TSAN error in 9.16/9.17 forwarding updates

Job #1795733 failed for 2c38ba46:

WARNING: ThreadSanitizer: data race 
  Write of size 8 at 0x000000000001 by thread T1:
    #0 recvmsg <null>
    #1 <null> <null>
    #2 isc__trampoline_run lib/isc/trampoline.c:191
    #3 <null> <null>

  Previous read of size 8 at 0x000000000001 by thread T2:
    #0 memmove <null>
    #1 isc_buffer_copyregion lib/isc/buffer.c:530
    #2 dns_zone_forwardupdate lib/dns/zone.c:17897
    #3 forward_action lib/ns/update.c:3556
    #4 task_run lib/isc/task.c:857
    #5 isc_task_run lib/isc/task.c:950
    #6 isc__nm_async_task lib/isc/netmgr/netmgr.c:880
    #7 process_netievent lib/isc/netmgr/netmgr.c:959
    #8 process_queue lib/isc/netmgr/netmgr.c:1028
    #9 process_all_queues lib/isc/netmgr/netmgr.c:799
    #10 async_cb lib/isc/netmgr/netmgr.c:828
    #11 <null> <null>
    #12 isc__trampoline_run lib/isc/trampoline.c:191
    #13 <null> <null>

  Location is heap block of size 1310737 at 0x000000000016 allocated by main thread:
    #0 malloc <null>
    #1 default_memalloc lib/isc/mem.c:717
    #2 mem_get lib/isc/mem.c:626
    #3 mem_allocateunlocked lib/isc/mem.c:1292
    #4 isc___mem_allocate lib/isc/mem.c:1312
    #5 isc__mem_allocate lib/isc/mem.c:2563
    #6 isc___mem_get lib/isc/mem.c:1061
    #7 isc__mem_get lib/isc/mem.c:2542
    #8 isc__netmgr_create lib/isc/netmgr/netmgr.c:365
    #9 isc_managers_create lib/isc/managers.c:33
    #10 create_managers main.c:920
    #11 setup main.c:1245
    #12 main main.c:1548

  Thread T1 (running) created by main thread at:
    #0 pthread_create <null>
    #1 isc_thread_create lib/isc/pthreads/thread.c:79
    #2 isc__netmgr_create lib/isc/netmgr/netmgr.c:374
    #3 isc_managers_create lib/isc/managers.c:33
    #4 create_managers main.c:920
    #5 setup main.c:1245
    #6 main main.c:1548

  Thread T2 (running) created by main thread at:
    #0 pthread_create <null>
    #1 isc_thread_create lib/isc/pthreads/thread.c:79
    #2 isc__netmgr_create lib/isc/netmgr/netmgr.c:374
    #3 isc_managers_create lib/isc/managers.c:33
    #4 create_managers main.c:920
    #5 setup main.c:1245
    #6 main main.c:1548

SUMMARY: ThreadSanitizer: data race in __interceptor_recvmsg