GRED: Unable to relocate VQ 0x0 after dequeue, screwing up backlog ====================================================== WARNING: possible circular locking dependency detected syzkaller #0 Not tainted ------------------------------------------------------ syz.2.629/8039 is trying to acquire lock: ffff88807c3c2218 (dev->qdisc_tx_busylock ?: &qdisc_tx_busylock#3){+...}-{3:3}, at: spin_lock include/linux/spinlock.h:351 [inline] ffff88807c3c2218 (dev->qdisc_tx_busylock ?: &qdisc_tx_busylock#3){+...}-{3:3}, at: __dev_xmit_skb net/core/dev.c:4186 [inline] ffff88807c3c2218 (dev->qdisc_tx_busylock ?: &qdisc_tx_busylock#3){+...}-{3:3}, at: __dev_queue_xmit+0x22b7/0x3b50 net/core/dev.c:4729 but task is already holding lock: ffff888022302d58 (&qdisc_xmit_lock_key#4){+.-.}-{3:3}, at: spin_lock include/linux/spinlock.h:351 [inline] ffff888022302d58 (&qdisc_xmit_lock_key#4){+.-.}-{3:3}, at: __netif_tx_lock include/linux/netdevice.h:4685 [inline] ffff888022302d58 (&qdisc_xmit_lock_key#4){+.-.}-{3:3}, at: sch_direct_xmit+0x153/0x4b0 net/sched/sch_generic.c:345 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:4685 [inline] sch_direct_xmit+0x153/0x4b0 net/sched/sch_generic.c:345 __dev_xmit_skb net/core/dev.c:4152 [inline] __dev_queue_xmit+0x1857/0x3b50 net/core/dev.c:4729 neigh_output include/net/neighbour.h:547 [inline] ip6_finish_output2+0xfb3/0x1480 net/ipv6/ip6_output.c:136 NF_HOOK_COND include/linux/netfilter.h:307 [inline] ip6_output+0x340/0x550 net/ipv6/ip6_output.c:247 NF_HOOK+0x9e/0x380 include/linux/netfilter.h:318 mld_sendpack+0x8d4/0xe60 net/ipv6/mcast.c:1855 mld_send_cr net/ipv6/mcast.c:2154 [inline] mld_ifc_work+0x83e/0xd60 net/ipv6/mcast.c:2693 process_one_work kernel/workqueue.c:3263 [inline] process_scheduled_works+0xae1/0x17b0 kernel/workqueue.c:3346 worker_thread+0x8a0/0xda0 kernel/workqueue.c:3427 kthread+0x711/0x8a0 kernel/kthread.c:463 ret_from_fork+0x4bc/0x870 arch/x86/kernel/process.c:158 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:4186 [inline] __dev_queue_xmit+0x22b7/0x3b50 net/core/dev.c:4729 neigh_output include/net/neighbour.h:547 [inline] ip6_finish_output2+0xfb3/0x1480 net/ipv6/ip6_output.c:136 NF_HOOK_COND include/linux/netfilter.h:307 [inline] ip6_output+0x340/0x550 net/ipv6/ip6_output.c:247 NF_HOOK include/linux/netfilter.h:318 [inline] ndisc_send_skb+0xbce/0x1510 net/ipv6/ndisc.c:512 ndisc_send_ns net/ipv6/ndisc.c:670 [inline] ndisc_solicit+0x444/0x610 net/ipv6/ndisc.c:-1 neigh_probe net/core/neighbour.c:1098 [inline] __neigh_event_send+0xf70/0x1560 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] ip6_finish_output2+0xfb3/0x1480 net/ipv6/ip6_output.c:136 NF_HOOK_COND include/linux/netfilter.h:307 [inline] ip6_output+0x340/0x550 net/ipv6/ip6_output.c:247 ip6_send_skb+0x1d5/0x390 net/ipv6/ip6_output.c:1994 icmp6_send+0x12c6/0x1940 net/ipv6/icmp.c:633 __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:851 __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:5248 [inline] netdev_start_xmit include/linux/netdevice.h:5257 [inline] xmit_one net/core/dev.c:3845 [inline] dev_hard_start_xmit+0x2d7/0x830 net/core/dev.c:3861 sch_direct_xmit+0x241/0x4b0 net/sched/sch_generic.c:347 qdisc_restart net/sched/sch_generic.c:412 [inline] __qdisc_run+0xaa0/0x1540 net/sched/sch_generic.c:420 __dev_xmit_skb net/core/dev.c:4221 [inline] __dev_queue_xmit+0x1056/0x3b50 net/core/dev.c:4729 neigh_output include/net/neighbour.h:547 [inline] ip6_finish_output2+0xfb3/0x1480 net/ipv6/ip6_output.c:136 NF_HOOK_COND include/linux/netfilter.h:307 [inline] ip6_output+0x340/0x550 net/ipv6/ip6_output.c:247 ip6_mr_output+0x4e9/0x1100 net/ipv6/ip6mr.c:2415 NF_HOOK include/linux/netfilter.h:318 [inline] rawv6_send_hdrinc+0xe16/0x17a0 net/ipv6/raw.c:661 rawv6_sendmsg+0x12ee/0x1830 net/ipv6/raw.c:906 sock_sendmsg_nosec net/socket.c:727 [inline] __sock_sendmsg+0x19c/0x270 net/socket.c:742 ____sys_sendmsg+0x505/0x830 net/socket.c:2630 ___sys_sendmsg+0x21f/0x2a0 net/socket.c:2684 __sys_sendmsg net/socket.c:2716 [inline] __do_sys_sendmsg net/socket.c:2721 [inline] __se_sys_sendmsg net/socket.c:2719 [inline] __x64_sys_sendmsg+0x19b/0x260 net/socket.c:2719 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline] do_syscall_64+0xfa/0xfa0 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 *** 12 locks held by syz.2.629/8039: #0: ffffffff8df3d660 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:331 [inline] #0: ffffffff8df3d660 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:867 [inline] #0: ffffffff8df3d660 (rcu_read_lock){....}-{1:3}, at: rawv6_send_hdrinc+0xc9f/0x17a0 net/ipv6/raw.c:659 #1: ffffffff8df3d660 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:331 [inline] #1: ffffffff8df3d660 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:867 [inline] #1: ffffffff8df3d660 (rcu_read_lock){....}-{1:3}, at: class_rcu_constructor include/linux/rcupdate.h:1195 [inline] #1: ffffffff8df3d660 (rcu_read_lock){....}-{1:3}, at: ip6_mr_output+0x1ca/0x1100 net/ipv6/ip6mr.c:2375 #2: ffffffff8df3d660 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:331 [inline] #2: ffffffff8df3d660 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:867 [inline] #2: ffffffff8df3d660 (rcu_read_lock){....}-{1:3}, at: ip6_output+0x126/0x550 net/ipv6/ip6_output.c:235 #3: ffffffff8df3d6c0 (rcu_read_lock_bh){....}-{1:3}, at: local_bh_disable include/linux/bottom_half.h:20 [inline] #3: ffffffff8df3d6c0 (rcu_read_lock_bh){....}-{1:3}, at: rcu_read_lock_bh include/linux/rcupdate.h:918 [inline] #3: ffffffff8df3d6c0 (rcu_read_lock_bh){....}-{1:3}, at: __dev_queue_xmit+0x27b/0x3b50 net/core/dev.c:4688 #4: ffff888022302d58 (&qdisc_xmit_lock_key#4){+.-.}-{3:3}, at: spin_lock include/linux/spinlock.h:351 [inline] #4: ffff888022302d58 (&qdisc_xmit_lock_key#4){+.-.}-{3:3}, at: __netif_tx_lock include/linux/netdevice.h:4685 [inline] #4: ffff888022302d58 (&qdisc_xmit_lock_key#4){+.-.}-{3:3}, at: sch_direct_xmit+0x153/0x4b0 net/sched/sch_generic.c:345 #5: ffffffff8df3d660 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:331 [inline] #5: ffffffff8df3d660 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:867 [inline] #5: ffffffff8df3d660 (rcu_read_lock){....}-{1:3}, at: icmp6_send+0x1e9/0x1940 net/ipv6/icmp.c:478 #6: ffff88802f940a20 (k-slock-AF_INET6){+.-.}-{3:3}, at: spin_trylock include/linux/spinlock.h:361 [inline] #6: ffff88802f940a20 (k-slock-AF_INET6){+.-.}-{3:3}, at: icmpv6_xmit_lock net/ipv6/icmp.c:108 [inline] #6: ffff88802f940a20 (k-slock-AF_INET6){+.-.}-{3:3}, at: icmp6_send+0xc5c/0x1940 net/ipv6/icmp.c:555 #7: ffffffff8df3d660 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:331 [inline] #7: ffffffff8df3d660 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:867 [inline] #7: ffffffff8df3d660 (rcu_read_lock){....}-{1:3}, at: ip6_send_skb+0x10f/0x390 net/ipv6/ip6_output.c:1993 #8: ffffffff8df3d660 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:331 [inline] #8: ffffffff8df3d660 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:867 [inline] #8: ffffffff8df3d660 (rcu_read_lock){....}-{1:3}, at: ip6_output+0x126/0x550 net/ipv6/ip6_output.c:235 #9: ffffffff8df3d660 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:331 [inline] #9: ffffffff8df3d660 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:867 [inline] #9: ffffffff8df3d660 (rcu_read_lock){....