Made interactions to recording metadata threadsafe

Updating, freeing, and writing the recording metadata is now
threadsafe. This is in regards to the metadata that we receive from
the `rtpengine_offer` or `rtpengine_answer` commands, not the
`meta_fp` file.

We can simply use the `call->master_lock` variable for protecting
updates to the recording metadata. We had to move the metadata
handling code in call_interfaces.c up into the master_lock guarded
section. The code in "recording.c:meta_finish_file" is called with
master_lock protection already.

daemon/call_interfaces.c

@@ -720,26 +720,6 @@ static const char *call_offer_answer_ng(bencode_item_t *input, struct callmaster
 	if (!ret)
 		ret = sdp_replace(chopper, &parsed, monologue->active_dialogue, &flags);
 
-	rwlock_unlock_w(&call->master_lock);
-	redis_update(call, m->conf.redis_write);
-	obj_put(call);
-
-	gettimeofday(&(monologue->started), NULL);
-
-	errstr = "Error rewriting SDP";
-
-	if (ret == ERROR_NO_FREE_PORTS || ret == ERROR_NO_FREE_LOGS) {
-		ilog(LOG_ERR, "Destroying call");
-		call_destroy(call);
-	}
-
-	if (ret)
-		goto out;
-
-	bencode_dictionary_add_iovec(output, "sdp", &g_array_index(chopper->iov, struct iovec, 0),
-		chopper->iov_num, chopper->str_len);
-	bencode_dictionary_add_string(output, "result", "ok");
-
 	struct recording *recording = call->recording;
 	if (call->record_call && recording != NULL && recording->meta_fp != NULL) {
 		struct iovec *iov = &g_array_index(chopper->iov, struct iovec, 0);
@@ -751,6 +731,7 @@ static const char *call_offer_answer_ng(bencode_item_t *input, struct callmaster
 	if (metadata.len > 0 && call->recording != NULL) {
 		if (call->recording->metadata != NULL) {
 			free(call->recording->metadata);
+			call->recording->metadata = NULL;
 		}
 		call->recording->metadata = str_dup(&metadata);
 	}
@@ -760,6 +741,26 @@ static const char *call_offer_answer_ng(bencode_item_t *input, struct callmaster
 		bencode_list_add_string(recordings, recording_path);
 	}
 
+	rwlock_unlock_w(&call->master_lock);
+	redis_update(call, m->conf.redis_write);
+	obj_put(call);
+
+	gettimeofday(&(monologue->started), NULL);
+
+	errstr = "Error rewriting SDP";
+
+	if (ret == ERROR_NO_FREE_PORTS || ret == ERROR_NO_FREE_LOGS) {
+		ilog(LOG_ERR, "Destroying call");
+		call_destroy(call);
+	}
+
+	if (ret)
+		goto out;
+
+	bencode_dictionary_add_iovec(output, "sdp", &g_array_index(chopper->iov, struct iovec, 0),
+		chopper->iov_num, chopper->str_len);
+	bencode_dictionary_add_string(output, "result", "ok");
+
 	errstr = NULL;
 out:
 	sdp_free(&parsed);

daemon/recording.c

@@ -231,6 +231,7 @@ ssize_t meta_write_sdp(FILE *meta_fp, struct iovec *sdp_iov, int iovcnt,
  * Returns non-zero for failure.
  */
 int meta_finish_file(struct call *call) {
+	// This should usually be called from a place that has the call->master_lock
 	struct recording *recording = call->recording;
 	int return_code = 0;
 
@@ -251,6 +252,7 @@ int meta_finish_file(struct call *call) {
 		// Print metadata
 		fprintf(recording->meta_fp, "\n\n%s\n", recording->metadata->s);
 		free(recording->metadata);
+		recording->metadata = NULL;
 		fclose(recording->meta_fp);
 
 		// Get the filename (in between its directory and the file extension)