======================================================
WARNING: possible circular locking dependency detected
6.15.0-rc7-syzkaller #0 Not tainted
------------------------------------------------------
syz.4.9165/30420 is trying to acquire lock:
ffffffff9037a878 (nr_neigh_list_lock){+...}-{3:3}, at: spin_lock_bh include/linux/spinlock.h:356 [inline]
ffffffff9037a878 (nr_neigh_list_lock){+...}-{3:3}, at: nr_remove_neigh+0x1a/0x290 net/netrom/nr_route.c:307

but task is already holding lock:
ffff888028f8b470 (&nr_node->node_lock){+...}-{3:3}, at: spin_lock_bh include/linux/spinlock.h:356 [inline]
ffff888028f8b470 (&nr_node->node_lock){+...}-{3:3}, at: nr_node_lock include/net/netrom.h:152 [inline]
ffff888028f8b470 (&nr_node->node_lock){+...}-{3:3}, at: nr_add_node+0x60b/0x2c00 net/netrom/nr_route.c:214

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #2 (&nr_node->node_lock){+...}-{3:3}:
       __raw_spin_lock_bh include/linux/spinlock_api_smp.h:126 [inline]
       _raw_spin_lock_bh+0x33/0x40 kernel/locking/spinlock.c:178
       spin_lock_bh include/linux/spinlock.h:356 [inline]
       nr_node_lock include/net/netrom.h:152 [inline]
       nr_rt_device_down+0x18e/0x810 net/netrom/nr_route.c:519
       nr_device_event+0x126/0x170 net/netrom/af_netrom.c:126
       notifier_call_chain+0xbc/0x410 kernel/notifier.c:85
       call_netdevice_notifiers_info+0xbe/0x140 net/core/dev.c:2176
       call_netdevice_notifiers_extack net/core/dev.c:2214 [inline]
       call_netdevice_notifiers net/core/dev.c:2228 [inline]
       __dev_notify_flags+0x1f7/0x2e0 net/core/dev.c:9395
       netif_change_flags+0x108/0x160 net/core/dev.c:9422
       dev_change_flags+0xba/0x250 net/core/dev_api.c:68
       dev_ifsioc+0x1498/0x1f70 net/core/dev_ioctl.c:565
       dev_ioctl+0x223/0x10e0 net/core/dev_ioctl.c:821
       sock_do_ioctl+0x19d/0x280 net/socket.c:1204
       sock_ioctl+0x227/0x6b0 net/socket.c:1311
       vfs_ioctl fs/ioctl.c:51 [inline]
       __do_sys_ioctl fs/ioctl.c:906 [inline]
       __se_sys_ioctl fs/ioctl.c:892 [inline]
       __x64_sys_ioctl+0x190/0x200 fs/ioctl.c:892
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xcd/0x260 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #1 (nr_node_list_lock){+...}-{3:3}:
       __raw_spin_lock_bh include/linux/spinlock_api_smp.h:126 [inline]
       _raw_spin_lock_bh+0x33/0x40 kernel/locking/spinlock.c:178
       spin_lock_bh include/linux/spinlock.h:356 [inline]
       nr_rt_device_down+0xd3/0x810 net/netrom/nr_route.c:517
       nr_device_event+0x126/0x170 net/netrom/af_netrom.c:126
       notifier_call_chain+0xbc/0x410 kernel/notifier.c:85
       call_netdevice_notifiers_info+0xbe/0x140 net/core/dev.c:2176
       call_netdevice_notifiers_extack net/core/dev.c:2214 [inline]
       call_netdevice_notifiers net/core/dev.c:2228 [inline]
       __dev_notify_flags+0x1f7/0x2e0 net/core/dev.c:9395
       netif_change_flags+0x108/0x160 net/core/dev.c:9422
       dev_change_flags+0xba/0x250 net/core/dev_api.c:68
       dev_ifsioc+0x1498/0x1f70 net/core/dev_ioctl.c:565
       dev_ioctl+0x223/0x10e0 net/core/dev_ioctl.c:821
       sock_do_ioctl+0x19d/0x280 net/socket.c:1204
       sock_ioctl+0x227/0x6b0 net/socket.c:1311
       vfs_ioctl fs/ioctl.c:51 [inline]
       __do_sys_ioctl fs/ioctl.c:906 [inline]
       __se_sys_ioctl fs/ioctl.c:892 [inline]
       __x64_sys_ioctl+0x190/0x200 fs/ioctl.c:892
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xcd/0x260 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #0 (nr_neigh_list_lock){+...}-{3:3}:
       check_prev_add kernel/locking/lockdep.c:3166 [inline]
       check_prevs_add kernel/locking/lockdep.c:3285 [inline]
       validate_chain kernel/locking/lockdep.c:3909 [inline]
       __lock_acquire+0x1173/0x1ba0 kernel/locking/lockdep.c:5235
       lock_acquire kernel/locking/lockdep.c:5866 [inline]
       lock_acquire+0x179/0x350 kernel/locking/lockdep.c:5823
       __raw_spin_lock_bh include/linux/spinlock_api_smp.h:126 [inline]
       _raw_spin_lock_bh+0x33/0x40 kernel/locking/spinlock.c:178
       spin_lock_bh include/linux/spinlock.h:356 [inline]
       nr_remove_neigh+0x1a/0x290 net/netrom/nr_route.c:307
       nr_add_node+0x2408/0x2c00 net/netrom/nr_route.c:249
       nr_rt_ioctl+0x11b7/0x29b0 net/netrom/nr_route.c:651
       nr_ioctl+0x19a/0x2e0 net/netrom/af_netrom.c:1254
       sock_do_ioctl+0x115/0x280 net/socket.c:1190
       sock_ioctl+0x227/0x6b0 net/socket.c:1311
       vfs_ioctl fs/ioctl.c:51 [inline]
       __do_sys_ioctl fs/ioctl.c:906 [inline]
       __se_sys_ioctl fs/ioctl.c:892 [inline]
       __x64_sys_ioctl+0x190/0x200 fs/ioctl.c:892
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xcd/0x260 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_neigh_list_lock --> nr_node_list_lock --> &nr_node->node_lock

