(gdb) bt
#0  0x00000000007b2aa6 in erts_proc_sig_fetch__ (proc=0x7f273abf9168, buffers=0x0, need_unget_buffers=0) at beam/erl_proc_sig_queue.c:1229
#1  0x000000000086d7c6 in erts_proc_sig_fetch (proc=0x7f273abf9168) at beam/erl_proc_sig_queue.h:1894
#2  erts_garbage_collect_nobump (p=p@entry=0x7f273abf9168, need=need@entry=0, objv=0x7f25c1b0ade8, nobj=2, fcalls=4000) at beam/erl_gc.c:900
#3  0x000000000061c9c7 in erts_execute_dirty_system_task (c_p=c_p@entry=0x7f273abf9168) at beam/erl_process.c:11055
#4  0x00000000006cf339 in erts_dirty_process_main (esdp=esdp@entry=0x7f25b8720880) at beam/beam_common.c:202
#5  0x0000000000606368 in sched_dirty_cpu_thread_func (vesdp=0x7f25b8720880) at beam/erl_process.c:8720
#6  0x0000000000a237ec in thr_wrapper (vtwd=0x7ffc5e92e3f0) at pthread/ethread.c:116
#7  0x00007f301a89abaf in start_thread (arg=<optimized out>) at pthread_create.c:434
#8  0x00007f301a92d17c in clone3 () at ../sysdeps/unix/sysv/linux/x86_64/clone3.S:81

(gdb) etp-process-info proc
  Pid: <0.24317.3736>
  State: dirty-running-sys | dirty-active-sys | sig-q | active-sys | nmsig-in-q | active | prq-prio-normal | usr-prio-normal | act-prio-normal

  Flags: dirty-minor-gc force-gc
  Current function: erlang:bif_handle_signals_return/2
  I: #Cp<0x7f2563400260>
  Heap size: 196650
  Old-heap size: 1199557
  Mbuf size: 2312
  Msgq len: 2 (inner=2, outer=0)
  Msgq Flags: handling-sig on-heap
  Parent: <0.22824.81>
  Pointer: (Process*)0x7f273abf9168

(gdb) etp-sigqs proc
Msgq Flags: handling-sig on-heap
--- Inner signal queue (message queue) ---
  [{inet_reply,#Port<0.33357938>,ok,#Ref<0.482064594.4069785604.108568>} @token= undefined @from= #Port<0.33357938> % <== SAVE]

  Message signals: 1
  Non-message signals: 0

--- Middle signal queue ---
  [{tcp_closed,#Port<0.33357938>} @token= undefined @from= #Port<0.33357938>]

  Message signals: 1
  Non-message signals: 0

--- Outer queue ---
  [!MONITOR-DOWN[1]]

  Message signals: 0
  Non-message signals: 1


(gdb) p proc->sig_qs.nmsigs.last
$5 = (ErtsMessage **) 0x7fcfb01c3560
(gdb) p *proc->sig_qs.nmsigs.last
$6 = (ErtsMessage *) 0x0

(gdb) bt
#0  0x00007f301a9100c7 in sched_yield () at ../sysdeps/unix/syscall-template.S:120
#1  0x00000000007bfd15 in erts_thr_yield () at beam/erl_threads.h:2548
#2  erts_proc_lock_failed (p=p@entry=0x7f273abf9168, pixlck=pixlck@entry=0x0, locks=locks@entry=1, old_lflgs=<optimized out>) at beam/erl_process_lock.c:509
#3  0x000000000078af59 in erts_proc_lock__ (pix_lck=<optimized out>, locks=<optimized out>, p=<optimized out>) at beam/erl_process_lock.h:692
#4  erts_proc_lock (locks=<optimized out>, p=<optimized out>) at beam/erl_process_lock.h:954
#5  erts_schedule_proc2port_signal (prt=<optimized out>, caller=<optimized out>, refp=<optimized out>, sigdp=<optimized out>, task_flags=<optimized out>, pthp=<optimized out>, callback=<optimized out>, c_p=<optimized out>) at beam/io.c:1208
#6  erts_schedule_proc2port_signal (c_p=0x7f273abf9168, prt=0x7f25efbc63c0, caller=6254096339, refp=<optimized out>, sigdp=0x7f25b88d8540, task_flags=0, pthp=0x0, callback=0x78b130 <port_sig_unlink_ack>) at beam/io.c:1153
#7  0x0000000000795fb1 in erts_port_unlink_ack (c_p=c_p@entry=0x7f273abf9168, prt=0x7f25efbc63c0, sulnk=sulnk@entry=0x10e41c0) at beam/io.c:2630
#8  0x00000000007b655f in erts_proc_sig_handle_incoming (c_p=c_p@entry=0x7f273abf9168, statep=statep@entry=0x7f256139ac08, redsp=redsp@entry=0x7f256139ac0c, max_reds=3993, local_only=local_only@entry=0) at beam/erl_proc_sig_queue.c:6169
#9  0x00000000007b9aec in erts_internal_dirty_process_handle_signals_1 (A__p=0x192cb20, BIF__ARGS=<optimized out>, A__I=<optimized out>) at beam/erl_proc_sig_queue.c:8307
#10 0x00007f2563400649 in ?? ()
#11 0x0000000000000000 in ?? ()