syzbot

======================================================
WARNING: possible circular locking dependency detected
6.1.123-syzkaller #0 Not tainted
------------------------------------------------------
syz.3.46/4536 is trying to acquire lock:
ffffffff8e653298 (nr_node_list_lock){+...}-{2:2}, at: spin_lock_bh include/linux/spinlock.h:356 [inline]
ffffffff8e653298 (nr_node_list_lock){+...}-{2:2}, at: nr_rt_device_down+0xb1/0x7b0 net/netrom/nr_route.c:517

but task is already holding lock:
ffffffff8e653238 (nr_neigh_list_lock){+...}-{2:2}, at: spin_lock_bh include/linux/spinlock.h:356 [inline]
ffffffff8e653238 (nr_neigh_list_lock){+...}-{2:2}, at: nr_rt_device_down+0x24/0x7b0 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){+...}-{2:2}:
       lock_acquire+0x1f8/0x5a0 kernel/locking/lockdep.c:5662
       __raw_spin_lock_bh include/linux/spinlock_api_smp.h:126 [inline]
       _raw_spin_lock_bh+0x31/0x40 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+0x394/0xfb0 net/netrom/nr_route.c:692
       sock_do_ioctl+0x152/0x450 net/socket.c:1204
       sock_ioctl+0x47f/0x770 net/socket.c:1321
       vfs_ioctl fs/ioctl.c:51 [inline]
       __do_sys_ioctl fs/ioctl.c:870 [inline]
       __se_sys_ioctl+0xf1/0x160 fs/ioctl.c:856
       do_syscall_x64 arch/x86/entry/common.c:51 [inline]
       do_syscall_64+0x3b/0xb0 arch/x86/entry/common.c:81
       entry_SYSCALL_64_after_hwframe+0x68/0xd2

-> #1 (&nr_node->node_lock){+...}-{2:2}:
       lock_acquire+0x1f8/0x5a0 kernel/locking/lockdep.c:5662
       __raw_spin_lock_bh include/linux/spinlock_api_smp.h:126 [inline]
       _raw_spin_lock_bh+0x31/0x40 kernel/locking/spinlock.c:178
       spin_lock_bh include/linux/spinlock.h:356 [inline]
       nr_node_lock include/net/netrom.h:152 [inline]
       nr_dec_obs net/netrom/nr_route.c:459 [inline]
       nr_rt_ioctl+0x18e/0xfb0 net/netrom/nr_route.c:692
       sock_do_ioctl+0x152/0x450 net/socket.c:1204
       sock_ioctl+0x47f/0x770 net/socket.c:1321
       vfs_ioctl fs/ioctl.c:51 [inline]
       __do_sys_ioctl fs/ioctl.c:870 [inline]
       __se_sys_ioctl+0xf1/0x160 fs/ioctl.c:856
       do_syscall_x64 arch/x86/entry/common.c:51 [inline]
       do_syscall_64+0x3b/0xb0 arch/x86/entry/common.c:81
       entry_SYSCALL_64_after_hwframe+0x68/0xd2

-> #0 (nr_node_list_lock){+...}-{2:2}:
       check_prev_add kernel/locking/lockdep.c:3090 [inline]
       check_prevs_add kernel/locking/lockdep.c:3209 [inline]
       validate_chain+0x1661/0x5950 kernel/locking/lockdep.c:3825
       __lock_acquire+0x125b/0x1f80 kernel/locking/lockdep.c:5049
       lock_acquire+0x1f8/0x5a0 kernel/locking/lockdep.c:5662
       __raw_spin_lock_bh include/linux/spinlock_api_smp.h:126 [inline]
       _raw_spin_lock_bh+0x31/0x40 kernel/locking/spinlock.c:178
       spin_lock_bh include/linux/spinlock.h:356 [inline]
       nr_rt_device_down+0xb1/0x7b0 net/netrom/nr_route.c:517
       nr_device_event+0x12b/0x140 net/netrom/af_netrom.c:126
       notifier_call_chain kernel/notifier.c:87 [inline]
       raw_notifier_call_chain+0xd0/0x170 kernel/notifier.c:455
       __dev_notify_flags+0x304/0x610
       dev_change_flags+0xe7/0x190 net/core/dev.c:8669
       dev_ifsioc+0x177/0x1160 net/core/dev_ioctl.c:327
       dev_ioctl+0x508/0xf70 net/core/dev_ioctl.c:588
       sock_do_ioctl+0x26b/0x450 net/socket.c:1218
       sock_ioctl+0x47f/0x770 net/socket.c:1321
       vfs_ioctl fs/ioctl.c:51 [inline]
       __do_sys_ioctl fs/ioctl.c:870 [inline]
       __se_sys_ioctl+0xf1/0x160 fs/ioctl.c:856
       do_syscall_x64 arch/x86/entry/common.c:51 [inline]
       do_syscall_64+0x3b/0xb0 arch/x86/entry/common.c:81
       entry_SYSCALL_64_after_hwframe+0x68/0xd2

