ThreadSanitizer: lock-order-inversion in pthread_mutex_lock

Job #1621539 failed for cae34f75 on v9.16:

WARNING: ThreadSanitizer: lock-order-inversion (potential deadlock) 
  Cycle in lock order graph: M1 (0x000000000000) => M2 (0x000000000000) => M3 (0x000000000000) => M1

  Mutex M2 acquired here while holding mutex M1 in thread T1:
    #0 pthread_mutex_lock <null>
    #1 dns_view_find lib/dns/view.c:1040
    #2 dbfind_name lib/dns/adb.c:3833
    #3 dns_adb_createfind lib/dns/adb.c:3198
    #4 findname lib/dns/resolver.c:3564
    #5 fctx_getaddresses lib/dns/resolver.c:3875
    #6 fctx_try lib/dns/resolver.c:4264
    #7 fctx_timeout lib/dns/resolver.c:4711
    #8 dispatch lib/isc/task.c:1153
    #9 run lib/isc/task.c:1345
    #10 isc__trampoline_run lib/isc/trampoline.c:191
    #11 <null> <null>

  Mutex M1 previously acquired by the same thread here:
    #0 pthread_mutex_lock <null>
    #1 find_name_and_lock lib/dns/adb.c:2117
    #2 dns_adb_createfind lib/dns/adb.c:3085
    #3 findname lib/dns/resolver.c:3564
    #4 fctx_getaddresses lib/dns/resolver.c:3875
    #5 fctx_try lib/dns/resolver.c:4264
    #6 fctx_timeout lib/dns/resolver.c:4711
    #7 dispatch lib/isc/task.c:1153
    #8 run lib/isc/task.c:1345
    #9 isc__trampoline_run lib/isc/trampoline.c:191
    #10 <null> <null>

  Mutex M3 acquired here while holding mutex M2 in thread T2:
    #0 pthread_mutex_lock <null>
    #1 dns_zone_flush lib/dns/zone.c:11441
    #2 flush lib/dns/zt.c:215
    #3 dns_zt_apply lib/dns/zt.c:537
    #4 zt_destroy lib/dns/zt.c:221
    #5 zt_flushanddetach lib/dns/zt.c:243
    #6 dns_zt_flushanddetach lib/dns/zt.c:249
    #7 view_flushanddetach lib/dns/view.c:645
    #8 dns_view_flushanddetach lib/dns/view.c:687
    #9 shutdown_server server.c:9873
    #10 dispatch lib/isc/task.c:1153
    #11 run lib/isc/task.c:1345
    #12 isc__trampoline_run lib/isc/trampoline.c:191
    #13 <null> <null>

  Mutex M2 previously acquired by the same thread here:
    #0 pthread_mutex_lock <null>
    #1 view_flushanddetach lib/dns/view.c:642
    #2 dns_view_flushanddetach lib/dns/view.c:687
    #3 shutdown_server server.c:9873
    #4 dispatch lib/isc/task.c:1153
    #5 run lib/isc/task.c:1345
    #6 isc__trampoline_run lib/isc/trampoline.c:191
    #7 <null> <null>

  Mutex M1 acquired here while holding mutex M3 in thread T3:
    #0 pthread_mutex_lock <null>
    #1 violate_locking_hierarchy lib/dns/adb.c:1279
    #2 dns_adb_cancelfind lib/dns/adb.c:3457
    #3 notify_cancel lib/dns/zone.c:11796
    #4 zone_shutdown lib/dns/zone.c:14532
    #5 dispatch lib/isc/task.c:1153
    #6 run lib/isc/task.c:1345
    #7 isc__trampoline_run lib/isc/trampoline.c:191
    #8 <null> <null>

  Mutex M3 previously acquired by the same thread here:
    #0 pthread_mutex_lock <null>
    #1 zone_shutdown lib/dns/zone.c:14503
    #2 dispatch lib/isc/task.c:1153
    #3 run lib/isc/task.c:1345
    #4 isc__trampoline_run lib/isc/trampoline.c:191
    #5 <null> <null>

  Thread T1 (running) created by main thread at:
    #0 pthread_create <null>
    #1 isc_thread_create lib/isc/pthreads/thread.c:79
    #2 isc_taskmgr_create lib/isc/task.c:1435
    #3 create_managers main.c:928
    #4 setup main.c:1269
    #5 main main.c:1572

  Thread T2 (running) created by main thread at:
    #0 pthread_create <null>
    #1 isc_thread_create lib/isc/pthreads/thread.c:79
    #2 isc_taskmgr_create lib/isc/task.c:1435
    #3 create_managers main.c:928
    #4 setup main.c:1269
    #5 main main.c:1572

  Thread T3 (running) created by main thread at:
    #0 pthread_create <null>
    #1 isc_thread_create lib/isc/pthreads/thread.c:79
    #2 isc_taskmgr_create lib/isc/task.c:1435
    #3 create_managers main.c:928
    #4 setup main.c:1269
    #5 main main.c:1572

SUMMARY: ThreadSanitizer: lock-order-inversion (potential deadlock) in pthread_mutex_lock