From a241c69920fe5a609305fb435b593c2d997626aa Mon Sep 17 00:00:00 2001
From: Mark Andrews <marka@isc.org>
Date: Thu, 15 Oct 2020 15:05:30 +1100
Subject: [PATCH] Lock read of refs when atomics are not available.

    WARNING: ThreadSanitizer: data race
    Read of size 4 at 0x000000000001 by thread T1 (mutexes: write M1):
    #0 zone_iattach lib/dns/zone.c:5412:2
    #1 soa_query lib/dns/zone.c:12725:2
    #2 dispatch lib/isc/task.c:1157:7
    #3 run lib/isc/task.c:1331:2

    Previous write of size 4 at 0x000000000001 by thread T2 (mutexes: write M2):
    #0 dns_zone_detach lib/dns/zone.c:5346:2
    #1 ns_server_refreshcommand bin/named/./server.c:9880:3
    #2 ns_control_docommand bin/named/control.c:247:12
    #3 control_recvmessage bin/named/controlconf.c:469:13
    #4 dispatch lib/isc/task.c:1157:7
    #5 run lib/isc/task.c:1331:2
Conflict: NA
Reference: https://gitlab.isc.org/isc-projects/bind9/-/commit/a241c69920fe5a609305fb435b593c2d997626aa
---
 lib/isc/include/isc/refcount.h |  2 +-
 lib/isc/refcount.c             | 15 +++++++++++++++
 2 files changed, 16 insertions(+), 1 deletion(-)

diff --git a/lib/isc/include/isc/refcount.h b/lib/isc/include/isc/refcount.h
index 5d1a5d2bbf..1c9696fc6b 100644
--- a/lib/isc/include/isc/refcount.h
+++ b/lib/isc/include/isc/refcount.h
@@ -211,7 +211,7 @@ typedef struct isc_refcount {
 		ISC_ERROR_RUNTIMECHECK(_result == ISC_R_SUCCESS);	\
 	} while (0)
 
-#define isc_refcount_current(rp) ((unsigned int)((rp)->refs))
+unsigned int isc_refcount_current(isc_refcount_t *rp);
 
 /*%
  * Increments the reference count, returning the new value in
diff --git a/lib/isc/refcount.c b/lib/isc/refcount.c
index d83c82fe7f..0d961effe1 100644
--- a/lib/isc/refcount.c
+++ b/lib/isc/refcount.c
@@ -19,6 +19,21 @@
 #include <isc/result.h>
 #include <isc/util.h>
 
+#if defined(ISC_PLATFORM_USETHREADS) && !defined(ISC_REFCOUNT_HAVEATOMIC)
+unsigned int
+isc_refcount_current(isc_refcount_t *ref) {
+	isc_result_t result;
+	unsigned int answer;
+
+	result = isc_mutex_lock(&ref->lock);
+	ISC_ERROR_RUNTIMECHECK(result == ISC_R_SUCCESS);
+	answer = ref->refs;
+	result = isc_mutex_unlock(&ref->lock);
+	ISC_ERROR_RUNTIMECHECK(result == ISC_R_SUCCESS);
+	return (answer);
+}
+#endif
+
 isc_result_t
 isc_refcount_init(isc_refcount_t *ref, unsigned int n) {
 	REQUIRE(ref != NULL);
-- 
2.23.0

