possible deadlock in nr_remove_neigh

Status: upstream: reported C repro on 2025/01/22 07:32
Bug presence: origin:upstream
[Documentation on labels]
Reported-by: syzbot+a3b4fb520bc52e171081@syzkaller.appspotmail.com
First crash: 547d, last: 56d
Fix bisection: failed (error log, bisect log)
  
▶ ▼ Bug presence (1)
Date Name Commit Repro Result
2025/01/22 upstream (ToT) c4b9570cfb63 C [report] possible deadlock in nr_remove_neigh
▶ ▼ Similar bugs (4)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
linux-6.6 possible deadlock in nr_remove_neigh 4 1 218d 218d 0/2 auto-obsoleted due to no activity on 2026/03/27 08:30
upstream possible deadlock in nr_remove_neigh (2) hams 4 C unreliable error 1122 90d 570d 0/29 upstream: reported C repro on 2024/12/30 02:36
linux-6.1 possible deadlock in nr_remove_neigh 4 13 443d 570d 0/3 auto-obsoleted due to no activity on 2025/08/13 20:50
linux-6.1 possible deadlock in nr_remove_neigh (2) origin:upstream 4 C error 10 114d 308d 0/3 upstream: reported C repro on 2025/09/18 00:16
▶ ▼ Last patch testing requests (10)
Created Duration User Patch Repo Result
2026/05/27 16:13 1h10m retest repro linux-5.15.y report log
2026/05/27 16:13 22m retest repro linux-5.15.y report log
2026/05/27 16:13 31m retest repro linux-5.15.y report log
2026/05/13 13:10 17m retest repro linux-5.15.y report log
2026/03/18 02:40 18m retest repro linux-5.15.y report log
2026/03/18 02:40 11m retest repro linux-5.15.y report log
2026/03/14 12:50 13m retest repro linux-5.15.y error
2026/03/14 12:49 7m retest repro linux-5.15.y error
2026/02/28 12:35 10m retest repro linux-5.15.y report log
2026/01/06 12:46 13m retest repro linux-5.15.y report log

Sample crash report:
======================================================
WARNING: possible circular locking dependency detected
5.15.176-syzkaller #0 Not tainted
------------------------------------------------------
syz-executor451/4133 is trying to acquire lock:
ffff800016dd88f8 (nr_neigh_list_lock){+...}-{2:2}, at: spin_lock_bh include/linux/spinlock.h:368 [inline]
ffff800016dd88f8 (nr_neigh_list_lock){+...}-{2:2}, at: nr_remove_neigh+0x30/0xec net/netrom/nr_route.c:307

but task is already holding lock:
ffff0000d12f7a70 (&nr_node->node_lock){+...}-{2:2}, at: spin_lock_bh include/linux/spinlock.h:368 [inline]
ffff0000d12f7a70 (&nr_node->node_lock){+...}-{2:2}, at: nr_node_lock include/net/netrom.h:151 [inline]
ffff0000d12f7a70 (&nr_node->node_lock){+...}-{2:2}, at: nr_add_node+0xe1c/0x1fc4 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){+...}-{2:2}:
       __raw_spin_lock_bh include/linux/spinlock_api_smp.h:135 [inline]
       _raw_spin_lock_bh+0x124/0x1c4 kernel/locking/spinlock.c:178
       spin_lock_bh include/linux/spinlock.h:368 [inline]
       nr_node_lock include/net/netrom.h:151 [inline]
       nr_rt_device_down+0x130/0x710 net/netrom/nr_route.c:519
       nr_device_event+0x134/0x160 net/netrom/af_netrom.c:126
       notifier_call_chain kernel/notifier.c:83 [inline]
       raw_notifier_call_chain+0xd4/0x164 kernel/notifier.c:391
       call_netdevice_notifiers_info net/core/dev.c:2018 [inline]
       call_netdevice_notifiers_extack net/core/dev.c:2030 [inline]
       call_netdevice_notifiers net/core/dev.c:2044 [inline]
       dev_close_many+0x2fc/0x468 net/core/dev.c:1619
       dev_close+0x174/0x250 net/core/dev.c:1641
       bpq_device_event+0x314/0x814 drivers/net/hamradio/bpqether.c:548
       notifier_call_chain kernel/notifier.c:83 [inline]
       raw_notifier_call_chain+0xd4/0x164 kernel/notifier.c:391
       call_netdevice_notifiers_info net/core/dev.c:2018 [inline]
       call_netdevice_notifiers_extack net/core/dev.c:2030 [inline]
       call_netdevice_notifiers net/core/dev.c:2044 [inline]
       dev_close_many+0x2fc/0x468 net/core/dev.c:1619
       dev_close+0x174/0x250 net/core/dev.c:1641
       bond_setup_by_slave+0x70/0x314 drivers/net/bonding/bond_main.c:1471
       bond_enslave+0x628/0x3198 drivers/net/bonding/bond_main.c:1855
       bond_do_ioctl+0x264/0xd0c drivers/net/bonding/bond_main.c:4238
       dev_siocbond net/core/dev_ioctl.c:270 [inline]
       dev_ifsioc+0xc38/0xfe4 net/core/dev_ioctl.c:417
       dev_ioctl+0x4e0/0xd3c net/core/dev_ioctl.c:587
       sock_do_ioctl+0x1dc/0x2dc net/socket.c:1154
       sock_ioctl+0x4f0/0x8ac net/socket.c:1257
       vfs_ioctl fs/ioctl.c:51 [inline]
       __do_sys_ioctl fs/ioctl.c:874 [inline]
       __se_sys_ioctl fs/ioctl.c:860 [inline]
       __arm64_sys_ioctl+0x14c/0x1c8 fs/ioctl.c:860
       __invoke_syscall arch/arm64/kernel/syscall.c:38 [inline]
       invoke_syscall+0x98/0x2b8 arch/arm64/kernel/syscall.c:52
       el0_svc_common+0x138/0x258 arch/arm64/kernel/syscall.c:142
       do_el0_svc+0x58/0x14c arch/arm64/kernel/syscall.c:181
       el0_svc+0x7c/0x1f0 arch/arm64/kernel/entry-common.c:608
       el0t_64_sync_handler+0x84/0xe4 arch/arm64/kernel/entry-common.c:626
       el0t_64_sync+0x1a0/0x1a4 arch/arm64/kernel/entry.S:584

