assertion error in isc__timer_create(): task != ((void *)0)

Summary

The command host -t soa local. crashed with an assertion error:

#2 0x00007fe590c645ef in isc_assertion_failed (file=file@entry=0x7fe590cb769c "../../../lib/isc/timer.c", line=line@entry=392, type=type@entry=isc_assertiontype_require, cond=cond@entry=0x7fe590cb0103 "task != ((void *)0)") at ../../../lib/isc/assertions.c:52

Ubuntu bug: https://bugs.launchpad.net/ubuntu/+source/bind9/+bug/1797926

BIND version used

1:9.11.4+dfsg-3ubuntu5 in Ubuntu Cosmic 18.10 (https://launchpad.net/ubuntu/+source/bind9/1:9.11.4+dfsg-3ubuntu5)

Steps to reproduce

Unknown, but reporter indicated it was after his computer came back from sleep.

What is the current bug behavior?

The host command failed with an assertion error.

What is the expected correct behavior?

The host command should produce a result, or timeout and fail gracefully.

Relevant logs and/or screenshots

Backtrace:

#0  __GI_raise (sig=sig@entry=6) at ../sysdeps/unix/sysv/linux/raise.c:50
  [Error: raise.c was not found in source tree]
#1  0x00007fe590a44535 in __GI_abort () at abort.c:79
  [Error: abort.c was not found in source tree]
#2  0x00007fe590c645ef in isc_assertion_failed (file=file@entry=0x7fe590cb769c "../../../lib/isc/timer.c", line=line@entry=392, type=type@entry=isc_assertiontype_require, cond=cond@entry=0x7fe590cb0103 "task != ((void *)0)") at ../../../lib/isc/assertions.c:52
  47: void
  48: isc_assertion_failed(const char *file, int line, isc_assertiontype_t type,
  49: 		     const char *cond)
  50: {
  51: 	isc_assertion_failed_cb(file, line, type, cond);
  52: 	abort();
  53: 	/* NOTREACHED */
  54: }
  55: 
  56: /*% Set callback. */
  57: void
#3  0x00007fe590c9245a in isc__timer_create (manager0=0x7fe58d741010, type=<optimized out>, expires=<optimized out>, interval=<optimized out>, task=0x0, action=0x55bcf1af75c0 <connect_timeout>, arg=0x7fe58d74e018, timerp=0x7fe58d74e288) at ../../../lib/isc/timer.c:457
  452: 	timer->index = 0;
  453: 	result = isc_mutex_init(&timer->lock);
  454: 	if (result != ISC_R_SUCCESS) {
  455: 		isc_task_detach(&timer->task);
  456: 		isc_mem_put(manager->mctx, timer, sizeof(*timer));
  457: 		return (result);
  458: 	}
  459: 	ISC_LINK_INIT(timer, link);
  460: 	timer->common.impmagic = TIMER_MAGIC;
  461: 	timer->common.magic = ISCAPI_TIMER_MAGIC;
  462: 	timer->common.methods = (isc_timermethods_t *)&timermethods;
#4  0x000055bcf1aef75a in bringup_timer (query=0x7fe58d74e018, default_timeout=<optimized out>) at ../../../bin/dig/dighost.c:2949
  2944: 	}
  2945: 	debug("have local timeout of %d", local_timeout);
  2946: 	isc_interval_set(&l->interval, local_timeout, 0);
  2947: 	if (query->timer != NULL)
  2948: 		isc_timer_detach(&query->timer);
  2949: 	result = isc_timer_create(timermgr, isc_timertype_once, NULL,
  2950: 				  &l->interval, global_task, connect_timeout,
  2951: 				  query, &query->timer);
  2952: 	check_result(result, "isc_timer_create");
  2953: }
  2954: 
#5  0x000055bcf1af6e22 in send_udp (query=0x7fe58d74e018) at ../../../bin/dig/dighost.c:3135
  3130: 	dig_query_t *next;
  3131: 
  3132: 	debug("send_udp(%p)", query);
  3133: 
  3134: 	l = query->lookup;
  3135: 	bringup_timer(query, UDP_TIMEOUT);
  3136: 	l->current_query = query;
  3137: 	debug("working on lookup %p, query %p", query->lookup, query);
  3138: 	if (!query->recv_made) {
  3139: 		/* XXX Check the sense of this, need assertion? */
  3140: 		query->waiting_connect = ISC_FALSE;
#6  0x000055bcf1af76c5 in connect_timeout (task=<optimized out>, event=<optimized out>) at ../../../bin/dig/dighost.c:3265
  3260: 
  3261: 	if (l->retries > 1) {
  3262: 		if (!l->tcp_mode) {
  3263: 			l->retries--;
  3264: 			debug("resending UDP request to first server");
  3265: 			send_udp(ISC_LIST_HEAD(l->q));
  3266: 		} else {
  3267: 			debug("making new TCP request, %d tries left",
  3268: 			      l->retries);
  3269: 			l->retries--;
  3270: 			requeue_lookup(l, ISC_TRUE);
#7  0x00007fe590c8c439 in dispatch (manager=0x7fe58d73f010) at ../../../lib/isc/task.c:1141
  1136: 							    ISC_MSGSET_TASK,
  1137: 							    ISC_MSG_EXECUTE,
  1138: 							    "execute action"));
  1139: 					if (event->ev_action != NULL) {
  1140: 						UNLOCK(&task->lock);
  1141: 						(event->ev_action)(
  1142: 							(isc_task_t *)task,
  1143: 							event);
  1144: 						LOCK(&task->lock);
  1145: 					}
  1146: 					dispatch_count++;
#8  run (uap=0x7fe58d73f010) at ../../../lib/isc/task.c:1313
  1308: 	isc__taskmgr_t *manager = uap;
  1309: 
  1310: 	XTHREADTRACE(isc_msgcat_get(isc_msgcat, ISC_MSGSET_GENERAL,
  1311: 				    ISC_MSG_STARTING, "starting"));
  1312: 
  1313: 	dispatch(manager);
  1314: 
  1315: 	XTHREADTRACE(isc_msgcat_get(isc_msgcat, ISC_MSGSET_GENERAL,
  1316: 				    ISC_MSG_EXITING, "exiting"));
  1317: 
  1318: #ifdef OPENSSL_LEAKS
#9  0x00007fe590c14164 in start_thread (arg=<optimized out>) at pthread_create.c:486
  [Error: pthread_create.c was not found in source tree]
#10 0x00007fe590b3cdef in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:95
  [Error: clone.S was not found in source tree]

The host call that triggered the assertion was most likely the same one from issue #520 (closed)