syzbot

======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
syz.2.808/6436 is trying to acquire lock:
ffffffff96e33ec8 (&obj_hash[i].lock){-.-.}-{2:2}, at: __debug_check_no_obj_freed lib/debugobjects.c:968 [inline]
ffffffff96e33ec8 (&obj_hash[i].lock){-.-.}-{2:2}, at: debug_check_no_obj_freed+0x136/0x530 lib/debugobjects.c:1009

but task is already holding lock:
ffff88805291a238 (&trie->lock){-.-.}-{2:2}, at: trie_update_elem+0xc4/0xe90 kernel/bpf/lpm_trie.c:335

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #1 (&trie->lock){-.-.}-{2:2}:
       __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline]
       _raw_spin_lock_irqsave+0xa4/0xf0 kernel/locking/spinlock.c:162
       trie_delete_elem+0x90/0x690 kernel/bpf/lpm_trie.c:467
       0xffffffffa0000a0e
       bpf_dispatcher_nop_func include/linux/bpf.h:1011 [inline]
       __bpf_prog_run include/linux/filter.h:596 [inline]
       bpf_prog_run include/linux/filter.h:610 [inline]
       __bpf_trace_run kernel/trace/bpf_trace.c:2285 [inline]
       bpf_trace_run2+0x30a/0x3b0 kernel/trace/bpf_trace.c:2324
       trace_contention_end+0x13f/0x190 include/trace/events/lock.h:122
       __pv_queued_spin_lock_slowpath+0x7e8/0x9c0 kernel/locking/qspinlock.c:560
       pv_queued_spin_lock_slowpath arch/x86/include/asm/paravirt.h:591 [inline]
       queued_spin_lock_slowpath+0x43/0x50 arch/x86/include/asm/qspinlock.h:51
       queued_spin_lock include/asm-generic/qspinlock.h:114 [inline]
       do_raw_spin_lock+0x217/0x280 kernel/locking/spinlock_debug.c:115
       __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:111 [inline]
       _raw_spin_lock_irqsave+0xb0/0xf0 kernel/locking/spinlock.c:162
       __debug_check_no_obj_freed lib/debugobjects.c:968 [inline]
       debug_check_no_obj_freed+0x136/0x530 lib/debugobjects.c:1009
       slab_free_hook mm/slub.c:1704 [inline]
       slab_free_freelist_hook+0xd2/0x1a0 mm/slub.c:1755
       slab_free mm/slub.c:3687 [inline]
       kmem_cache_free+0xf7/0x290 mm/slub.c:3709
       kernfs_put+0x319/0x490 fs/kernfs/dir.c:568
       kernfs_remove_by_name_ns+0xe0/0x150 fs/kernfs/dir.c:1668
       kernfs_remove_by_name include/linux/kernfs.h:622 [inline]
       remove_files fs/sysfs/group.c:28 [inline]
       sysfs_remove_group+0xf8/0x290 fs/sysfs/group.c:288
       sysfs_remove_groups+0x50/0xa0 fs/sysfs/group.c:312
       device_remove_groups drivers/base/core.c:2759 [inline]
       device_remove_attrs+0x205/0x250 drivers/base/core.c:2979
       device_del+0x620/0xa70 drivers/base/core.c:3884
       unregister_netdevice_many+0x1393/0x1840 net/core/dev.c:11017
       unregister_netdevice_queue+0x31c/0x360 net/core/dev.c:10921
       unregister_netdevice include/linux/netdevice.h:3075 [inline]
       __tun_detach+0xd4a/0x1500 drivers/net/tun.c:685
       tun_detach drivers/net/tun.c:701 [inline]
       tun_chr_close+0x109/0x1b0 drivers/net/tun.c:3492
       __fput+0x22c/0x920 fs/file_table.c:320
       task_work_run+0x1ca/0x250 kernel/task_work.c:203
       resume_user_mode_work include/linux/resume_user_mode.h:49 [inline]
       exit_to_user_mode_loop+0xe6/0x110 kernel/entry/common.c:177
       exit_to_user_mode_prepare+0xee/0x180 kernel/entry/common.c:210
       __syscall_exit_to_user_mode_work kernel/entry/common.c:292 [inline]
       syscall_exit_to_user_mode+0x16/0x40 kernel/entry/common.c:303
       do_syscall_64+0x58/0xa0 arch/x86/entry/common.c:87
       entry_SYSCALL_64_after_hwframe+0x68/0xd2

