TSAN error in dispatch.c accessing disp->portentry

Job #1237048 failed for 33ea90f7:

WARNING: ThreadSanitizer: data race 
  Write of size 8 at 0x000000000001 by thread T1 (mutexes: write M1):
    #0 deref_portentry lib/dns/dispatch.c:630
    #1 deactivate_dispsocket lib/dns/dispatch.c:861
    #2 udp_recv lib/dns/dispatch.c:1105
    #3 udp_exrecv lib/dns/dispatch.c:1028
    #4 dispatch lib/isc/task.c:1152
    #5 run lib/isc/task.c:1344
    #6 <null> <null>

  Previous read of size 8 at 0x000000000001 by thread T2 (mutexes: write M1, write M2):
    #0 socket_search lib/dns/dispatch.c:661
    #1 get_dispsocket lib/dns/dispatch.c:744
    #2 dns_dispatch_addresponse lib/dns/dispatch.c:3120
    #3 resquery_send lib/dns/resolver.c:2467
    #4 fctx_query lib/dns/resolver.c:2217
    #5 fctx_try lib/dns/resolver.c:4245
    #6 fctx_timeout lib/dns/resolver.c:4570
    #7 dispatch lib/isc/task.c:1152
    #8 run lib/isc/task.c:1344
    #9 <null> <null>

  Location is heap block of size 249 at 0x000000000013 allocated by thread T2:
    #0 malloc <null>
    #1 default_memalloc lib/isc/mem.c:713
    #2 mem_get lib/isc/mem.c:622
    #3 isc__mempool_get lib/isc/mem.c:1775
    #4 get_dispsocket lib/dns/dispatch.c:712
    #5 dns_dispatch_addresponse lib/dns/dispatch.c:3120
    #6 resquery_send lib/dns/resolver.c:2467
    #7 fctx_query lib/dns/resolver.c:2217
    #8 fctx_try lib/dns/resolver.c:4245
    #9 fctx_start lib/dns/resolver.c:4761
    #10 dispatch lib/isc/task.c:1152
    #11 run lib/isc/task.c:1344
    #12 <null> <null>

  Mutex M1 (0x000000000019) created at:
    #0 pthread_mutex_init <null>
    #1 isc__mutex_init pthreads/mutex.c:288
    #2 dispatch_allocate lib/dns/dispatch.c:2358
    #3 dispatch_createudp lib/dns/dispatch.c:2855
    #4 dns_dispatchset_create lib/dns/dispatch.c:3666
    #5 dns_resolver_create lib/dns/resolver.c:10190
    #6 dns_view_createresolver lib/dns/view.c:811
    #7 configure_view bin/named/server.c:4571
    #8 load_configuration bin/named/server.c:9110
    #9 loadconfig bin/named/server.c:10310
    #10 named_server_reconfigcommand bin/named/server.c:10693
    #11 named_control_docommand bin/named/control.c:250
    #12 control_command bin/named/controlconf.c:392
    #13 dispatch lib/isc/task.c:1152
    #14 run lib/isc/task.c:1344
    #15 <null> <null>

  Mutex M2 is already destroyed.

  Thread T1 (running) created by main thread at:
    #0 pthread_create <null>
    #1 isc_thread_create pthreads/thread.c:73
    #2 isc_taskmgr_create lib/isc/task.c:1434
    #3 create_managers bin/named/main.c:915
    #4 setup bin/named/main.c:1223
    #5 main bin/named/main.c:1523

  Thread T2 (running) created by main thread at:
    #0 pthread_create <null>
    #1 isc_thread_create pthreads/thread.c:73
    #2 isc_taskmgr_create lib/isc/task.c:1434
    #3 create_managers bin/named/main.c:915
    #4 setup bin/named/main.c:1223
    #5 main bin/named/main.c:1523

SUMMARY: ThreadSanitizer: data race lib/dns/dispatch.c:630 in deref_portentry