Walking the stack up one by one only triggers the "PC not saved" when the stack goes into libc:

(gdb) break builtin_id
Breakpoint 1 at 0x139403c: file Python/bltinmodule.c, line 1182.
(gdb) r
Starting program: /home/linux1/cpython/python tester.py
Missing separate debuginfos, use: zypper install glibc-debuginfo-2.22-62.13.2.s390x
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib64/libthread_db.so.1".
[New Thread 0x3fffd2ff910 (LWP 9951)]
[New Thread 0x3fffcaff910 (LWP 9952)]
[New Thread 0x3fff7fff910 (LWP 9953)]
[New Thread 0x3fff77ff910 (LWP 9954)]

Thread 1 "python" hit Breakpoint 1, builtin_id (self=0x3fffdf5c0c8, v=0x14f7690 <small_ints+2256>) at Python/bltinmodule.c:1182
1182        return PyLong_FromVoidPtr(v);
(gdb) thread 2
[Switching to thread 2 (Thread 0x3fffd2ff910 (LWP 9951))]
#0  0x000003fffde8da0a in pthread_cond_timedwait@@GLIBC_2.3.2 () from /lib64/libpthread.so.0
(gdb) up
#1  0x0000000001186a2e in PyCOND_TIMEDWAIT (cond=0x15139b0 <_PyRuntime+1192>, mut=0x15139e0 <_PyRuntime+1240>, us=5000) at Python/condvar.h:90
90          r = pthread_cond_timedwait((cond), (mut), &ts);
(gdb)
#2  0x0000000001186f3a in take_gil (tstate=0x1538620) at Python/ceval_gil.h:208
208             COND_TIMED_WAIT(_PyRuntime.ceval.gil.cond, _PyRuntime.ceval.gil.mutex,
(gdb)
#3  0x00000000011884a6 in _PyEval_EvalFrameDefault (f=0x3fffd844d00, throwflag=0) at Python/ceval.c:980
980                     take_gil(tstate);
(gdb)
#4  0x0000000001187db8 in PyEval_EvalFrameEx (f=0x3fffd844d00, throwflag=0) at Python/ceval.c:536
536         return interp->eval_frame(f, throwflag);
(gdb)
#5  0x0000000001047596 in function_code_fastcall (co=0x3fffdd76640, args=0x3fff8000a98, nargs=1, globals=0x3fffddcff30) at Objects/call.c:283
283         result = PyEval_EvalFrameEx(f,0);
(gdb)
#6  0x0000000001048144 in _PyFunction_FastCallKeywords (func=0x3fffd7d8680, stack=0x3fff8000a90, nargs=1, kwnames=0x0) at Objects/call.c:408
408                 return function_code_fastcall(co, stack, nargs, globals);
(gdb)
#7  0x00000000011a48b6 in call_function (pp_stack=0x3fffd2fb5f8, oparg=1, kwnames=0x0) at Python/ceval.c:4623
4623                x = _PyFunction_FastCallKeywords(func, stack, nargs, kwnames);
(gdb)
#8  0x000000000119c088 in _PyEval_EvalFrameDefault (f=0x3fff80008f0, throwflag=0) at Python/ceval.c:3186
3186                    res = call_function(&sp, oparg + 1, NULL);
(gdb)
#9  0x0000000001187db8 in PyEval_EvalFrameEx (f=0x3fff80008f0, throwflag=0) at Python/ceval.c:536
536         return interp->eval_frame(f, throwflag);
(gdb)
#10 0x0000000001047596 in function_code_fastcall (co=0x3fffda6e580, args=0x3fffd87e980, nargs=1, globals=0x3fffdd717c0) at Objects/call.c:283
283         result = PyEval_EvalFrameEx(f,0);
(gdb)
#11 0x0000000001048144 in _PyFunction_FastCallKeywords (func=0x3fffd7d61b0, stack=0x3fffd87e978, nargs=1, kwnames=0x0) at Objects/call.c:408
408                 return function_code_fastcall(co, stack, nargs, globals);
(gdb)
#12 0x00000000011a48b6 in call_function (pp_stack=0x3fffd2fd1b8, oparg=1, kwnames=0x0) at Python/ceval.c:4623
4623                x = _PyFunction_FastCallKeywords(func, stack, nargs, kwnames);
(gdb)
#13 0x000000000119c088 in _PyEval_EvalFrameDefault (f=0x3fffd87e7f0, throwflag=0) at Python/ceval.c:3186
3186                    res = call_function(&sp, oparg + 1, NULL);
(gdb)
#14 0x0000000001187db8 in PyEval_EvalFrameEx (f=0x3fffd87e7f0, throwflag=0) at Python/ceval.c:536
536         return interp->eval_frame(f, throwflag);
(gdb)
#15 0x0000000001047596 in function_code_fastcall (co=0x3fffda6e340, args=0x3fffd2fed28, nargs=1, globals=0x3fffdd717c0) at Objects/call.c:283
283         result = PyEval_EvalFrameEx(f,0);
(gdb)
#16 0x0000000001047a2e in _PyFunction_FastCallDict (func=0x3fffd7d3f70, args=0x3fffd2fed20, nargs=1, kwargs=0x0) at Objects/call.c:322
322                 return function_code_fastcall(co, args, nargs, globals);
(gdb)
#17 0x00000000010467d6 in _PyObject_FastCallDict (callable=0x3fffd7d3f70, args=0x3fffd2fed20, nargs=1, kwargs=0x0) at Objects/call.c:98
98              return _PyFunction_FastCallDict(callable, args, nargs, kwargs);
(gdb)
#18 0x0000000001049c5c in _PyObject_Call_Prepend (callable=0x3fffd7d3f70, obj=0x3fffdc70650, args=0x3fffdfb9050, kwargs=0x0)
    at Objects/call.c:904
904         result = _PyObject_FastCallDict(callable,
(gdb)
#19 0x0000000001324f02 in method_call (method=0x3fffdeee258, args=0x3fffdfb9050, kwargs=0x0) at Objects/classobject.c:306
306         return _PyObject_Call_Prepend(func, self, args, kwargs);
(gdb)
#20 0x0000000001047396 in PyObject_Call (callable=0x3fffdeee258, args=0x3fffdfb9050, kwargs=0x0) at Objects/call.c:245
245             result = (*call)(callable, args, kwargs);
(gdb)
#21 0x00000000012b91be in t_bootstrap (boot_raw=0x3fffd9fb118) at ./Modules/_threadmodule.c:992
992         res = PyObject_Call(boot->func, boot->args, boot->keyw);
(gdb)
#22 0x000003fffde88b22 in start_thread () from /lib64/libpthread.so.0
(gdb)
#23 0x000003fffdb7164a in thread_start () from /lib64/libc.so.6
(gdb)
PC not saved