======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
syz.0.6411/28425 is trying to acquire lock:
ffffffff8f426ab8 (nr_node_list_lock){+...}-{3:3}, at: spin_lock_bh include/linux/spinlock.h:356 [inline]
ffffffff8f426ab8 (nr_node_list_lock){+...}-{3:3}, at: nr_rt_device_down+0xa9/0x720 net/netrom/nr_route.c:517

but task is already holding lock:
ffffffff8f426a58 (nr_neigh_list_lock){+...}-{3:3}, at: spin_lock_bh include/linux/spinlock.h:356 [inline]
ffffffff8f426a58 (nr_neigh_list_lock){+...}-{3:3}, at: nr_rt_device_down+0x28/0x720 net/netrom/nr_route.c:514

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #2 (nr_neigh_list_lock){+...}-{3:3}:
       lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5868
       __raw_spin_lock_bh include/linux/spinlock_api_smp.h:126 [inline]
       _raw_spin_lock_bh+0x36/0x50 kernel/locking/spinlock.c:178
       spin_lock_bh include/linux/spinlock.h:356 [inline]
       nr_remove_neigh net/netrom/nr_route.c:307 [inline]
       nr_dec_obs net/netrom/nr_route.c:472 [inline]
       nr_rt_ioctl+0x390/0xd50 net/netrom/nr_route.c:692
       sock_do_ioctl+0xdc/0x300 net/socket.c:1254
       sock_ioctl+0x576/0x790 net/socket.c:1375
       vfs_ioctl fs/ioctl.c:51 [inline]
       __do_sys_ioctl fs/ioctl.c:597 [inline]
       __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:583
       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

-> #1 (&nr_node->node_lock){+...}-{3:3}:
       lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5868
       __raw_spin_lock_bh include/linux/spinlock_api_smp.h:126 [inline]
       _raw_spin_lock_bh+0x36/0x50 kernel/locking/spinlock.c:178
       spin_lock_bh include/linux/spinlock.h:356 [inline]
       nr_node_lock include/net/netrom.h:152 [inline]
       nr_dec_obs net/netrom/nr_route.c:459 [inline]
       nr_rt_ioctl+0x193/0xd50 net/netrom/nr_route.c:692
       sock_do_ioctl+0xdc/0x300 net/socket.c:1254
       sock_ioctl+0x576/0x790 net/socket.c:1375
       vfs_ioctl fs/ioctl.c:51 [inline]
       __do_sys_ioctl fs/ioctl.c:597 [inline]
       __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:583
       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

-> #0 (nr_node_list_lock){+...}-{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_bh include/linux/spinlock_api_smp.h:126 [inline]
       _raw_spin_lock_bh+0x36/0x50 kernel/locking/spinlock.c:178
       spin_lock_bh include/linux/spinlock.h:356 [inline]
       nr_rt_device_down+0xa9/0x720 net/netrom/nr_route.c:517
       nr_device_event+0x137/0x150 net/netrom/af_netrom.c:126
       notifier_call_chain+0x1b6/0x3e0 kernel/notifier.c:85
       call_netdevice_notifiers_extack net/core/dev.c:2267 [inline]
       call_netdevice_notifiers net/core/dev.c:2281 [inline]
       __dev_notify_flags+0x18d/0x2e0 net/core/dev.c:-1
       netif_change_flags+0xe8/0x1a0 net/core/dev.c:9705
       dev_change_flags+0x130/0x260 net/core/dev_api.c:68
       dev_ioctl+0x7b4/0x1150 net/core/dev_ioctl.c:841
       sock_do_ioctl+0x22c/0x300 net/socket.c:1268
       sock_ioctl+0x576/0x790 net/socket.c:1375
       vfs_ioctl fs/ioctl.c:51 [inline]
       __do_sys_ioctl fs/ioctl.c:597 [inline]
       __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:583
       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:

Chain exists of:
  nr_node_list_lock --> &nr_node->node_lock --> nr_neigh_list_lock

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(nr_neigh_list_lock);
                               lock(&nr_node->node_lock);
                               lock(nr_neigh_list_lock);
  lock(nr_node_list_lock);

