------------[ cut here ]------------
kobject: 'loop4' (00000000afcb2025): kobject_uevent_env
ODEBUG: free active (active state 1) object type: rcu_head hint:           (null)
WARNING: CPU: 1 PID: 32202 at lib/debugobjects.c:329 debug_print_object+0x16a/0x210 lib/debugobjects.c:326
kobject: 'loop4' (00000000afcb2025): fill_kobj_path: path = '/devices/virtual/block/loop4'
Kernel panic - not syncing: panic_on_warn set ...
CPU: 1 PID: 32202 Comm: udevd Not tainted 4.19.0-rc8-next-20181016+ #95
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
kobject: 'loop2' (00000000ce5528b1): kobject_uevent_env
Call Trace:
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0x244/0x39d lib/dump_stack.c:113
 panic+0x2ad/0x55c kernel/panic.c:188
kobject: 'loop2' (00000000ce5528b1): fill_kobj_path: path = '/devices/virtual/block/loop2'
 __warn.cold.8+0x20/0x45 kernel/panic.c:540
 report_bug+0x254/0x2d0 lib/bug.c:186
 fixup_bug arch/x86/kernel/traps.c:178 [inline]
 do_error_trap+0x11b/0x200 arch/x86/kernel/traps.c:271
 do_invalid_op+0x36/0x40 arch/x86/kernel/traps.c:290
 invalid_op+0x14/0x20 arch/x86/entry/entry_64.S:969
RIP: 0010:debug_print_object+0x16a/0x210 lib/debugobjects.c:326
Code: 40 88 48 89 fa 48 c1 ea 03 80 3c 02 00 0f 85 92 00 00 00 48 8b 14 dd 80 fc 40 88 4c 89 fe 48 c7 c7 20 f2 40 88 e8 96 25 b5 fd <0f> 0b 83 05 79 6a 60 06 01 48 83 c4 18 5b 41 5c 41 5d 41 5e 41 5f
RSP: 0018:ffff880187db6858 EFLAGS: 00010082
RAX: 0000000000000000 RBX: 0000000000000003 RCX: 0000000000000000
RDX: 0000000000000000 RSI: ffffffff81647515 RDI: 0000000000000005
RBP: ffff880187db6898 R08: ffff8801c541a480 R09: ffffed003b5e3eda
R10: ffffed003b5e3eda R11: ffff8801daf1f6d7 R12: 0000000000000001
R13: ffffffff8939a4e0 R14: 0000000000000000 R15: ffffffff8840f6c0
 __debug_check_no_obj_freed lib/debugobjects.c:786 [inline]
 debug_check_no_obj_freed+0x3ae/0x58d lib/debugobjects.c:818
 kmem_cache_free+0x202/0x290 mm/slab.c:3759
 free_task_struct kernel/fork.c:163 [inline]
 free_task+0x16e/0x1f0 kernel/fork.c:457
 __put_task_struct+0x2e6/0x620 kernel/fork.c:730
 put_task_struct include/linux/sched/task.h:96 [inline]
 finish_task_switch+0x66b/0x920 kernel/sched/core.c:2715
kobject: 'loop2' (00000000ce5528b1): kobject_uevent_env
 context_switch kernel/sched/core.c:2834 [inline]
 __schedule+0x8d7/0x21d0 kernel/sched/core.c:3480
kobject: 'loop2' (00000000ce5528b1): fill_kobj_path: path = '/devices/virtual/block/loop2'
 preempt_schedule_common+0x1f/0xe0 kernel/sched/core.c:3604
 preempt_schedule+0x4d/0x60 kernel/sched/core.c:3630
 ___preempt_schedule+0x16/0x18
 __raw_spin_unlock include/linux/spinlock_api_smp.h:152 [inline]
 _raw_spin_unlock+0x3f/0x50 kernel/locking/spinlock.c:176
 spin_unlock include/linux/spinlock.h:369 [inline]
 zap_pte_range mm/memory.c:1148 [inline]
 zap_pmd_range mm/memory.c:1193 [inline]
 zap_pud_range mm/memory.c:1222 [inline]
 zap_p4d_range mm/memory.c:1243 [inline]
 unmap_page_range+0x18f7/0x2930 mm/memory.c:1264
 unmap_single_vma+0x19b/0x310 mm/memory.c:1309
 unmap_vmas+0x125/0x200 mm/memory.c:1339
 exit_mmap+0x2be/0x590 mm/mmap.c:3145
 __mmput kernel/fork.c:1045 [inline]
 mmput+0x247/0x610 kernel/fork.c:1066
 exec_mmap fs/exec.c:1043 [inline]
 flush_old_exec+0xb91/0x21b0 fs/exec.c:1276
 load_elf_binary+0xa39/0x5620 fs/binfmt_elf.c:869
 search_binary_handler+0x17d/0x570 fs/exec.c:1653
 exec_binprm fs/exec.c:1695 [inline]
 __do_execve_file.isra.33+0x1661/0x25d0 fs/exec.c:1819
 do_execveat_common fs/exec.c:1866 [inline]
 do_execve fs/exec.c:1883 [inline]
 __do_sys_execve fs/exec.c:1964 [inline]
 __se_sys_execve fs/exec.c:1959 [inline]
 __x64_sys_execve+0x8f/0xc0 fs/exec.c:1959
 do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x7fcb91ac8207
Code: Bad RIP value.
RSP: 002b:00007ffd1af390c8 EFLAGS: 00000202 ORIG_RAX: 000000000000003b
RAX: ffffffffffffffda RBX: 00000000ffffffff RCX: 00007fcb91ac8207
RDX: 000000000247f200 RSI: 00007ffd1af391c0 RDI: 00007ffd1af3a1d0
RBP: 0000000000625500 R08: 00000000000015a6 R09: 00000000000015a6
R10: 0000000000000000 R11: 0000000000000202 R12: 000000000247f200
R13: 0000000000000007 R14: 0000000002466250 R15: 0000000000000005

