======================================
| [ 44.888256][ C1] ret_from_fork_asm (arch/x86/entry/entry_64.S:256) 
| [   44.888460][    C1]
| [   44.888556][    C1]
| [   44.888556][    C1] stack backtrace:
[   44.889176][    C1] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014
[   44.889720][    C1] Call Trace:
[   44.889868][    C1]  <TASK>
[ 44.889991][ C1] dump_stack_lvl (lib/dump_stack.c:117) 
[ 44.890201][ C1] print_irq_inversion_bug.part.0 (kernel/locking/lockdep.c:4024) 
[ 44.890457][ C1] ? kernel_text_address (kernel/extable.c:99) 
[ 44.890671][ C1] ? __pfx_print_irq_inversion_bug.part.0 (kernel/locking/lockdep.c:4024) 
[ 44.891193][ C1] ? __pfx_usage_skip (kernel/locking/lockdep.c:2264) 
[ 44.891399][ C1] ? __pfx_usage_match (kernel/locking/lockdep.c:2256) 
[ 44.891590][ C1] ? arch_stack_walk (arch/x86/kernel/stacktrace.c:24) 
[ 44.891804][ C1] mark_lock_irq (kernel/locking/lockdep.c:4244) 
[ 44.892013][ C1] ? ret_from_fork_asm (arch/x86/entry/entry_64.S:256) 
[ 44.892217][ C1] ? __pfx_mark_lock_irq (kernel/locking/lockdep.c:4207) 
[ 44.892422][ C1] ? __pfx_stack_trace_save (kernel/stacktrace.c:114) 
[ 44.892628][ C1] ? add_chain_cache (kernel/locking/lockdep.c:3730) 
[ 44.892835][ C1] ? save_trace (kernel/locking/lockdep.c:586) 
[ 44.893166][ C1] mark_lock (kernel/locking/lockdep.c:4678) 
[ 44.893342][ C1] mark_usage (kernel/locking/lockdep.c:4567) 
[ 44.893501][ C1] __lock_acquire (kernel/locking/lockdep.c:5091) 
[ 44.893715][ C1] ? __lock_acquire (kernel/locking/lockdep.c:5137) 
[ 44.894045][ C1] ? __pfx_br_forward_delay_timer_expired (net/bridge/br_stp_timer.c:80) bridge
[ 44.894425][ C1] lock_acquire.part.0 (kernel/locking/lockdep.c:467 kernel/locking/lockdep.c:5756) 
[ 44.894631][ C1] ? br_forward_delay_timer_expired (net/bridge/br_stp_timer.c:87) bridge
[ 44.894956][ C1] ? __pfx_lock_acquire.part.0 (kernel/locking/lockdep.c:5719) 
[ 44.895285][ C1] ? trace_lock_acquire (./include/trace/events/lock.h:24 (discriminator 52)) 
[ 44.895493][ C1] ? br_forward_delay_timer_expired (net/bridge/br_stp_timer.c:87) bridge
[ 44.895819][ C1] ? lock_acquire (kernel/locking/lockdep.c:5727) 
[ 44.896156][ C1] ? br_forward_delay_timer_expired (net/bridge/br_stp_timer.c:87) bridge
[ 44.896611][ C1] _raw_spin_lock (./include/linux/spinlock_api_smp.h:134 kernel/locking/spinlock.c:154) 
[ 44.896815][ C1] ? br_forward_delay_timer_expired (net/bridge/br_stp_timer.c:87) bridge
[ 44.897276][ C1] br_forward_delay_timer_expired (net/bridge/br_stp_timer.c:87) bridge
[ 44.897605][ C1] ? __pfx_br_forward_delay_timer_expired (net/bridge/br_stp_timer.c:80) bridge
[ 44.897978][ C1] call_timer_fn (kernel/time/timer.c:1793) 
[ 44.898315][ C1] ? call_timer_fn (./include/linux/lockdep.h:31 kernel/time/timer.c:1783) 
[ 44.898521][ C1] ? call_timer_fn (./include/linux/lockdep.h:31 kernel/time/timer.c:1783) 
[ 44.898858][ C1] ? __pfx_call_timer_fn (kernel/time/timer.c:1770) 
[ 44.899059][ C1] ? mark_lock (kernel/locking/lockdep.c:4656 (discriminator 3)) 
[ 44.899220][ C1] __run_timers (kernel/time/timer.c:1845 kernel/time/timer.c:2418) 
[ 44.899435][ C1] ? __pfx_br_forward_delay_timer_expired (net/bridge/br_stp_timer.c:80) bridge
[ 44.899944][ C1] ? __pfx___run_timers (kernel/time/timer.c:2389) 
[ 44.900283][ C1] ? do_raw_spin_lock (./arch/x86/include/asm/atomic.h:115 ./include/linux/atomic/atomic-arch-fallback.h:2170 ./include/linux/atomic/atomic-instrumented.h:1302 ./include/asm-generic/qspinlock.h:111 kernel/locking/spinlock_debug.c:116) 
[ 44.900486][ C1] ? __pfx_do_raw_spin_lock (kernel/locking/spinlock_debug.c:114) 
[ 44.900691][ C1] ? lock_acquire (kernel/locking/lockdep.c:5727) 
[ 44.901024][ C1] ? run_timer_softirq (kernel/time/timer.c:2429 kernel/time/timer.c:2422 kernel/time/timer.c:2438 kernel/time/timer.c:2448) 
[ 44.901253][ C1] run_timer_softirq (kernel/time/timer.c:2430 kernel/time/timer.c:2422 kernel/time/timer.c:2438 kernel/time/timer.c:2448) 
[ 44.901471][ C1] __do_softirq (kernel/softirq.c:554) 
[ 44.901675][ C1] ? __pfx_run_ksoftirqd (kernel/softirq.c:917) 
[ 44.901881][ C1] run_ksoftirqd (kernel/softirq.c:411 kernel/softirq.c:925 kernel/softirq.c:916) 
[ 44.902216][ C1] smpboot_thread_fn (kernel/smpboot.c:164 (discriminator 3)) 
[ 44.902548][ C1] ? __pfx_smpboot_thread_fn (kernel/smpboot.c:107) 
[ 44.902756][ C1] ? __pfx_smpboot_thread_fn (kernel/smpboot.c:107) 
[ 44.902961][ C1] kthread (kernel/kthread.c:388) 
[ 44.903245][ C1] ? __pfx_kthread (kernel/kthread.c:341) 
[ 44.903450][ C1] ret_from_fork (arch/x86/kernel/process.c:147) 
[ 44.903652][ C1] ? __pfx_kthread (kernel/kthread.c:341) 


Finger prints:
ret_from_fork_asm:dump_stack_lvl:mark_lock_irq:mark_lock