 *** DEADLOCK ***

2 locks held by syz.0.6411/28425:
 #0: ffffffff8f2cbd88 (rtnl_mutex){+.+.}-{4:4}, at: rtnl_net_lock include/linux/rtnetlink.h:130 [inline]
 #0: ffffffff8f2cbd88 (rtnl_mutex){+.+.}-{4:4}, at: dev_ioctl+0x7a4/0x1150 net/core/dev_ioctl.c:840
 #1: ffffffff8f426a58 (nr_neigh_list_lock){+...}-{3:3}, at: spin_lock_bh include/linux/spinlock.h:356 [inline]
 #1: ffffffff8f426a58 (nr_neigh_list_lock){+...}-{3:3}, at: nr_rt_device_down+0x28/0x720 net/netrom/nr_route.c:514

stack backtrace:
CPU: 1 UID: 0 PID: 28425 Comm: syz.0.6411 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
Call Trace:
 <TASK>
 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_bh include/linux/spinlock_api_smp.h:126 [inline]
 _raw_spin_lock_bh+0x36/0x50 kernel/locking/spinlock.c:178
 spin_lock_bh include/linux/spinlock.h:356 [inline]
 nr_rt_device_down+0xa9/0x720 net/netrom/nr_route.c:517
 nr_device_event+0x137/0x150 net/netrom/af_netrom.c:126
 notifier_call_chain+0x1b6/0x3e0 kernel/notifier.c:85
 call_netdevice_notifiers_extack net/core/dev.c:2267 [inline]
 call_netdevice_notifiers net/core/dev.c:2281 [inline]
 __dev_notify_flags+0x18d/0x2e0 net/core/dev.c:-1
 netif_change_flags+0xe8/0x1a0 net/core/dev.c:9705
 dev_change_flags+0x130/0x260 net/core/dev_api.c:68
 dev_ioctl+0x7b4/0x1150 net/core/dev_ioctl.c:841
 sock_do_ioctl+0x22c/0x300 net/socket.c:1268
 sock_ioctl+0x576/0x790 net/socket.c:1375
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:597 [inline]
 __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:583
 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: 0033:0x7fc22af8f749
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:00007fc22bd56038 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007fc22b1e5fa0 RCX: 00007fc22af8f749
RDX: 0000200000000000 RSI: 0000000000008914 RDI: 000000000000000b
RBP: 00007fc22b013f91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fc22b1e6038 R14: 00007fc22b1e5fa0 R15: 00007ffd2cc42da8
 </TASK>
warn_alloc: 1 callbacks suppressed
syz.0.6411: vmalloc error: size 6291456, failed to allocated page array size 12288, mode:0xdc2(GFP_KERNEL|__GFP_HIGHMEM|__GFP_ZERO), nodemask=(null),cpuset=/,mems_allowed=0-1
CPU: 0 UID: 0 PID: 28425 Comm: syz.0.6411 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
Call Trace:
 <TASK>
 dump_stack_lvl+0x189/0x250 lib/dump_stack.c:120
 warn_alloc+0x214/0x310 mm/page_alloc.c:3962
 __vmalloc_area_node mm/vmalloc.c:3706 [inline]
 __vmalloc_node_range_noprof+0x690/0x12d0 mm/vmalloc.c:3897
 __kvmalloc_node_noprof+0x674/0x910 mm/slub.c:7134
 kvmalloc_array_node_noprof include/linux/slab.h:1122 [inline]
 fq_pie_init+0x435/0x840 net/sched/sch_fq_pie.c:451
 qdisc_create+0x7ac/0xea0 net/sched/sch_api.c:1319
 __tc_modify_qdisc net/sched/sch_api.c:1753 [inline]
 tc_modify_qdisc+0x1547/0x2020 net/sched/sch_api.c:1817
 rtnetlink_rcv_msg+0x77c/0xb70 net/core/rtnetlink.c:6960
 netlink_rcv_skb+0x208/0x470 net/netlink/af_netlink.c:2552
 netlink_unicast_kernel net/netlink/af_netlink.c:1320 [inline]
 netlink_unicast+0x82f/0x9e0 net/netlink/af_netlink.c:1346
 netlink_sendmsg+0x805/0xb30 net/netlink/af_netlink.c:1896
 sock_sendmsg_nosec net/socket.c:727 [inline]
 __sock_sendmsg+0x21c/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: 0033:0x7fc22af8f749
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:00007fc22bd56038 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
RAX: ffffffffffffffda RBX: 00007fc22b1e5fa0 RCX: 00007fc22af8f749
RDX: 000000002000400c RSI: 0000200000000300 RDI: 000000000000000d
RBP: 00007fc22b013f91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fc22b1e6038 R14: 00007fc22b1e5fa0 R15: 00007ffd2cc42da8
