icmp6_send+0x1e9/0x1940 net/ipv6/icmp.c:479 #5: ffff88802f6981d8 (k-slock-AF_INET6){+.-.}-{3:3}, at: spin_trylock include/linux/spinlock.h:361 [inline] #5: ffff88802f6981d8 (k-slock-AF_INET6){+.-.}-{3:3}, at: icmpv6_xmit_lock net/ipv6/icmp.c:108 [inline] #5: ffff88802f6981d8 (k-slock-AF_INET6){+.-.}-{3:3}, at: icmp6_send+0xc5c/0x1940 net/ipv6/icmp.c:556 #6: ffffffff8e13a0e0 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:331 [inline] #6: ffffffff8e13a0e0 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:841 [inline] #6: ffffffff8e13a0e0 (rcu_read_lock){....}-{1:3}, at: ip6_send_skb+0x10f/0x390 net/ipv6/ip6_output.c:1983 #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: ip6_finish_output2+0x701/0x16a0 net/ipv6/ip6_output.c:126 #8: ffffffff8e13a140 (rcu_read_lock_bh){....}-{1:3}, at: local_bh_disable include/linux/bottom_half.h:20 [inline] #8: ffffffff8e13a140 (rcu_read_lock_bh){....}-{1:3}, at: rcu_read_lock_bh include/linux/rcupdate.h:892 [inline] #8: ffffffff8e13a140 (rcu_read_lock_bh){....}-{1:3}, at: __dev_queue_xmit+0x27b/0x3b50 net/core/dev.c:4650 stack backtrace: CPU: 0 UID: 0 PID: 14302 Comm: syz.2.2424 Not tainted syzkaller #0 PREEMPT(full) Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/18/2025 Call Trace: dump_stack_lvl+0x189/0x250 lib/dump_stack.c:120 print_circular_bug+0x2ee/0x310 kernel/locking/lockdep.c:2043 check_noncircular+0x134/0x160 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+0xb9b/0x2140 kernel/locking/lockdep.c:3908 __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] __dev_xmit_skb net/core/dev.c:4148 [inline] __dev_queue_xmit+0x22b7/0x3b50 net/core/dev.c:4691 neigh_output include/net/neighbour.h:547 [inline] ip6_finish_output2+0x11fb/0x16a0 net/ipv6/ip6_output.c:141 ip6_send_skb+0x1d5/0x390 net/ipv6/ip6_output.c:1984 icmp6_send+0x12c6/0x1940 net/ipv6/icmp.c:634 __icmpv6_send include/linux/icmpv6.h:28 [inline] icmpv6_send include/linux/icmpv6.h:49 [inline] ip6_link_failure+0x3b/0x4c0 net/ipv6/route.c:2843 ip_tunnel_xmit+0x175b/0x2390 net/ipv4/ip_tunnel.c:865 __gre_xmit+0x19a/0x240 net/ipv4/ip_gre.c:488 erspan_xmit+0xa04/0x1220 net/ipv4/ip_gre.c:747 __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 sch_direct_xmit+0x241/0x4b0 net/sched/sch_generic.c:344 qdisc_restart net/sched/sch_generic.c:409 [inline] __qdisc_run+0xb16/0x15f0 net/sched/sch_generic.c:417 __dev_xmit_skb net/core/dev.c:4183 [inline] __dev_queue_xmit+0x1056/0x3b50 net/core/dev.c:4691 neigh_output include/net/neighbour.h:547 [inline] ip6_finish_output2+0x11fb/0x16a0 net/ipv6/ip6_output.c:141 ip6_send_skb+0x1d5/0x390 net/ipv6/ip6_output.c:1984 udp_v6_send_skb+0xc17/0x1830 net/ipv6/udp.c:1439 udpv6_sendmsg+0x1baf/0x24b0 net/ipv6/udp.c:1730 sock_sendmsg_nosec net/socket.c:714 [inline] __sock_sendmsg+0xe5/0x270 net/socket.c:729 ____sys_sendmsg+0x52d/0x830 net/socket.c:2614 ___sys_sendmsg+0x21f/0x2a0 net/socket.c:2668 __sys_sendmmsg+0x227/0x430 net/socket.c:2757 __do_sys_sendmmsg net/socket.c:2784 [inline] __se_sys_sendmmsg net/socket.c:2781 [inline] __x64_sys_sendmmsg+0xa0/0xc0 net/socket.c:2781 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline] do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94 entry_SYSCALL_64_after_hwframe+0x77/0x7f RIP: 0033:0x7fc6b378ec29 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:00007fc6b46cd038 EFLAGS: 00000246 ORIG_RAX: 0000000000000133 RAX: ffffffffffffffda RBX: 00007fc6b39d5fa0 RCX: 00007fc6b378ec29 RDX: 0400000000000172 RSI: 0000200000003cc0 RDI: 0000000000000004 RBP: 00007fc6b3811e41 R08: 0000000000000000 R09: 0000000000000000 R10: 0000000004000000 R11: 0000000000000246 R12: 0000000000000000 R13: 00007fc6b39d6038 R14: 00007fc6b39d5fa0 R15: 00007ffc86986fd8 GRED: Unable to relocate VQ 0x0 after dequeue, screwing up backlog GRED: Unable to relocate VQ 0x0 after dequeue, screwing up backlog GRED: Unable to relocate VQ 0x0 after dequeue, screwing up backlog GRED: Unable to relocate VQ 0x0 after dequeue, screwing up backlog GRED: Unable to relocate VQ 0x0 after dequeue, screwing up backlog GRED: Unable to relocate VQ 0x0 after dequeue, screwing up backlog GRED: Unable to relocate VQ 0x0 after dequeue, screwing up backlog GRED: Unable to relocate VQ 0x0 after dequeue, screwing up backlog GRED: Unable to relocate VQ 0x0 after dequeue, screwing up backlog GRED: Unable to relocate VQ 0x0 after dequeue, screwing up backlog