 Possible unsafe locking scenario:

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

 *** DEADLOCK ***

1 lock held by syz.4.9165/30420:
 #0: ffff888028f8b470 (&nr_node->node_lock){+...}-{3:3}, at: spin_lock_bh include/linux/spinlock.h:356 [inline]
 #0: ffff888028f8b470 (&nr_node->node_lock){+...}-{3:3}, at: nr_node_lock include/net/netrom.h:152 [inline]
 #0: ffff888028f8b470 (&nr_node->node_lock){+...}-{3:3}, at: nr_add_node+0x60b/0x2c00 net/netrom/nr_route.c:214

stack backtrace:
CPU: 2 UID: 0 PID: 30420 Comm: syz.4.9165 Not tainted 6.15.0-rc7-syzkaller #0 PREEMPT(full) 
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:94 [inline]
 dump_stack_lvl+0x116/0x1f0 lib/dump_stack.c:120
 print_circular_bug+0x275/0x350 kernel/locking/lockdep.c:2079
 check_noncircular+0x14c/0x170 kernel/locking/lockdep.c:2211
 check_prev_add kernel/locking/lockdep.c:3166 [inline]
 check_prevs_add kernel/locking/lockdep.c:3285 [inline]
 validate_chain kernel/locking/lockdep.c:3909 [inline]
 __lock_acquire+0x1173/0x1ba0 kernel/locking/lockdep.c:5235
 lock_acquire kernel/locking/lockdep.c:5866 [inline]
 lock_acquire+0x179/0x350 kernel/locking/lockdep.c:5823
 __raw_spin_lock_bh include/linux/spinlock_api_smp.h:126 [inline]
 _raw_spin_lock_bh+0x33/0x40 kernel/locking/spinlock.c:178
 spin_lock_bh include/linux/spinlock.h:356 [inline]
 nr_remove_neigh+0x1a/0x290 net/netrom/nr_route.c:307
 nr_add_node+0x2408/0x2c00 net/netrom/nr_route.c:249
 nr_rt_ioctl+0x11b7/0x29b0 net/netrom/nr_route.c:651
 nr_ioctl+0x19a/0x2e0 net/netrom/af_netrom.c:1254
 sock_do_ioctl+0x115/0x280 net/socket.c:1190
 sock_ioctl+0x227/0x6b0 net/socket.c:1311
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:906 [inline]
 __se_sys_ioctl fs/ioctl.c:892 [inline]
 __x64_sys_ioctl+0x190/0x200 fs/ioctl.c:892
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xcd/0x260 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f0c5218e969
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:00007f0c4fff6038 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007f0c523b5fa0 RCX: 00007f0c5218e969
RDX: 0000200000000280 RSI: 000000000000890b RDI: 0000000000000004
RBP: 00007f0c52210ab1 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 0000000000000000 R14: 00007f0c523b5fa0 R15: 00007fff7ec618b8
 </TASK>