======================================================
WARNING: possible circular locking dependency detected
4.19.0-rc8-next-20181016+ #95 Not tainted
------------------------------------------------------
udevd/32202 is trying to acquire lock:
000000009c650796 ((console_sem).lock){-.-.}, at: down_trylock+0x13/0x70 kernel/locking/semaphore.c:136

but task is already holding lock:
00000000dc7dcbd1 (&obj_hash[i].lock){-.-.}, at: __debug_check_no_obj_freed lib/debugobjects.c:777 [inline]
00000000dc7dcbd1 (&obj_hash[i].lock){-.-.}, at: debug_check_no_obj_freed+0x17a/0x58d lib/debugobjects.c:818

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #3 (&obj_hash[i].lock){-.-.}:
       __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline]
       _raw_spin_lock_irqsave+0x99/0xd0 kernel/locking/spinlock.c:152
       __debug_object_init+0x127/0x1290 lib/debugobjects.c:384
       debug_object_init+0x16/0x20 lib/debugobjects.c:432
       debug_hrtimer_init kernel/time/hrtimer.c:410 [inline]
       debug_init kernel/time/hrtimer.c:458 [inline]
       hrtimer_init+0x97/0x490 kernel/time/hrtimer.c:1308
       init_dl_task_timer+0x1b/0x50 kernel/sched/deadline.c:1057
       __sched_fork+0x2ae/0x590 kernel/sched/core.c:2166
       init_idle+0x75/0x740 kernel/sched/core.c:5382
       sched_init+0xb33/0xc02 kernel/sched/core.c:6065
       start_kernel+0x4be/0xa2b init/main.c:608
       x86_64_start_reservations+0x2e/0x30 arch/x86/kernel/head64.c:472
       x86_64_start_kernel+0x76/0x79 arch/x86/kernel/head64.c:451
       secondary_startup_64+0xa4/0xb0 arch/x86/kernel/head_64.S:243

-> #2 (&rq->lock){-.-.}:
       __raw_spin_lock include/linux/spinlock_api_smp.h:142 [inline]
       _raw_spin_lock+0x2d/0x40 kernel/locking/spinlock.c:144
       rq_lock kernel/sched/sched.h:1127 [inline]
       task_fork_fair+0xb0/0x6d0 kernel/sched/fair.c:9768
       sched_fork+0x443/0xba0 kernel/sched/core.c:2359
       copy_process+0x2585/0x8770 kernel/fork.c:1887
       _do_fork+0x1cb/0x11c0 kernel/fork.c:2216
       kernel_thread+0x34/0x40 kernel/fork.c:2275
       rest_init+0x28/0x372 init/main.c:409
       arch_call_rest_init+0xe/0x1b
       start_kernel+0x9f0/0xa2b init/main.c:745
       x86_64_start_reservations+0x2e/0x30 arch/x86/kernel/head64.c:472
       x86_64_start_kernel+0x76/0x79 arch/x86/kernel/head64.c:451
       secondary_startup_64+0xa4/0xb0 arch/x86/kernel/head_64.S:243

