syzbot

======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
udevd/5881 is trying to acquire lock:
ffff8880b8e29370 (krc.lock){..-.}-{2:2}, at: krc_this_cpu_lock kernel/rcu/tree.c:2959 [inline]
ffff8880b8e29370 (krc.lock){..-.}-{2:2}, at: add_ptr_to_bulk_krc_lock kernel/rcu/tree.c:3368 [inline]
ffff8880b8e29370 (krc.lock){..-.}-{2:2}, at: kvfree_call_rcu+0x15a/0x780 kernel/rcu/tree.c:3453

but task is already holding lock:
ffff8880b8e29598 (&base->lock){-.-.}-{2:2}, at: lock_timer_base+0x123/0x270 kernel/time/timer.c:999

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #1 (&base->lock){-.-.}-{2:2}:
       __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline]
       _raw_spin_lock_irqsave+0xa8/0xf0 kernel/locking/spinlock.c:162
       lock_timer_base+0x123/0x270 kernel/time/timer.c:999
       __mod_timer+0xf9/0xdb0 kernel/time/timer.c:1080
       queue_delayed_work_on+0x12a/0x1e0 kernel/workqueue.c:1987
       kvfree_call_rcu+0x541/0x780 kernel/rcu/tree.c:3481
       rtnl_register_internal+0x486/0x590 net/core/rtnetlink.c:264
       rtnl_register+0x32/0x70 net/core/rtnetlink.c:314
       ip_rt_init+0x2ec/0x390 net/ipv4/route.c:3801
       ip_init+0xe/0x20 net/ipv4/ip_output.c:1663
       inet_init+0x2c1/0x3e0 net/ipv4/af_inet.c:2024
       do_one_initcall+0x1fd/0x750 init/main.c:1250
       do_initcall_level+0x137/0x1f0 init/main.c:1312
       do_initcalls+0x69/0xd0 init/main.c:1328
       kernel_init_freeable+0x3d2/0x570 init/main.c:1565
       kernel_init+0x1d/0x1c0 init/main.c:1455
       ret_from_fork+0x48/0x80 arch/x86/kernel/process.c:152
       ret_from_fork_asm+0x11/0x20 arch/x86/entry/entry_64.S:293