-> #1 (nr_node_list_lock){+...}-{2:2}:
       __raw_spin_lock_bh include/linux/spinlock_api_smp.h:135 [inline]
       _raw_spin_lock_bh+0x124/0x1c4 kernel/locking/spinlock.c:178
       spin_lock_bh include/linux/spinlock.h:368 [inline]
       nr_rt_device_down+0xac/0x710 net/netrom/nr_route.c:517
       nr_device_event+0x134/0x160 net/netrom/af_netrom.c:126
       notifier_call_chain kernel/notifier.c:83 [inline]
       raw_notifier_call_chain+0xd4/0x164 kernel/notifier.c:391
       call_netdevice_notifiers_info net/core/dev.c:2018 [inline]
       call_netdevice_notifiers_extack net/core/dev.c:2030 [inline]
       call_netdevice_notifiers net/core/dev.c:2044 [inline]
       dev_close_many+0x2fc/0x468 net/core/dev.c:1619
       dev_close+0x174/0x250 net/core/dev.c:1641
       bpq_device_event+0x314/0x814 drivers/net/hamradio/bpqether.c:548
       notifier_call_chain kernel/notifier.c:83 [inline]
       raw_notifier_call_chain+0xd4/0x164 kernel/notifier.c:391
       call_netdevice_notifiers_info net/core/dev.c:2018 [inline]
       call_netdevice_notifiers_extack net/core/dev.c:2030 [inline]
       call_netdevice_notifiers net/core/dev.c:2044 [inline]
       dev_close_many+0x2fc/0x468 net/core/dev.c:1619
       dev_close+0x174/0x250 net/core/dev.c:1641
       bond_setup_by_slave+0x70/0x314 drivers/net/bonding/bond_main.c:1471
       bond_enslave+0x628/0x3198 drivers/net/bonding/bond_main.c:1855
       bond_do_ioctl+0x264/0xd0c drivers/net/bonding/bond_main.c:4238
       dev_siocbond net/core/dev_ioctl.c:270 [inline]
       dev_ifsioc+0xc38/0xfe4 net/core/dev_ioctl.c:417
       dev_ioctl+0x4e0/0xd3c net/core/dev_ioctl.c:587
       sock_do_ioctl+0x1dc/0x2dc net/socket.c:1154
       sock_ioctl+0x4f0/0x8ac net/socket.c:1257
       vfs_ioctl fs/ioctl.c:51 [inline]
       __do_sys_ioctl fs/ioctl.c:874 [inline]
       __se_sys_ioctl fs/ioctl.c:860 [inline]
       __arm64_sys_ioctl+0x14c/0x1c8 fs/ioctl.c:860
       __invoke_syscall arch/arm64/kernel/syscall.c:38 [inline]
       invoke_syscall+0x98/0x2b8 arch/arm64/kernel/syscall.c:52
       el0_svc_common+0x138/0x258 arch/arm64/kernel/syscall.c:142
       do_el0_svc+0x58/0x14c arch/arm64/kernel/syscall.c:181
       el0_svc+0x7c/0x1f0 arch/arm64/kernel/entry-common.c:608
       el0t_64_sync_handler+0x84/0xe4 arch/arm64/kernel/entry-common.c:626
       el0t_64_sync+0x1a0/0x1a4 arch/arm64/kernel/entry.S:584

