When trying to interact with a emergency shell, this bug brights trouble
by dumping endless status message to console
On 12/25/2017 01:31 PM, piliu wrote:
> Hi,
>
> When debugging with a shell, manager_status_printf() always prints "A
> start job...". After tracing the systemd's code, I found in that
> function, the cond "if (type == STATUS_TYPE_EPHEMERAL && m &&
> m->n_on_console > 0)" does not meet.
>
> With a debugging patch, I got the following message, which indicates
> that there is a reference count bug with n_on_console.1
> The debugging message:
> Manager:0x55e55d91d110, unit: dracut pre-pivot and cleanup hook
> n_on_console++, >1
> service_set_state Manager:0x55e55d91d110, unit: dracut pre-pivot and
> cleanup hook n_on_console--, >0
> Manager:0x55e55d91d110, unit: Kdump Vmcore Save Service n_on_console++, >1
> Manager:0x55e55d91d110, unit: Kdump Vmcore Save Service n_on_console--, >0
> Manager:0x55e55d91d110, unit: dracut pre-pivot and cleanup hook
> n_on_console--, >-1
> Manager:0x55e55d91d110, unit: Kdump Emergency n_on_console++, >0
> Manager:0x55e55d91d110, unit: Kdump Emergency n_on_console--, >-1
> Manager:0x55e55d91d110, unit: Kdump Error Handler n_on_console++, >0
>
> Where you can see "dracut pre-pivot and cleanup hook" dec the refcnt
> twice. (Note: n_on_console is declared as unsigned, so here the negative
> value reflects the underflow.)
>
> Thanks and regards,
> Pingfan
>
> --- The patch I used ---
> diff --git a/src/core/service.c b/src/core/service.c
> index ceed1cc..9ea8ecd 100644
> --- a/src/core/service.c
> +++ b/src/core/service.c
> @@ -868,6 +868,8 @@ static void service_set_state(Service *s,
> ServiceState state) {
> Manager *m = UNIT(s)->manager;
>
> m->n_on_console --;
> + log_debug("service_set_state Manager:0x%lx,
> unit: %s n_on_console--, >%d\n",
> + (unsigned
> long)m,unit_description(UNIT(s)),m->n_on_console);
> if (m->n_on_console == 0)
> /* unset no_console_output flag, since
> the console is free */
> m->no_console_output = false;
> diff --git a/src/core/unit.c b/src/core/unit.c
> index 8c0fde8..6c1f21f 100644
> --- a/src/core/unit.c
> +++ b/src/core/unit.c
> @@ -1827,12 +1827,16 @@ void unit_notify(Unit *u, UnitActiveState os,
> UnitActiveState ns, bool reload_su
> if (ec && exec_context_may_touch_console(ec)) {
> if (UNIT_IS_INACTIVE_OR_FAILED(ns)) {
> m->n_on_console --;
> -
> + log_debug("Manager:0x%lx, unit: %s
> n_on_console--, >%d\n",
> + (unsigned long)m,
> unit_description(u),m->n_on_console);
> if (m->n_on_console == 0)
> /* unset no_console_output
> flag, since the console is free */
> m->no_console_output = false;
> - } else
> + } else{
> m->n_on_console ++;
> + log_debug("Manager:0x%lx, unit: %s
> n_on_console++, >%d\n",
> + (unsigned long)m,
> unit_description(u),m->n_on_console);
> + }
> }
> }
>
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