-> #0 (krc.lock){..-.}-{2:2}:
       check_prev_add kernel/locking/lockdep.c:3134 [inline]
       check_prevs_add kernel/locking/lockdep.c:3253 [inline]
       validate_chain kernel/locking/lockdep.c:3869 [inline]
       __lock_acquire+0x2ddb/0x7c80 kernel/locking/lockdep.c:5137
       lock_acquire+0x197/0x410 kernel/locking/lockdep.c:5754
       __raw_spin_lock include/linux/spinlock_api_smp.h:133 [inline]
       _raw_spin_lock+0x2e/0x40 kernel/locking/spinlock.c:154
       krc_this_cpu_lock kernel/rcu/tree.c:2959 [inline]
       add_ptr_to_bulk_krc_lock kernel/rcu/tree.c:3368 [inline]
       kvfree_call_rcu+0x15a/0x780 kernel/rcu/tree.c:3453
       trie_delete_elem+0x535/0x6a0 kernel/bpf/lpm_trie.c:545
       bpf_prog_87c4e24aeb87061a+0x42/0x67
       bpf_dispatcher_nop_func include/linux/bpf.h:1224 [inline]
       __bpf_prog_run include/linux/filter.h:612 [inline]
       bpf_prog_run include/linux/filter.h:619 [inline]
       __bpf_trace_run kernel/trace/bpf_trace.c:2322 [inline]
       bpf_trace_run3+0x1e7/0x400 kernel/trace/bpf_trace.c:2362
       __bpf_trace_timer_start+0x14a/0x1b0 include/trace/events/timer.h:53
       trace_timer_start include/trace/events/timer.h:53 [inline]
       enqueue_timer+0x398/0x530 kernel/time/timer.c:609
       internal_add_timer kernel/time/timer.c:634 [inline]
       __mod_timer+0x977/0xdb0 kernel/time/timer.c:1131
       dsp_cmx_send+0x1ab8/0x1b40 drivers/isdn/mISDN/dsp_cmx.c:1839
       call_timer_fn+0x16e/0x530 kernel/time/timer.c:1701
       expire_timers kernel/time/timer.c:1752 [inline]
       __run_timers+0x52d/0x7d0 kernel/time/timer.c:2023
       run_timer_softirq+0x67/0xf0 kernel/time/timer.c:2036
       handle_softirqs+0x280/0x820 kernel/softirq.c:578
       __do_softirq kernel/softirq.c:612 [inline]
       invoke_softirq kernel/softirq.c:452 [inline]
       __irq_exit_rcu+0xc7/0x190 kernel/softirq.c:661
       irq_exit_rcu+0x9/0x20 kernel/softirq.c:673
       instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1088 [inline]
       sysvec_apic_timer_interrupt+0xa4/0xc0 arch/x86/kernel/apic/apic.c:1088
       asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:687
       i_user_ns include/linux/fs.h:1326 [inline]
       i_uid_into_vfsuid include/linux/fs.h:1365 [inline]
       acl_permission_check fs/namei.c:346 [inline]
       generic_permission+0x80/0x590 fs/namei.c:408
       do_inode_permission fs/namei.c:469 [inline]
       inode_permission+0x94/0x480 fs/namei.c:529
       may_lookup fs/namei.c:1728 [inline]
       link_path_walk+0x286/0xe00 fs/namei.c:2279
       path_lookupat+0x9d/0x440 fs/namei.c:2490
       filename_lookup+0x1f4/0x510 fs/namei.c:2520
       vfs_statx+0x113/0x6d0 fs/stat.c:244
       vfs_fstatat+0x12a/0x1b0 fs/stat.c:299
       __do_sys_newfstatat fs/stat.c:463 [inline]
       __se_sys_newfstatat fs/stat.c:457 [inline]
       __x64_sys_newfstatat+0x117/0x190 fs/stat.c:457
       do_syscall_x64 arch/x86/entry/common.c:51 [inline]
       do_syscall_64+0x55/0xb0 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(&base->lock);
                               lock(krc.lock);
                               lock(&base->lock);
  lock(krc.lock);

 *** DEADLOCK ***

5 locks held by udevd/5881:
 #0: ffffffff8cd2ff20 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire include/linux/rcupdate.h:334 [inline]
 #0: ffffffff8cd2ff20 (rcu_read_lock){....}-{1:2}, at: rcu_read_lock include/linux/rcupdate.h:786 [inline]
 #0: ffffffff8cd2ff20 (rcu_read_lock){....}-{1:2}, at: path_init+0x144/0x1200 fs/namei.c:2370
 #1: ffffc90000007c00 ((&dsp_spl_tl)){+.-.}-{0:0}, at: call_timer_fn+0xbf/0x530 kernel/time/timer.c:1698
 #2: ffffffff8dd23618 (dsp_lock){..-.}-{2:2}, at: dsp_cmx_send+0x26/0x1b40 drivers/isdn/mISDN/dsp_cmx.c:1632
 #3: ffff8880b8e29598 (&base->lock){-.-.}-{2:2}, at: lock_timer_base+0x123/0x270 kernel/time/timer.c:999
 #4: ffffffff8cd2ff20 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire include/linux/rcupdate.h:334 [inline]
 #4: ffffffff8cd2ff20 (rcu_read_lock){....}-{1:2}, at: rcu_read_lock include/linux/rcupdate.h:786 [inline]
 #4: ffffffff8cd2ff20 (rcu_read_lock){....}-{1:2}, at: __bpf_trace_run kernel/trace/bpf_trace.c:2321 [inline]
 #4: ffffffff8cd2ff20 (rcu_read_lock){....}-{1:2}, at: bpf_trace_run3+0xf4/0x400 kernel/trace/bpf_trace.c:2362