-> #0 (nr_neigh_list_lock){+...}-{2:2}:
       check_prev_add kernel/locking/lockdep.c:3053 [inline]
       check_prevs_add kernel/locking/lockdep.c:3172 [inline]
       validate_chain kernel/locking/lockdep.c:3788 [inline]
       __lock_acquire+0x32d4/0x7638 kernel/locking/lockdep.c:5012
       lock_acquire+0x240/0x77c kernel/locking/lockdep.c:5623
       __raw_spin_lock_bh include/linux/spinlock_api_smp.h:135 [inline]
       _raw_spin_lock_bh+0x124/0x1c4 kernel/locking/spinlock.c:178
       spin_lock_bh include/linux/spinlock.h:368 [inline]
       nr_remove_neigh+0x30/0xec net/netrom/nr_route.c:307
       nr_add_node+0x17e4/0x1fc4 net/netrom/nr_route.c:249
       nr_rt_ioctl+0xe58/0x18c8 net/netrom/nr_route.c:651
       nr_ioctl+0x14c/0x4b0 net/netrom/af_netrom.c:1253
       sock_do_ioctl+0x134/0x2dc net/socket.c:1140
       sock_ioctl+0x4f0/0x8ac net/socket.c:1257
       vfs_ioctl fs/ioctl.c:51 [inline]
       __do_sys_ioctl fs/ioctl.c:874 [inline]
       __se_sys_ioctl fs/ioctl.c:860 [inline]
       __arm64_sys_ioctl+0x14c/0x1c8 fs/ioctl.c:860
       __invoke_syscall arch/arm64/kernel/syscall.c:38 [inline]
       invoke_syscall+0x98/0x2b8 arch/arm64/kernel/syscall.c:52
       el0_svc_common+0x138/0x258 arch/arm64/kernel/syscall.c:142
       do_el0_svc+0x58/0x14c arch/arm64/kernel/syscall.c:181
       el0_svc+0x7c/0x1f0 arch/arm64/kernel/entry-common.c:608
       el0t_64_sync_handler+0x84/0xe4 arch/arm64/kernel/entry-common.c:626
       el0t_64_sync+0x1a0/0x1a4 arch/arm64/kernel/entry.S:584

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-executor451/4133:
 #0: ffff0000d12f7a70 (&nr_node->node_lock){+...}-{2:2}, at: spin_lock_bh include/linux/spinlock.h:368 [inline]
 #0: ffff0000d12f7a70 (&nr_node->node_lock){+...}-{2:2}, at: nr_node_lock include/net/netrom.h:151 [inline]
 #0: ffff0000d12f7a70 (&nr_node->node_lock){+...}-{2:2}, at: nr_add_node+0xe1c/0x1fc4 net/netrom/nr_route.c:214

stack backtrace:
CPU: 1 PID: 4133 Comm: syz-executor451 Not tainted 5.15.176-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 12/27/2024
Call trace:
 dump_backtrace+0x0/0x530 arch/arm64/kernel/stacktrace.c:152
 show_stack+0x2c/0x3c arch/arm64/kernel/stacktrace.c:216
 __dump_stack lib/dump_stack.c:88 [inline]
 dump_stack_lvl+0x108/0x170 lib/dump_stack.c:106
 dump_stack+0x1c/0x58 lib/dump_stack.c:113
 print_circular_bug+0x150/0x1b8 kernel/locking/lockdep.c:2011
 check_noncircular+0x2cc/0x378 kernel/locking/lockdep.c:2133
 check_prev_add kernel/locking/lockdep.c:3053 [inline]
 check_prevs_add kernel/locking/lockdep.c:3172 [inline]
 validate_chain kernel/locking/lockdep.c:3788 [inline]
 __lock_acquire+0x32d4/0x7638 kernel/locking/lockdep.c:5012
 lock_acquire+0x240/0x77c kernel/locking/lockdep.c:5623
 __raw_spin_lock_bh include/linux/spinlock_api_smp.h:135 [inline]
 _raw_spin_lock_bh+0x124/0x1c4 kernel/locking/spinlock.c:178
 spin_lock_bh include/linux/spinlock.h:368 [inline]
 nr_remove_neigh+0x30/0xec net/netrom/nr_route.c:307
 nr_add_node+0x17e4/0x1fc4 net/netrom/nr_route.c:249
 nr_rt_ioctl+0xe58/0x18c8 net/netrom/nr_route.c:651
 nr_ioctl+0x14c/0x4b0 net/netrom/af_netrom.c:1253
 sock_do_ioctl+0x134/0x2dc net/socket.c:1140
 sock_ioctl+0x4f0/0x8ac net/socket.c:1257
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:874 [inline]
 __se_sys_ioctl fs/ioctl.c:860 [inline]
 __arm64_sys_ioctl+0x14c/0x1c8 fs/ioctl.c:860
 __invoke_syscall arch/arm64/kernel/syscall.c:38 [inline]
 invoke_syscall+0x98/0x2b8 arch/arm64/kernel/syscall.c:52
 el0_svc_common+0x138/0x258 arch/arm64/kernel/syscall.c:142
 do_el0_svc+0x58/0x14c arch/arm64/kernel/syscall.c:181
 el0_svc+0x7c/0x1f0 arch/arm64/kernel/entry-common.c:608
 el0t_64_sync_handler+0x84/0xe4 arch/arm64/kernel/entry-common.c:626
 el0t_64_sync+0x1a0/0x1a4 arch/arm64/kernel/entry.S:584
bond0: (slave rose0): Error: Device is in use and cannot be enslaved