-> #0 (&obj_hash[i].lock){-.-.}-{2:2}:
       check_prev_add kernel/locking/lockdep.c:3090 [inline]
       check_prevs_add kernel/locking/lockdep.c:3209 [inline]
       validate_chain kernel/locking/lockdep.c:3825 [inline]
       __lock_acquire+0x2cf8/0x7c50 kernel/locking/lockdep.c:5049
       lock_acquire+0x1b4/0x490 kernel/locking/lockdep.c:5662
       __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline]
       _raw_spin_lock_irqsave+0xa4/0xf0 kernel/locking/spinlock.c:162
       __debug_check_no_obj_freed lib/debugobjects.c:968 [inline]
       debug_check_no_obj_freed+0x136/0x530 lib/debugobjects.c:1009
       slab_free_hook mm/slub.c:1704 [inline]
       slab_free_freelist_hook+0xd2/0x1a0 mm/slub.c:1755
       slab_free mm/slub.c:3687 [inline]
       __kmem_cache_free+0xb6/0x1f0 mm/slub.c:3700
       trie_update_elem+0x6c1/0xe90 kernel/bpf/lpm_trie.c:444
       bpf_map_update_value+0x59e/0x670 kernel/bpf/syscall.c:228
       generic_map_update_batch+0x569/0x850 kernel/bpf/syscall.c:1709
       bpf_map_do_batch+0x466/0x600 kernel/bpf/syscall.c:-1
       __sys_bpf+0x65f/0x6d0 kernel/bpf/syscall.c:-1
       __do_sys_bpf kernel/bpf/syscall.c:5131 [inline]
       __se_sys_bpf kernel/bpf/syscall.c:5129 [inline]
       __x64_sys_bpf+0x78/0x90 kernel/bpf/syscall.c:5129
       do_syscall_x64 arch/x86/entry/common.c:51 [inline]
       do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:81
       entry_SYSCALL_64_after_hwframe+0x68/0xd2

other info that might help us debug this:

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(&trie->lock);
                               lock(&obj_hash[i].lock);
                               lock(&trie->lock);
  lock(&obj_hash[i].lock);

 *** DEADLOCK ***

2 locks held by syz.2.808/6436:
 #0: ffffffff8cb2abe0 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire include/linux/rcupdate.h:350 [inline]
 #0: ffffffff8cb2abe0 (rcu_read_lock){....}-{1:2}, at: rcu_read_lock include/linux/rcupdate.h:791 [inline]
 #0: ffffffff8cb2abe0 (rcu_read_lock){....}-{1:2}, at: bpf_map_update_value+0x375/0x670 kernel/bpf/syscall.c:227
 #1: ffff88805291a238 (&trie->lock){-.-.}-{2:2}, at: trie_update_elem+0xc4/0xe90 kernel/bpf/lpm_trie.c:335

stack backtrace:
CPU: 0 PID: 6436 Comm: syz.2.808 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/18/2025
Call Trace:
 <TASK>
 dump_stack_lvl+0x168/0x22e lib/dump_stack.c:106
 check_noncircular+0x274/0x310 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 kernel/locking/lockdep.c:3825 [inline]
 __lock_acquire+0x2cf8/0x7c50 kernel/locking/lockdep.c:5049
 lock_acquire+0x1b4/0x490 kernel/locking/lockdep.c:5662
 __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline]
 _raw_spin_lock_irqsave+0xa4/0xf0 kernel/locking/spinlock.c:162
 __debug_check_no_obj_freed lib/debugobjects.c:968 [inline]
 debug_check_no_obj_freed+0x136/0x530 lib/debugobjects.c:1009
 slab_free_hook mm/slub.c:1704 [inline]
 slab_free_freelist_hook+0xd2/0x1a0 mm/slub.c:1755
 slab_free mm/slub.c:3687 [inline]
 __kmem_cache_free+0xb6/0x1f0 mm/slub.c:3700
 trie_update_elem+0x6c1/0xe90 kernel/bpf/lpm_trie.c:444
 bpf_map_update_value+0x59e/0x670 kernel/bpf/syscall.c:228
 generic_map_update_batch+0x569/0x850 kernel/bpf/syscall.c:1709
 bpf_map_do_batch+0x466/0x600 kernel/bpf/syscall.c:-1
 __sys_bpf+0x65f/0x6d0 kernel/bpf/syscall.c:-1
 __do_sys_bpf kernel/bpf/syscall.c:5131 [inline]
 __se_sys_bpf kernel/bpf/syscall.c:5129 [inline]
 __x64_sys_bpf+0x78/0x90 kernel/bpf/syscall.c:5129
 do_syscall_x64 arch/x86/entry/common.c:51 [inline]
 do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:81
 entry_SYSCALL_64_after_hwframe+0x68/0xd2
RIP: 0033:0x7fb875b8eec9
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:00007fb8769b5038 EFLAGS: 00000246 ORIG_RAX: 0000000000000141
RAX: ffffffffffffffda RBX: 00007fb875de5fa0 RCX: 00007fb875b8eec9
RDX: 0000000000000038 RSI: 0000200000000240 RDI: 000000000000001a
RBP: 00007fb875c11f91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fb875de6038 R14: 00007fb875de5fa0 R15: 00007ffd49222088
 </TASK>