stack backtrace:
CPU: 0 PID: 5881 Comm: udevd Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
Call Trace:
 <IRQ>
 dump_stack_lvl+0x16c/0x230 lib/dump_stack.c:106
 check_noncircular+0x2bd/0x3c0 kernel/locking/lockdep.c:2187
 check_prev_add kernel/locking/lockdep.c:3134 [inline]
 check_prevs_add kernel/locking/lockdep.c:3253 [inline]
 validate_chain kernel/locking/lockdep.c:3869 [inline]
 __lock_acquire+0x2ddb/0x7c80 kernel/locking/lockdep.c:5137
 lock_acquire+0x197/0x410 kernel/locking/lockdep.c:5754
 __raw_spin_lock include/linux/spinlock_api_smp.h:133 [inline]
 _raw_spin_lock+0x2e/0x40 kernel/locking/spinlock.c:154
 krc_this_cpu_lock kernel/rcu/tree.c:2959 [inline]
 add_ptr_to_bulk_krc_lock kernel/rcu/tree.c:3368 [inline]
 kvfree_call_rcu+0x15a/0x780 kernel/rcu/tree.c:3453
 trie_delete_elem+0x535/0x6a0 kernel/bpf/lpm_trie.c:545
 bpf_prog_87c4e24aeb87061a+0x42/0x67
 bpf_dispatcher_nop_func include/linux/bpf.h:1224 [inline]
 __bpf_prog_run include/linux/filter.h:612 [inline]
 bpf_prog_run include/linux/filter.h:619 [inline]
 __bpf_trace_run kernel/trace/bpf_trace.c:2322 [inline]
 bpf_trace_run3+0x1e7/0x400 kernel/trace/bpf_trace.c:2362
 __bpf_trace_timer_start+0x14a/0x1b0 include/trace/events/timer.h:53
 trace_timer_start include/trace/events/timer.h:53 [inline]
 enqueue_timer+0x398/0x530 kernel/time/timer.c:609
 internal_add_timer kernel/time/timer.c:634 [inline]
 __mod_timer+0x977/0xdb0 kernel/time/timer.c:1131
 dsp_cmx_send+0x1ab8/0x1b40 drivers/isdn/mISDN/dsp_cmx.c:1839
 call_timer_fn+0x16e/0x530 kernel/time/timer.c:1701
 expire_timers kernel/time/timer.c:1752 [inline]
 __run_timers+0x52d/0x7d0 kernel/time/timer.c:2023
 run_timer_softirq+0x67/0xf0 kernel/time/timer.c:2036
 handle_softirqs+0x280/0x820 kernel/softirq.c:578
 __do_softirq kernel/softirq.c:612 [inline]
 invoke_softirq kernel/softirq.c:452 [inline]
 __irq_exit_rcu+0xc7/0x190 kernel/softirq.c:661
 irq_exit_rcu+0x9/0x20 kernel/softirq.c:673
 instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1088 [inline]
 sysvec_apic_timer_interrupt+0xa4/0xc0 arch/x86/kernel/apic/apic.c:1088
 </IRQ>
 <TASK>
 asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:687
RIP: 0010:i_user_ns include/linux/fs.h:1326 [inline]
RIP: 0010:i_uid_into_vfsuid include/linux/fs.h:1365 [inline]
RIP: 0010:acl_permission_check fs/namei.c:346 [inline]
RIP: 0010:generic_permission+0x80/0x590 fs/namei.c:408
Code: ef 03 41 80 3c 17 00 74 12 48 89 ef e8 69 3d ee ff 48 ba 00 00 00 00 00 fc ff df 41 bc a0 07 00 00 48 89 6c 24 18 4c 03 65 00 <4c> 89 e0 48 c1 e8 03 80 3c 10 00 74 12 4c 89 e7 e8 3b 3d ee ff 48