Crashes (25):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2025/01/22 14:35 linux-5.15.y 4735586da88e da72ac06 .config console log report syz / log C [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan-arm64 possible deadlock in nr_remove_neigh
2025/01/22 13:09 linux-5.15.y 4735586da88e da72ac06 .config console log report syz / log C [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan-arm64 possible deadlock in nr_remove_neigh
2025/01/22 11:49 linux-5.15.y 4735586da88e da72ac06 .config console log report syz / log C [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan-arm64 possible deadlock in nr_remove_neigh
2025/01/22 10:28 linux-5.15.y 4735586da88e da72ac06 .config console log report syz / log C [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan-arm64 possible deadlock in nr_remove_neigh
2026/04/06 02:58 linux-5.15.y 91d48252ad4b 4440e7c2 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan possible deadlock in nr_remove_neigh
2026/04/06 02:57 linux-5.15.y 91d48252ad4b 4440e7c2 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan possible deadlock in nr_remove_neigh
2025/06/17 12:41 linux-5.15.y 1c700860e8bc cfebc887 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan possible deadlock in nr_remove_neigh
2025/05/05 10:49 linux-5.15.y 16fdf2c7111b b0714e37 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan possible deadlock in nr_remove_neigh
2025/04/20 02:21 linux-5.15.y f7347f400572 2a20f901 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan possible deadlock in nr_remove_neigh
2025/04/19 02:02 linux-5.15.y f7347f400572 2a20f901 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan possible deadlock in nr_remove_neigh
2025/04/19 00:26 linux-5.15.y f7347f400572 2a20f901 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan possible deadlock in nr_remove_neigh
2025/04/18 05:41 linux-5.15.y f7347f400572 2a20f901 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan possible deadlock in nr_remove_neigh
2025/04/09 19:06 linux-5.15.y 0c935c049b5c 47d015b1 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan possible deadlock in nr_remove_neigh
2025/04/04 07:59 linux-5.15.y 0c935c049b5c d7ae3a11 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan possible deadlock in nr_remove_neigh
2025/04/04 01:19 linux-5.15.y 0c935c049b5c d7ae3a11 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan possible deadlock in nr_remove_neigh
2025/01/22 14:52 linux-5.15.y 4735586da88e da72ac06 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan possible deadlock in nr_remove_neigh
2025/01/22 14:48 linux-5.15.y 4735586da88e da72ac06 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan possible deadlock in nr_remove_neigh
2025/01/22 14:48 linux-5.15.y 4735586da88e da72ac06 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan possible deadlock in nr_remove_neigh
2025/04/18 03:09 linux-5.15.y f7347f400572 2a20f901 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan-arm64 possible deadlock in nr_remove_neigh
2025/04/18 03:08 linux-5.15.y f7347f400572 2a20f901 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan-arm64 possible deadlock in nr_remove_neigh
2025/04/16 17:55 linux-5.15.y f7347f400572 a95239b1 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan-arm64 possible deadlock in nr_remove_neigh
2025/04/16 17:52 linux-5.15.y f7347f400572 a95239b1 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan-arm64 possible deadlock in nr_remove_neigh
2025/03/27 09:04 linux-5.15.y 0c935c049b5c 20510e88 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan-arm64 possible deadlock in nr_remove_neigh
2025/01/24 13:26 linux-5.15.y 003148680b79 521b0ce3 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan-arm64 possible deadlock in nr_remove_neigh
2025/01/22 07:31 linux-5.15.y 4735586da88e da72ac06 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan-arm64 possible deadlock in nr_remove_neigh
* Struck through repros no longer work on HEAD.