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.3.46/4536:
 #0: ffffffff8e50b428 (rtnl_mutex){+.+.}-{3:3}, at: dev_ioctl+0x4f5/0xf70 net/core/dev_ioctl.c:587
 #1: ffffffff8e653238 (nr_neigh_list_lock){+...}-{2:2}, at: spin_lock_bh include/linux/spinlock.h:356 [inline]
 #1: ffffffff8e653238 (nr_neigh_list_lock){+...}-{2:2}, at: nr_rt_device_down+0x24/0x7b0 net/netrom/nr_route.c:514

stack backtrace:
CPU: 1 PID: 4536 Comm: syz.3.46 Not tainted 6.1.123-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/13/2024
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:88 [inline]
 dump_stack_lvl+0x1e3/0x2cb lib/dump_stack.c:106
 check_noncircular+0x2fa/0x3b0 kernel/locking/lockdep.c:2170
 check_prev_add kernel/locking/lockdep.c:3090 [inline]
 check_prevs_add kernel/locking/lockdep.c:3209 [inline]
 validate_chain+0x1661/0x5950 kernel/locking/lockdep.c:3825
 __lock_acquire+0x125b/0x1f80 kernel/locking/lockdep.c:5049
 lock_acquire+0x1f8/0x5a0 kernel/locking/lockdep.c:5662
 __raw_spin_lock_bh include/linux/spinlock_api_smp.h:126 [inline]
 _raw_spin_lock_bh+0x31/0x40 kernel/locking/spinlock.c:178
 spin_lock_bh include/linux/spinlock.h:356 [inline]
 nr_rt_device_down+0xb1/0x7b0 net/netrom/nr_route.c:517
 nr_device_event+0x12b/0x140 net/netrom/af_netrom.c:126
 notifier_call_chain kernel/notifier.c:87 [inline]
 raw_notifier_call_chain+0xd0/0x170 kernel/notifier.c:455
 __dev_notify_flags+0x304/0x610
 dev_change_flags+0xe7/0x190 net/core/dev.c:8669
 dev_ifsioc+0x177/0x1160 net/core/dev_ioctl.c:327
 dev_ioctl+0x508/0xf70 net/core/dev_ioctl.c:588
 sock_do_ioctl+0x26b/0x450 net/socket.c:1218
 sock_ioctl+0x47f/0x770 net/socket.c:1321
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:870 [inline]
 __se_sys_ioctl+0xf1/0x160 fs/ioctl.c:856
 do_syscall_x64 arch/x86/entry/common.c:51 [inline]
 do_syscall_64+0x3b/0xb0 arch/x86/entry/common.c:81
 entry_SYSCALL_64_after_hwframe+0x68/0xd2
RIP: 0033:0x7f6d81585d29
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:00007f6d813ff038 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007f6d81775fa0 RCX: 00007f6d81585d29
RDX: 0000000020000000 RSI: 0000000000008914 RDI: 0000000000000007
RBP: 00007f6d81601b08 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 0000000000000000 R14: 00007f6d81775fa0 R15: 00007ffcda17a5c8
 </TASK>