 </TASK>
Mem-Info:
active_anon:1863 inactive_anon:0 isolated_anon:0
 active_file:3079 inactive_file:40090 isolated_file:0
 unevictable:768 dirty:57 writeback:0
 slab_reclaimable:14353 slab_unreclaimable:170525
 mapped:12360 shmem:1366 pagetables:921
 sec_pagetables:0 bounce:0
 kernel_misc_reclaimable:0
 free:1276043 free_pcp:16673 free_cma:0
Node 0 active_anon:7392kB inactive_anon:0kB active_file:12316kB inactive_file:160160kB unevictable:1536kB isolated(anon):0kB isolated(file):0kB mapped:49348kB dirty:228kB writeback:0kB shmem:3928kB shmem_thp:0kB shmem_pmdmapped:0kB anon_thp:0kB kernel_stack:18032kB pagetables:3492kB sec_pagetables:0kB all_unreclaimable? no Balloon:0kB
Node 1 active_anon:0kB inactive_anon:0kB active_file:0kB inactive_file:200kB unevictable:1536kB isolated(anon):0kB isolated(file):0kB mapped:0kB dirty:0kB writeback:0kB shmem:1536kB shmem_thp:0kB shmem_pmdmapped:0kB anon_thp:0kB kernel_stack:48kB pagetables:148kB sec_pagetables:0kB all_unreclaimable? no Balloon:0kB
Node 0 DMA free:15360kB boost:0kB min:204kB low:252kB high:300kB reserved_highatomic:0KB free_highatomic:0KB active_anon:0kB inactive_anon:0kB active_file:0kB inactive_file:0kB unevictable:0kB writepending:0kB zspages:0kB present:15992kB managed:15360kB mlocked:0kB bounce:0kB free_pcp:0kB local_pcp:0kB free_cma:0kB
lowmem_reserve[]: 0 2505 2505 2505 2505
Node 0 DMA32 free:1200872kB boost:0kB min:34308kB low:42884kB high:51460kB reserved_highatomic:0KB free_highatomic:0KB active_anon:7392kB inactive_anon:0kB active_file:12316kB inactive_file:160160kB unevictable:1536kB writepending:228kB zspages:0kB present:3129332kB managed:2565152kB mlocked:0kB bounce:0kB free_pcp:44824kB local_pcp:19880kB free_cma:0kB
lowmem_reserve[]: 0 0 0 0 0
Node 0 Normal free:0kB boost:0kB min:0kB low:0kB high:0kB reserved_highatomic:0KB free_highatomic:0KB active_anon:0kB inactive_anon:0kB active_file:0kB inactive_file:0kB unevictable:0kB writepending:0kB zspages:0kB present:1048580kB managed:108kB mlocked:0kB bounce:0kB free_pcp:0kB local_pcp:0kB free_cma:0kB
lowmem_reserve[]: 0 0 0 0 0
Node 1 Normal free:3897112kB boost:0kB min:55592kB low:69488kB high:83384kB reserved_highatomic:0KB free_highatomic:0KB active_anon:0kB inactive_anon:0kB active_file:0kB inactive_file:200kB unevictable:1536kB writepending:0kB zspages:0kB present:4194300kB managed:4111100kB mlocked:0kB bounce:0kB free_pcp:19924kB local_pcp:13484kB free_cma:0kB
lowmem_reserve[]: 0 0 0 0 0
Node 0 DMA: 0*4kB 0*8kB 0*16kB 0*32kB 0*64kB 0*128kB 0*256kB 0*512kB 1*1024kB (U) 1*2048kB (M) 3*4096kB (M) = 15360kB
Node 0 DMA32: 5219*4kB (UME) 1566*8kB (UME) 803*16kB (UM) 1001*32kB (UME) 636*64kB (UM) 839*128kB (UM) 624*256kB (UME) 363*512kB (UE) 212*1024kB (UM) 3*2048kB (UM) 99*4096kB (UM) = 1200716kB
Node 0 Normal: 0*4kB 0*8kB 0*16kB 0*32kB 0*64kB 0*128kB 0*256kB 0*512kB 0*1024kB 0*2048kB 0*4096kB = 0kB
Node 1 Normal: 2*4kB (E) 8*8kB (UME) 9*16kB (UME) 6*32kB (ME) 32*64kB (UME) 9*128kB (UME) 5*256kB (UME) 4*512kB (UME) 3*1024kB (UME) 2*2048kB (UE) 948*4096kB (M) = 3897112kB
Node 0 hugepages_total=0 hugepages_free=0 hugepages_surp=0 hugepages_size=1048576kB
Node 0 hugepages_total=2 hugepages_free=2 hugepages_surp=0 hugepages_size=2048kB
Node 1 hugepages_total=0 hugepages_free=0 hugepages_surp=0 hugepages_size=1048576kB
Node 1 hugepages_total=2 hugepages_free=2 hugepages_surp=0 hugepages_size=2048kB
44534 total pagecache pages
0 pages in swap cache
Free swap  = 124996kB
Total swap = 124996kB
2097051 pages RAM
0 pages HighMem/MovableOnly
424121 pages reserved
0 pages cma reserved