data race in zonemgr_test

WARNING: ThreadSanitizer: data race 
  Write of size 8 at 0x000000000001 by main thread (mutexes: write M1):
    #0 free <null>
    #1 default_memfree lib/isc/mem.c:742
    #2 mem_put lib/isc/mem.c:654
    #3 isc___mem_put lib/isc/mem.c:1110
    #4 isc__mem_put lib/isc/mem.c:2439
    #5 ratelimiter_free lib/isc/ratelimiter.c:277
    #6 isc_ratelimiter_detach lib/isc/ratelimiter.c:300
    #7 zonemgr_free lib/dns/zone.c:17841
    #8 dns_zonemgr_detach lib/dns/zone.c:17653
    #9 zonemgr_createzone lib/dns/tests/zonemgr_test.c:145
    #10 <null> <null>
    #11 __libc_start_main ../csu/libc-start.c:308

  Previous write of size 8 at 0x000000000001 by thread T1 (mutexes: write M2):
    #0 dispatch lib/isc/task.c:1142
    #1 run lib/isc/task.c:1344
    #2 <null> <null>

  Mutex M1 (0x000000000014) created at:
    #0 pthread_mutex_init <null>
    #1 isc__mutex_init pthreads/mutex.c:288
    #2 mem_create lib/isc/mem.c:765
    #3 isc_mem_create lib/isc/mem.c:2425
    #4 dns_test_begin lib/dns/tests/dnstest.c:142
    #5 _setup lib/dns/tests/zonemgr_test.c:42
    #6 <null> <null>
    #7 __libc_start_main ../csu/libc-start.c:308

  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 lib/dns/tests/dnstest.c:116
    #4 dns_test_begin lib/dns/tests/dnstest.c:174
    #5 _setup lib/dns/tests/zonemgr_test.c:42
    #6 <null> <null>
    #7 __libc_start_main ../csu/libc-start.c:308

SUMMARY: ThreadSanitizer: data race in __interceptor_free