RSP: 0018:ffffc9000465f818 EFLAGS: 00000286
RAX: 0000000000000000 RBX: ffff88801fe50cb0 RCX: ffff888027329e00
RDX: dffffc0000000000 RSI: ffff88801fe50cb0 RDI: ffffffff8ce64540
RBP: ffff88801fe50ce8 R08: ffff888027329e00 R09: 0000000000000002
R10: 000000000000002f R11: 0000000000000000 R12: ffff88814e2907a0
R13: ffffffff8ce64540 R14: 00000000000041ed R15: 1ffff11003fca19d
 do_inode_permission fs/namei.c:469 [inline]
 inode_permission+0x94/0x480 fs/namei.c:529
 may_lookup fs/namei.c:1728 [inline]
 link_path_walk+0x286/0xe00 fs/namei.c:2279
 path_lookupat+0x9d/0x440 fs/namei.c:2490
 filename_lookup+0x1f4/0x510 fs/namei.c:2520
 vfs_statx+0x113/0x6d0 fs/stat.c:244
 vfs_fstatat+0x12a/0x1b0 fs/stat.c:299
 __do_sys_newfstatat fs/stat.c:463 [inline]
 __se_sys_newfstatat fs/stat.c:457 [inline]
 __x64_sys_newfstatat+0x117/0x190 fs/stat.c:457
 do_syscall_x64 arch/x86/entry/common.c:51 [inline]
 do_syscall_64+0x55/0xb0 arch/x86/entry/common.c:81
 entry_SYSCALL_64_after_hwframe+0x68/0xd2
RIP: 0033:0x7f4ea3b11b0a
Code: 48 8b 15 f1 f2 0d 00 f7 d8 64 89 02 b8 ff ff ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 41 89 ca b8 06 01 00 00 0f 05 <3d> 00 f0 ff ff 77 07 31 c0 c3 0f 1f 40 00 48 8b 15 b9 f2 0d 00 f7
RSP: 002b:00007fff922d6688 EFLAGS: 00000246 ORIG_RAX: 0000000000000106
RAX: ffffffffffffffda RBX: 0000000000006180 RCX: 00007f4ea3b11b0a
RDX: 00007fff922d66b0 RSI: 0000564e998280f0 RDI: 00000000ffffff9c
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000564e99828450
R10: 0000000000000100 R11: 0000000000000246 R12: 0000000000000000
R13: 0000000000000000 R14: 0000564e998280f0 R15: 0000564e99828e00
 </TASK>
----------------
Code disassembly (best guess):
   0:	ef                   	out    %eax,(%dx)
   1:	03 41 80             	add    -0x80(%rcx),%eax
   4:	3c 17                	cmp    $0x17,%al
   6:	00 74 12 48          	add    %dh,0x48(%rdx,%rdx,1)
   a:	89 ef                	mov    %ebp,%edi
   c:	e8 69 3d ee ff       	call   0xffee3d7a
  11:	48 ba 00 00 00 00 00 	movabs $0xdffffc0000000000,%rdx
  18:	fc ff df
  1b:	41 bc a0 07 00 00    	mov    $0x7a0,%r12d
  21:	48 89 6c 24 18       	mov    %rbp,0x18(%rsp)
  26:	4c 03 65 00          	add    0x0(%rbp),%r12
* 2a:	4c 89 e0             	mov    %r12,%rax <-- trapping instruction
  2d:	48 c1 e8 03          	shr    $0x3,%rax
  31:	80 3c 10 00          	cmpb   $0x0,(%rax,%rdx,1)
  35:	74 12                	je     0x49
  37:	4c 89 e7             	mov    %r12,%rdi
  3a:	e8 3b 3d ee ff       	call   0xffee3d7a
  3f:	48                   	rex.W