ThreadSanitizer: data race lib/isc/netmgr/tcpdns.c:1091:12 in isc__nm_tcpdns_send

Job #2502181 failed for 4df5a54e9b61aa6fd8b9dad3adaa1d39340ae62b on the v9_16_sub branch, which is basically 9.16.28-S1.

WARNING: ThreadSanitizer: data race 
  Read of size 8 at 0x000000000001 by thread T1:
    #0 isc__nm_tcpdns_send lib/isc/netmgr/tcpdns.c:1091:12
    #1 isc_nm_send lib/isc/netmgr/netmgr.c:2438:3
    #2 client_sendpkg lib/ns/client.c:355:2
    #3 ns_client_send lib/ns/client.c:697:3
    #4 query_send lib/ns/query.c:584:2
    #5 ns_query_done lib/ns/query.c:11959:2
    #6 query_respond lib/ns/query.c:8435:10
    #7 query_prepresponse lib/ns/query.c:10969:10
    #8 query_gotanswer lib/ns/query.c
    #9 query_resume lib/ns/query.c:6886:10
    #10 fetch_callback lib/ns/query.c:6442:12
    #11 task_run lib/isc/task.c:851:5
    #12 isc_task_run lib/isc/task.c:944:10
    #13 process_netievent lib/isc/netmgr/netmgr.c
    #14 process_queue lib/isc/netmgr/netmgr.c:1040:16
    #15 process_all_queues lib/isc/netmgr/netmgr.c:814:25
    #16 async_cb lib/isc/netmgr/netmgr.c:842:6
    #17 uv__async_io /usr/src/libuv-v1.43.0/src/unix/async.c:163:5
    #18 isc__trampoline_run lib/isc/trampoline.c:209:11

  Previous write of size 8 at 0x000000000001 by thread T2:
    #0 isc__nm_tcpdns_send lib/isc/netmgr/tcpdns.c:1092:23
    #1 isc_nm_send lib/isc/netmgr/netmgr.c:2438:3
    #2 client_sendpkg lib/ns/client.c:355:2
    #3 ns_client_send lib/ns/client.c:697:3
    #4 query_send lib/ns/query.c:584:2
    #5 ns_query_done lib/ns/query.c:11959:2
    #6 query_respond lib/ns/query.c:8435:10
    #7 query_prepresponse lib/ns/query.c:10969:10
    #8 query_gotanswer lib/ns/query.c
    #9 query_resume lib/ns/query.c:6886:10
    #10 fetch_callback lib/ns/query.c:6442:12
    #11 task_run lib/isc/task.c:851:5
    #12 isc_task_run lib/isc/task.c:944:10
    #13 process_netievent lib/isc/netmgr/netmgr.c
    #14 process_queue lib/isc/netmgr/netmgr.c:1040:16
    #15 process_all_queues lib/isc/netmgr/netmgr.c:814:25
    #16 async_cb lib/isc/netmgr/netmgr.c:842:6
    #17 uv__async_io /usr/src/libuv-v1.43.0/src/unix/async.c:163:5
    #18 isc__trampoline_run lib/isc/trampoline.c:209:11

  Location is heap block of size 1361 at 0x000000000018 allocated by thread T3:
    #0 malloc <null>
    #1 default_memalloc lib/isc/mem.c:715:8
    #2 mem_get lib/isc/mem.c:624:8
    #3 mem_allocateunlocked lib/isc/mem.c:1289:8
    #4 isc___mem_allocate lib/isc/mem.c:1309:7
    #5 isc__mem_allocate lib/isc/mem.c:2399:10
    #6 isc___mem_get lib/isc/mem.c:1059:11
    #7 isc__mem_get lib/isc/mem.c:2378:10
    #8 accept_connection lib/isc/netmgr/tcpdns.c:956:10
    #9 tcpdns_connection_cb lib/isc/netmgr/tcpdns.c:624:11
    #10 uv__server_io /usr/src/libuv-v1.43.0/src/unix/stream.c:570:5
    #11 isc__trampoline_run lib/isc/trampoline.c:209:11

  Thread T1 (running) created by main thread at:
    #0 pthread_create <null>
    #1 isc_thread_create lib/isc/pthreads/thread.c:81:8
    #2 isc__netmgr_create lib/isc/netmgr/netmgr.c:370:3
    #3 isc_managers_create lib/isc/managers.c:35:2
    #4 create_managers bin/named/./main.c:931:11
    #5 setup bin/named/./main.c:1256:11
    #6 main bin/named/./main.c:1576:2

  Thread T2 (running) created by main thread at:
    #0 pthread_create <null>
    #1 isc_thread_create lib/isc/pthreads/thread.c:81:8
    #2 isc__netmgr_create lib/isc/netmgr/netmgr.c:370:3
    #3 isc_managers_create lib/isc/managers.c:35:2
    #4 create_managers bin/named/./main.c:931:11
    #5 setup bin/named/./main.c:1256:11
    #6 main bin/named/./main.c:1576:2

  Thread T3 (running) created by main thread at:
    #0 pthread_create <null>
    #1 isc_thread_create lib/isc/pthreads/thread.c:81:8
    #2 isc__netmgr_create lib/isc/netmgr/netmgr.c:370:3
    #3 isc_managers_create lib/isc/managers.c:35:2
    #4 create_managers bin/named/./main.c:931:11
    #5 setup bin/named/./main.c:1256:11
    #6 main bin/named/./main.c:1576:2

SUMMARY: ThreadSanitizer: data race lib/isc/netmgr/tcpdns.c:1091:12 in isc__nm_tcpdns_send