-> #1 (&p->pi_lock){-.-.}:
       __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline]
       _raw_spin_lock_irqsave+0x99/0xd0 kernel/locking/spinlock.c:152
       try_to_wake_up+0xd2/0x12e0 kernel/sched/core.c:1965
       wake_up_process+0x10/0x20 kernel/sched/core.c:2129
       __up.isra.1+0x1c0/0x2a0 kernel/locking/semaphore.c:262
       up+0x13c/0x1c0 kernel/locking/semaphore.c:187
       __up_console_sem+0xbe/0x1b0 kernel/printk/printk.c:236
       console_unlock+0x80c/0x1190 kernel/printk/printk.c:2432
       vprintk_emit+0x391/0x990 kernel/printk/printk.c:1922
       vprintk_default+0x28/0x30 kernel/printk/printk.c:1964
       vprintk_func+0x7e/0x181 kernel/printk/printk_safe.c:398
       printk+0xa7/0xcf kernel/printk/printk.c:1997
       fill_kobj_path lib/kobject.c:151 [inline]
       kobject_get_path.cold.8+0x38/0x47 lib/kobject.c:174
       kobject_uevent_env+0x314/0x101e lib/kobject_uevent.c:519
       call_crda net/wireless/reg.c:556 [inline]
       reg_query_database+0x283/0x400 net/wireless/reg.c:1104
       reg_process_hint_core net/wireless/reg.c:2339 [inline]
       reg_process_hint+0x189/0xec0 net/wireless/reg.c:2677
       reg_process_pending_hints net/wireless/reg.c:2767 [inline]
       reg_todo+0x49a/0xc20 net/wireless/reg.c:2844
       process_one_work+0xc8b/0x1c40 kernel/workqueue.c:2153
       worker_thread+0x17f/0x1390 kernel/workqueue.c:2296
       kthread+0x35a/0x440 kernel/kthread.c:246
       ret_from_fork+0x3a/0x50 arch/x86/entry/entry_64.S:352

-> #0 ((console_sem).lock){-.-.}:
       lock_acquire+0x1ed/0x520 kernel/locking/lockdep.c:3845
       __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline]
       _raw_spin_lock_irqsave+0x99/0xd0 kernel/locking/spinlock.c:152
       down_trylock+0x13/0x70 kernel/locking/semaphore.c:136
       __down_trylock_console_sem+0xae/0x1f0 kernel/printk/printk.c:219
       console_trylock+0x15/0xa0 kernel/printk/printk.c:2247
       console_trylock_spinning kernel/printk/printk.c:1653 [inline]
       vprintk_emit+0x372/0x990 kernel/printk/printk.c:1921
       vprintk_default+0x28/0x30 kernel/printk/printk.c:1964
       vprintk_func+0x7e/0x181 kernel/printk/printk_safe.c:398
       printk+0xa7/0xcf kernel/printk/printk.c:1997
       __warn_printk+0x8c/0xe0 kernel/panic.c:594
       debug_print_object+0x16a/0x210 lib/debugobjects.c:326
       __debug_check_no_obj_freed lib/debugobjects.c:786 [inline]
       debug_check_no_obj_freed+0x3ae/0x58d lib/debugobjects.c:818
       kmem_cache_free+0x202/0x290 mm/slab.c:3759
       free_task_struct kernel/fork.c:163 [inline]
       free_task+0x16e/0x1f0 kernel/fork.c:457
       __put_task_struct+0x2e6/0x620 kernel/fork.c:730
       put_task_struct include/linux/sched/task.h:96 [inline]
       finish_task_switch+0x66b/0x920 kernel/sched/core.c:2715
       context_switch kernel/sched/core.c:2834 [inline]
       __schedule+0x8d7/0x21d0 kernel/sched/core.c:3480
       preempt_schedule_common+0x1f/0xe0 kernel/sched/core.c:3604
       preempt_schedule+0x4d/0x60 kernel/sched/core.c:3630
       ___preempt_schedule+0x16/0x18
       __raw_spin_unlock include/linux/spinlock_api_smp.h:152 [inline]
       _raw_spin_unlock+0x3f/0x50 kernel/locking/spinlock.c:176
       spin_unlock include/linux/spinlock.h:369 [inline]
       zap_pte_range mm/memory.c:1148 [inline]
       zap_pmd_range mm/memory.c:1193 [inline]
       zap_pud_range mm/memory.c:1222 [inline]
       zap_p4d_range mm/memory.c:1243 [inline]
       unmap_page_range+0x18f7/0x2930 mm/memory.c:1264
       unmap_single_vma+0x19b/0x310 mm/memory.c:1309
       unmap_vmas+0x125/0x200 mm/memory.c:1339
       exit_mmap+0x2be/0x590 mm/mmap.c:3145
       __mmput kernel/fork.c:1045 [inline]
       mmput+0x247/0x610 kernel/fork.c:1066
       exec_mmap fs/exec.c:1043 [inline]
       flush_old_exec+0xb91/0x21b0 fs/exec.c:1276
       load_elf_binary+0xa39/0x5620 fs/binfmt_elf.c:869
       search_binary_handler+0x17d/0x570 fs/exec.c:1653
       exec_binprm fs/exec.c:1695 [inline]
       __do_execve_file.isra.33+0x1661/0x25d0 fs/exec.c:1819
       do_execveat_common fs/exec.c:1866 [inline]
       do_execve fs/exec.c:1883 [inline]
       __do_sys_execve fs/exec.c:1964 [inline]
       __se_sys_execve fs/exec.c:1959 [inline]
       __x64_sys_execve+0x8f/0xc0 fs/exec.c:1959
       do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
       entry_SYSCALL_64_after_hwframe+0x49/0xbe

other info that might help us debug this:

