ThreadSanitizer: data race dispatch.c:901 in free_buffer

Binary: named Commit: c5b6f215 Tests: kasp, masterformat

WARNING: ThreadSanitizer: data race (pid=95127)
  Write of size 4 at 0x7b540000ffd8 by thread T6 (mutexes: write M533530767473606080, write M457813912839061400):
    #0 free_buffer dispatch.c:901 (libdns.1503.dylib:x86_64+0x3962c)
    #1 udp_recv dispatch.c:1106 (libdns.1503.dylib:x86_64+0x3d568)
    #2 udp_exrecv dispatch.c:997 (libdns.1503.dylib:x86_64+0x3c26c)
    #3 run task.c:1134 (libisc.1503.dylib:x86_64+0x2c9e1)

  Previous read of size 4 at 0x7b540000ffd8 by thread T5 (mutexes: write M572937264213096384):
    #0 udp_recv dispatch.c:1050 (libdns.1503.dylib:x86_64+0x3ce2e)
    #1 udp_exrecv dispatch.c:997 (libdns.1503.dylib:x86_64+0x3c26c)
    #2 run task.c:1134 (libisc.1503.dylib:x86_64+0x2c9e1)

  Location is heap block of size 625 at 0x7b540000ff00 allocated by thread T5:
    #0 malloc <null>:6891872 (libclang_rt.tsan_osx_dynamic.dylib:x86_64h+0x4e65a)
    #1 default_memalloc mem.c:685 (libisc.1503.dylib:x86_64+0x17ae1)
    #2 run_server server.c:9588 (named:x86_64+0x10000db5a)
    #3 run task.c:1134 (libisc.1503.dylib:x86_64+0x2c9e1)

  Mutex M533530767473606080 is already destroyed.

  Mutex M457813912839061400 is already destroyed.

  Mutex M572937264213096384 is already destroyed.

  Thread T6 (tid=4862704, running) created by main thread at:
    #0 pthread_create <null>:6891920 (libclang_rt.tsan_osx_dynamic.dylib:x86_64h+0x2a9cd)
    #1 isc_thread_create thread.c:75 (libisc.1503.dylib:x86_64+0x46d1c)
    #2 main main.c:902 (named:x86_64+0x10000ad16)

  Thread T5 (tid=4862703, running) created by main thread at:
    #0 pthread_create <null>:6891920 (libclang_rt.tsan_osx_dynamic.dylib:x86_64h+0x2a9cd)
    #1 isc_thread_create thread.c:75 (libisc.1503.dylib:x86_64+0x46d1c)
    #2 main main.c:902 (named:x86_64+0x10000ad16)

SUMMARY: ThreadSanitizer: data race dispatch.c:901 in free_buffer