Bug#856985: systemd: Uninstalling systemd-cron hangs/crashes systemd

[Andreas Bombe]

For the record, my bug appears to have been reported before as #776863.

I have generated a more complete backtrace from the same core:

[New LWP 2615]
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".
Core was generated by `init -z       '.
Program terminated with signal SIGABRT, Aborted.
#0  0x00007fc21779775b in raise (sig=6) at ../nptl/sysdeps/unix/sysv/linux/pt-raise.c:37
#0  0x00007fc21779775b in raise (sig=6) at ../nptl/sysdeps/unix/sysv/linux/pt-raise.c:37
        resultvar = 0
        pid = <optimized out>
#1  0x00007fc217bed4a8 in crash.lto_priv.235 (sig=6) at ../src/core/main.c:158
        rl = {rlim_cur = 18446744073709551615, rlim_max = 18446744073709551615}
        sa = {__sigaction_handler = {sa_handler = 0x0, sa_sigaction = 0x0}, sa_mask = {__val = {0 <repeats 16 times>}}, sa_flags = 0, sa_restorer = 0x0}
        __func__ = "crash"
        __PRETTY_FUNCTION__ = "crash"
#2  <signal handler called>
No locals.
#3  0x00007fc217412067 in __GI_raise (sig=sig at entry=6) at ../nptl/sysdeps/unix/sysv/linux/raise.c:56
        resultvar = 0
        pid = 1
        selftid = 1
#4  0x00007fc217413448 in __GI_abort () at abort.c:89
        save_stage = 2
        act = {__sigaction_handler = {sa_handler = 0x0, sa_sigaction = 0x0}, sa_mask = {__val = {0, 0, 0, 140723367238544, 8470013455670654208, 140471598453408, 140471599596034, 140471599626432, 2, 0, 140471599487084, 1312, 140471599167644, 140471602020864, 140471606932912, 0}}, sa_flags = 406101440, sa_restorer = 0x7fc2183b7590}
        sigs = {__val = {32, 0 <repeats 15 times>}}
#5  0x00007fc217c95ec2 in log_assert_failed (text=text at entry=0x7fc217cbef00 "s->exec_command[SERVICE_EXEC_START]", file=file at entry=0x7fc217cb8202 "../src/core/service.c", line=line at entry=1312, func=func at entry=0x7fc217cbf8c0 <__PRETTY_FUNCTION__.15381> "service_enter_start") at ../src/shared/log.c:709
No locals.
#6  0x00007fc217c65c0f in service_enter_start (s=s at entry=0x7fc218349dc0) at ../src/core/service.c:1312
        c = <optimized out>
        pid = 32706
        r = <optimized out>
        __PRETTY_FUNCTION__ = "service_enter_start"
        __func__ = "service_enter_start"
#7  0x00007fc217c67d41 in service_sigchld_event.lto_priv.376 (u=0x7fc218349dc0, pid=<optimized out>, code=<optimized out>, status=0) at ../src/core/service.c:2337
        f = SERVICE_SUCCESS
        __PRETTY_FUNCTION__ = "service_sigchld_event"
        __func__ = "service_sigchld_event"
#8  0x00007fc217c9ab87 in manager_dispatch_sigchld (m=0x7fc2182d9380) at ../src/core/manager.c:1639
        name = 0x7fc2182ea490 "systemctl"
        u = <optimized out>
        si = {si_signo = 17, si_errno = 0, si_code = 1, _sifields = {_pad = {2599, 0 <repeats 27 times>}, _kill = {si_pid = 2599, si_uid = 0}, _timer = {si_tid = 2599, si_overrun = 0, si_sigval = {sival_int = 0, sival_ptr = 0x0}}, _rt = {si_pid = 2599, si_uid = 0, si_sigval = {sival_int = 0, sival_ptr = 0x0}}, _sigchld = {si_pid = 2599, si_uid = 0, si_status = 0, si_utime = 0, si_stime = 0}, _sigfault = {si_addr = 0xa27, si_addr_lsb = 0}, _sigpoll = {si_band = 2599, si_fd = 0}, _sigsys = {_call_addr = 0xa27, _syscall = 0, _arch = 0}}}
        __PRETTY_FUNCTION__ = "manager_dispatch_sigchld"
        __func__ = "manager_dispatch_sigchld"
#9  0x00007fc217c9c645 in manager_dispatch_signal_fd.lto_priv.926 (source=0x1, fd=1, revents=6, userdata=0x7fc2182d9380) at ../src/core/manager.c:1890
        sfsi = {ssi_signo = 17, ssi_errno = 0, ssi_code = 1, ssi_pid = 2599, ssi_uid = 0, ssi_fd = 0, ssi_tid = 0, ssi_band = 0, ssi_overrun = 0, ssi_trapno = 0, ssi_status = 0, ssi_int = 0, ssi_ptr = 0, ssi_utime = 0, ssi_stime = 0, ssi_addr = 0, __pad = '\000' <repeats 47 times>}
        __PRETTY_FUNCTION__ = "manager_dispatch_signal_fd"
        __func__ = "manager_dispatch_signal_fd"
#10 0x00007fc217bf10b0 in source_dispatch (s=0x7fc2182d9a50) at ../src/libsystemd/sd-event/sd-event.c:2016
        __PRETTY_FUNCTION__ = "source_dispatch"
        __func__ = "source_dispatch"
#11 0x00007fc217bf22ff in sd_event_run (e=0x7fc2182d81a0, timeout=<optimized out>) at ../src/libsystemd/sd-event/sd-event.c:2314
        ev_queue = <optimized out>
        ev_queue_max = <optimized out>
        p = <optimized out>
        r = 0
        i = <optimized out>
        m = 3
        timedout = false
        __PRETTY_FUNCTION__ = "sd_event_run"
#12 0x00007fc217c9b951 in manager_loop (m=0x7fc2182d9380) at ../src/core/manager.c:2009
        wait_usec = 1
        rl = {interval = 1000000, begin = 838679736, burst = 50000, num = 7}
        __PRETTY_FUNCTION__ = "manager_loop"
        __func__ = "manager_loop"
#13 0x00007fc217be9a56 in main (argc=3, argv=<optimized out>) at ../src/core/main.c:1748
        m = 0x7fc2182d9380
        r = <optimized out>
        retval = 1
        before_startup = <optimized out>
        after_startup = <optimized out>
        timespan = "s\302x\356.cx\204\221U_\025J=G\363BE\325\354/cx\204\060cx\204\221x\251ݹ\373\062\000\362?\355s\240sU\241\063S\247\273\313\333\343\370D\366H\023\067|h%\332\f\026\211"
        fds = 0x0
        reexecute = false
        shutdown_verb = 0x0
        initrd_timestamp = {realtime = 0, monotonic = 0}
        userspace_timestamp = {realtime = 1488663133807319, monotonic = 5468359}
        kernel_timestamp = {realtime = 0, monotonic = 0}
        security_start_timestamp = {realtime = 0, monotonic = 0}
        security_finish_timestamp = {realtime = 0, monotonic = 0}
        systemd = "systemd"
        skip_setup = <optimized out>
        j = <optimized out>
        loaded_policy = <optimized out>
        arm_reboot_watchdog = false
        queue_default_job = true
        empty_etc = false
        switch_root_dir = 0x0
        switch_root_init = 0x0
        __func__ = "main"
        __PRETTY_FUNCTION__ = "main"