This is in OBS with gdb-12.1 based package, with patches added to reflect gdb-12-branch:
...
start^M
Temporary breakpoint 2 at 0x10000760: file /home/abuild/rpmbuild/BUILD/gdb-12.1/gdb/testsuite/gdb.base/run-control-while-bg-execution.c, line 30.^M
Starting program: /home/abuild/rpmbuild/BUILD/gdb-12.1/build-ppc64le-suse-linux/gdb/testsuite.unix.-m64.-fno-PIE.-no-pie/outputs/gdb.base/run-control-while-bg-execution/run-control-while-bg-execution ^M
../../gdb/displaced-stepping.c:53: internal-error: prepare: Assertion `buf.current_thread != thread' failed.^M
A problem internal to GDB has been detected,^M
further debugging may prove unreliable.^M
----- Backtrace -----^M
FAIL: gdb.base/run-control-while-bg-execution.exp: action1=none: action2=start: start (GDB internal error)
...

Backtrace:
...
0x10fc38143 gdb_internal_backtrace_1
        ../../gdb/bt-utils.c:122
0x10fc38143 gdb_internal_backtrace()
        ../../gdb/bt-utils.c:168
0x110193b73 internal_vproblem
        ../../gdb/utils.c:394
0x110193daf internal_verror(char const*, int, char const*, char*)
        ../../gdb/utils.c:471
0x1103d656f internal_error(char const*, int, char const*, ...)
        ../../gdbsupport/errors.cc:55
0x10fd0dcc3 displaced_step_buffers::prepare(thread_info*, unsigned long&)
        ../../gdb/displaced-stepping.c:53
0x10ff51743 ppc_linux_displaced_step_prepare
        ../../gdb/ppc-linux-tdep.c:2040
0x10fba6c03 gdbarch_displaced_step_prepare(gdbarch*, thread_info*, unsigned long&)
        ../../gdb/gdbarch.c:4048
0x10fe38ef7 displaced_step_prepare_throw
        ../../gdb/infrun.c:1675
0x10fe38ef7 displaced_step_prepare
        ../../gdb/infrun.c:1726
0x10fe38ef7 resume_1
        ../../gdb/infrun.c:2377
0x10fe38ef7 resume
        ../../gdb/infrun.c:2569
0x10fe398cf keep_going_pass_signal
        ../../gdb/infrun.c:8077
0x10fe3cc97 process_event_stop_test
        ../../gdb/infrun.c:6966
0x10fe3f7bf handle_signal_stop
        ../../gdb/infrun.c:6420
0x10fe40ebf handle_inferior_event
        ../../gdb/infrun.c:5681
0x10fe420cf fetch_inferior_event()
        ../../gdb/infrun.c:4085
0x10fe15df3 inferior_event_handler(inferior_event_type)
        ../../gdb/inf-loop.c:41
0x10fe6da9b handle_target_event
        ../../gdb/linux-nat.c:4154
0x1103d666f handle_file_event
        ../../gdbsupport/event-loop.cc:574
0x1103d71c3 gdb_wait_for_event
        ../../gdbsupport/event-loop.cc:700
0x1103d7467 gdb_do_one_event()
        ../../gdbsupport/event-loop.cc:212
0x10fea5323 start_event_loop
        ../../gdb/main.c:421
0x10fea5323 captured_command_loop
        ../../gdb/main.c:481
0x10fea73fb captured_main
        ../../gdb/main.c:1356
0x10fea7487 gdb_main(captured_main_args*)
        ../../gdb/main.c:1371
0x10fb0da43 main
        ../../gdb/gdb.c:32
...