Index: main/pbx.c
===================================================================
--- main/pbx.c	(revision 386603)
+++ main/pbx.c	(working copy)
@@ -1212,7 +1212,7 @@
  * This lock MUST be recursive, or a deadlock on reload may result.  See
  * https://issues.asterisk.org/view.php?id=17643
  */
-AST_MUTEX_DEFINE_STATIC(conlock);
+AST_RWLOCK_DEFINE_STATIC(conlock);
 
 /*!
  * \brief Lock to hold off restructuring of hints by ast_merge_contexts_and_delete.
@@ -10614,19 +10614,75 @@
 /*
  * Lock context list functions ...
  */
+AST_THREADSTORAGE(conlock_read_count);
+struct conlock_count {
+	unsigned int count;
+	unsigned int isreadwrite:2;
+};
+#define CONLOCK_READ 1
+#define CONLOCK_WRITE 2
+
 int ast_wrlock_contexts(void)
 {
-	return ast_mutex_lock(&conlock);
+	struct conlock_count *buf = ast_threadstorage_get(&conlock_read_count, sizeof(*buf));
+	int res = 0;
+	/* An original wrlock may be escalated by either rdlock or wrlock, but an
+	 * original rdlock is escalatable only by another rdlock. */
+	if (buf->isreadwrite == CONLOCK_READ) {
+		return EDEADLK;
+	}
+
+	if (buf->count > 0) {
+		buf->count++;
+	} else if ((res = ast_rwlock_wrlock(&conlock)) == 0) {
+		buf->count = 1;
+		buf->isreadwrite = CONLOCK_WRITE;
+	} else {
+		ast_log(LOG_ERROR, "Unhandled lock error condition?!! (%d) %s\n", res, strerror(res));
+	}
+	return res;
 }
 
 int ast_rdlock_contexts(void)
 {
-	return ast_mutex_lock(&conlock);
+	struct conlock_count *buf = ast_threadstorage_get(&conlock_read_count, sizeof(*buf));
+	int res = 0;
+
+	if (buf->count > 0) {
+		/* Already locked -- make it recursively locked one more time. */
+		buf->count++;
+	} else if ((res = ast_rwlock_rdlock(&conlock)) == 0) {
+		buf->isreadwrite = CONLOCK_READ;
+		buf->count = 1;
+	} else {
+		ast_log(LOG_ERROR, "Unhandled lock error condition?!! (%d) %s\n", res, strerror(res));
+	}
+	return res;
 }
 
 int ast_unlock_contexts(void)
 {
-	return ast_mutex_unlock(&conlock);
+	struct conlock_count *buf = ast_threadstorage_get(&conlock_read_count, sizeof(*buf));
+	int res = 0;
+	if (buf->count > 1) {
+		buf->count--;
+	} else if (buf->count == 0) {
+		/* No lock held */
+		return EPERM;
+	} else if ((res = ast_rwlock_unlock(&conlock)) == 0) {
+		buf->count = 0;
+		/* Reset flags, so next time in the same thread, we can change the type of lock. */
+		buf->isreadwrite = 0;
+	} else if (res == EPERM) {
+		/* This should never occur -- it would mean that we unlock conlock outside of this function. */
+		ast_log(LOG_ERROR, "Programming bug -- unlocked elsewhere?!!\n");
+		buf->count = 0;
+		buf->isreadwrite = 0;
+	} else {
+		ast_log(LOG_ERROR, "Unhandled lock error: (%d) %s\n", res, strerror(res));
+	}
+
+	return res;
 }
 
 /*