Chain exists of:
  (console_sem).lock --> &rq->lock --> &obj_hash[i].lock

 Possible unsafe locking scenario:

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

 *** DEADLOCK ***

2 locks held by udevd/32202:
 #0: 0000000010f1e007 (&sig->cred_guard_mutex){+.+.}, at: prepare_bprm_creds+0x53/0x120 fs/exec.c:1404
 #1: 00000000dc7dcbd1 (&obj_hash[i].lock){-.-.}, at: __debug_check_no_obj_freed lib/debugobjects.c:777 [inline]
 #1: 00000000dc7dcbd1 (&obj_hash[i].lock){-.-.}, at: debug_check_no_obj_freed+0x17a/0x58d lib/debugobjects.c:818

stack backtrace:
CPU: 1 PID: 32202 Comm: udevd Not tainted 4.19.0-rc8-next-20181016+ #95
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0x244/0x39d lib/dump_stack.c:113
 print_circular_bug.isra.35.cold.54+0x1bd/0x27d kernel/locking/lockdep.c:1222
 check_prev_add kernel/locking/lockdep.c:1864 [inline]
 check_prevs_add kernel/locking/lockdep.c:1977 [inline]
 validate_chain kernel/locking/lockdep.c:2348 [inline]
 __lock_acquire+0x3399/0x4c20 kernel/locking/lockdep.c:3342
 lock_acquire+0x1ed/0x520 kernel/locking/lockdep.c:3845
 __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline]
 _raw_spin_lock_irqsave+0x99/0xd0 kernel/locking/spinlock.c:152
 down_trylock+0x13/0x70 kernel/locking/semaphore.c:136
 __down_trylock_console_sem+0xae/0x1f0 kernel/printk/printk.c:219
 console_trylock+0x15/0xa0 kernel/printk/printk.c:2247
 console_trylock_spinning kernel/printk/printk.c:1653 [inline]
 vprintk_emit+0x372/0x990 kernel/printk/printk.c:1921
 vprintk_default+0x28/0x30 kernel/printk/printk.c:1964
 vprintk_func+0x7e/0x181 kernel/printk/printk_safe.c:398
 printk+0xa7/0xcf kernel/printk/printk.c:1997
 __warn_printk+0x8c/0xe0 kernel/panic.c:594
 debug_print_object+0x16a/0x210 lib/debugobjects.c:326
 __debug_check_no_obj_freed lib/debugobjects.c:786 [inline]
 debug_check_no_obj_freed+0x3ae/0x58d lib/debugobjects.c:818
 kmem_cache_free+0x202/0x290 mm/slab.c:3759
 free_task_struct kernel/fork.c:163 [inline]
 free_task+0x16e/0x1f0 kernel/fork.c:457
 __put_task_struct+0x2e6/0x620 kernel/fork.c:730
 put_task_struct include/linux/sched/task.h:96 [inline]
 finish_task_switch+0x66b/0x920 kernel/sched/core.c:2715
 context_switch kernel/sched/core.c:2834 [inline]
 __schedule+0x8d7/0x21d0 kernel/sched/core.c:3480
 preempt_schedule_common+0x1f/0xe0 kernel/sched/core.c:3604
 preempt_schedule+0x4d/0x60 kernel/sched/core.c:3630
 ___preempt_schedule+0x16/0x18
 __raw_spin_unlock include/linux/spinlock_api_smp.h:152 [inline]
 _raw_spin_unlock+0x3f/0x50 kernel/locking/spinlock.c:176
 spin_unlock include/linux/spinlock.h:369 [inline]
 zap_pte_range mm/memory.c:1148 [inline]
 zap_pmd_range mm/memory.c:1193 [inline]
 zap_pud_range mm/memory.c:1222 [inline]
 zap_p4d_range mm/memory.c:1243 [inline]
 unmap_page_range+0x18f7/0x2930 mm/memory.c:1264
 unmap_single_vma+0x19b/0x310 mm/memory.c:1309
 unmap_vmas+0x125/0x200 mm/memory.c:1339
 exit_mmap+0x2be/0x590 mm/mmap.c:3145
 __mmput kernel/fork.c:1045 [inline]
 mmput+0x247/0x610 kernel/fork.c:1066
 exec_mmap fs/exec.c:1043 [inline]
 flush_old_exec+0xb91/0x21b0 fs/exec.c:1276
 ? __sanitizer_cov_trac
Lost 51 message(s)!
Shutting down cpus with NMI
Kernel Offset: disabled
Rebooting in 86400 seconds..