}-{1:3}, at: ndisc_send_skb+0x1e4/0x1510 net/ipv6/ndisc.c:482 #10: ffffffff8df3d660 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:331 [inline] #10: ffffffff8df3d660 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:867 [inline] #10: ffffffff8df3d660 (rcu_read_lock){....}-{1:3}, at: ip6_output+0x126/0x550 net/ipv6/ip6_output.c:235 #11: ffffffff8df3d6c0 (rcu_read_lock_bh){....}-{1:3}, at: local_bh_disable include/linux/bottom_half.h:20 [inline] #11: ffffffff8df3d6c0 (rcu_read_lock_bh){....}-{1:3}, at: rcu_read_lock_bh include/linux/rcupdate.h:918 [inline] #11: ffffffff8df3d6c0 (rcu_read_lock_bh){....}-{1:3}, at: __dev_queue_xmit+0x27b/0x3b50 net/core/dev.c:4688 stack backtrace: CPU: 1 UID: 0 PID: 8039 Comm: syz.2.629 Not tainted syzkaller #0 PREEMPT(full) Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025 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:4186 [inline] __dev_queue_xmit+0x22b7/0x3b50 net/core/dev.c:4729 neigh_output include/net/neighbour.h:547 [inline] ip6_finish_output2+0xfb3/0x1480 net/ipv6/ip6_output.c:136 NF_HOOK_COND include/linux/netfilter.h:307 [inline] ip6_output+0x340/0x550 net/ipv6/ip6_output.c:247 NF_HOOK include/linux/netfilter.h:318 [inline] ndisc_send_skb+0xbce/0x1510 net/ipv6/ndisc.c:512 ndisc_send_ns net/ipv6/ndisc.c:670 [inline] ndisc_solicit+0x444/0x610 net/ipv6/ndisc.c:-1 neigh_probe net/core/neighbour.c:1098 [inline] __neigh_event_send+0xf70/0x1560 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] ip6_finish_output2+0xfb3/0x1480 net/ipv6/ip6_output.c:136 NF_HOOK_COND include/linux/netfilter.h:307 [inline] ip6_output+0x340/0x550 net/ipv6/ip6_output.c:247 ip6_send_skb+0x1d5/0x390 net/ipv6/ip6_output.c:1994 icmp6_send+0x12c6/0x1940 net/ipv6/icmp.c:633 __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:851 __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:5248 [inline] netdev_start_xmit include/linux/netdevice.h:5257 [inline] xmit_one net/core/dev.c:3845 [inline] dev_hard_start_xmit+0x2d7/0x830 net/core/dev.c:3861 sch_direct_xmit+0x241/0x4b0 net/sched/sch_generic.c:347 qdisc_restart net/sched/sch_generic.c:412 [inline] __qdisc_run+0xaa0/0x1540 net/sched/sch_generic.c:420 __dev_xmit_skb net/core/dev.c:4221 [inline] __dev_queue_xmit+0x1056/0x3b50 net/core/dev.c:4729 neigh_output include/net/neighbour.h:547 [inline] ip6_finish_output2+0xfb3/0x1480 net/ipv6/ip6_output.c:136 NF_HOOK_COND include/linux/netfilter.h:307 [inline] ip6_output+0x340/0x550 net/ipv6/ip6_output.c:247 ip6_mr_output+0x4e9/0x1100 net/ipv6/ip6mr.c:2415 NF_HOOK include/linux/netfilter.h:318 [inline] rawv6_send_hdrinc+0xe16/0x17a0 net/ipv6/raw.c:661 rawv6_sendmsg+0x12ee/0x1830 net/ipv6/raw.c:906 sock_sendmsg_nosec net/socket.c:727 [inline] __sock_sendmsg+0x19c/0x270 net/socket.c:742 ____sys_sendmsg+0x505/0x830 net/socket.c:2630 ___sys_sendmsg+0x21f/0x2a0 net/socket.c:2684 __sys_sendmsg net/socket.c:2716 [inline] __do_sys_sendmsg net/socket.c:2721 [inline] __se_sys_sendmsg net/socket.c:2719 [inline] __x64_sys_sendmsg+0x19b/0x260 net/socket.c:2719 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline] do_syscall_64+0xfa/0xfa0 arch/x86/entry/syscall_64.c:94 entry_SYSCALL_64_after_hwframe+0x77/0x7f RIP: 0033:0x7f05a918f6c9 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:00007f05aa076038 EFLAGS: 00000246 ORIG_RAX: 000000000000002e RAX: ffffffffffffffda RBX: 00007f05a93e6090 RCX: 00007f05a918f6c9 RDX: 0000000000000000 RSI: 0000200000000000 RDI: 000000000000000c RBP: 00007f05a9211f91 R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000 R13: 00007f05a93e6128 R14: 00007f05a93e6090 R15: 00007ffcb166c238 GRED: Unable to relocate VQ 0x0 after dequeue, screwing up backlog