diff --git a/.github/workflows/selfdrive_tests.yaml b/.github/workflows/selfdrive_tests.yaml
index f04eaad86..46ab32c36 100644
--- a/.github/workflows/selfdrive_tests.yaml
+++ b/.github/workflows/selfdrive_tests.yaml
@@ -260,6 +260,7 @@ jobs:
                         $UNIT_TEST tools/lib/tests && \
                         ./selfdrive/boardd/tests/test_boardd_usbprotocol && \
                         ./selfdrive/common/tests/test_util && \
+                        ./selfdrive/common/tests/test_swaglog && \
                         ./selfdrive/loggerd/tests/test_logger &&\
                         ./selfdrive/proclogd/tests/test_proclog && \
                         ./selfdrive/ui/replay/tests/test_replay && \
diff --git a/selfdrive/common/SConscript b/selfdrive/common/SConscript
index 9b496fef7..21f609865 100644
--- a/selfdrive/common/SConscript
+++ b/selfdrive/common/SConscript
@@ -33,3 +33,4 @@ Export('_common', '_gpucommon', '_gpu_libs')
 
 if GetOption('test'):
   env.Program('tests/test_util', ['tests/test_util.cc'], LIBS=[_common])
+  env.Program('tests/test_swaglog', ['tests/test_swaglog.cc'], LIBS=[_common, 'json11', 'zmq', 'pthread'])
diff --git a/selfdrive/common/swaglog.cc b/selfdrive/common/swaglog.cc
index 74488e220..d8c7d036d 100644
--- a/selfdrive/common/swaglog.cc
+++ b/selfdrive/common/swaglog.cc
@@ -82,9 +82,7 @@ static void cloudlog_init() {
   s.inited = true;
 }
 
-void log(int levelnum, const char* filename, int lineno, const char* func, const char* msg, const std::string& log_s) {
-  std::lock_guard lk(s.lock);
-  cloudlog_init();
+static void log(int levelnum, const char* filename, int lineno, const char* func, const char* msg, const std::string& log_s) {
   if (levelnum >= s.print_level) {
     printf("%s: %s\n", filename, msg);
   }
@@ -97,10 +95,13 @@ void cloudlog_e(int levelnum, const char* filename, int lineno, const char* func
   char* msg_buf = nullptr;
   va_list args;
   va_start(args, fmt);
-  vasprintf(&msg_buf, fmt, args);
+  int ret = vasprintf(&msg_buf, fmt, args);
   va_end(args);
 
-  if (!msg_buf) return;
+  if (ret <= 0 || !msg_buf) return;
+
+  std::lock_guard lk(s.lock);
+  cloudlog_init();
 
   json11::Json log_j = json11::Json::object {
     {"msg", msg_buf},
diff --git a/selfdrive/common/tests/.gitignore b/selfdrive/common/tests/.gitignore
index 2b7a3c6eb..1350b3b82 100644
--- a/selfdrive/common/tests/.gitignore
+++ b/selfdrive/common/tests/.gitignore
@@ -1 +1,2 @@
 test_util
+test_swaglog
diff --git a/selfdrive/common/tests/test_swaglog.cc b/selfdrive/common/tests/test_swaglog.cc
new file mode 100644
index 000000000..e4d333fd4
--- /dev/null
+++ b/selfdrive/common/tests/test_swaglog.cc
@@ -0,0 +1,86 @@
+#include <zmq.h>
+#include <iostream>
+#define CATCH_CONFIG_MAIN
+#include "catch2/catch.hpp"
+
+#include "json11.hpp"
+#include "selfdrive/common/swaglog.h"
+#include "selfdrive/common/util.h"
+#include "selfdrive/common/version.h"
+#include "selfdrive/hardware/hw.h"
+
+const char *SWAGLOG_ADDR = "ipc:///tmp/logmessage";
+std::string dongle_id = "test_dongle_id";
+
+void log_thread(int msg, int msg_cnt) {
+  for (int i = 0; i < msg_cnt; ++i) {
+    LOGD("%d", msg);
+    usleep(1);
+  }
+}
+
+void send_stop_msg(void *zctx) {
+  void *sock = zmq_socket(zctx, ZMQ_PUSH);
+  zmq_connect(sock, SWAGLOG_ADDR);
+  zmq_send(sock, "", 0, ZMQ_NOBLOCK);
+  zmq_close(sock);
+}
+
+void recv_log(void *zctx, int thread_cnt, int thread_msg_cnt) {
+  void *sock = zmq_socket(zctx, ZMQ_PULL);
+  zmq_bind(sock, SWAGLOG_ADDR);
+  std::vector<int> thread_msgs(thread_cnt);
+
+  while (true) {
+    char buf[4096] = {};
+    if (zmq_recv(sock, buf, sizeof(buf), 0) == 0) break;
+
+    REQUIRE(buf[0] == CLOUDLOG_DEBUG);
+    std::string err;
+    auto msg = json11::Json::parse(buf + 1, err);
+    REQUIRE(!msg.is_null());
+
+    REQUIRE(msg["levelnum"].int_value() == CLOUDLOG_DEBUG);
+    REQUIRE_THAT(msg["filename"].string_value(), Catch::Contains("test_swaglog.cc"));
+    REQUIRE(msg["funcname"].string_value() == "log_thread");
+    REQUIRE(msg["lineno"].int_value() == 17);
+
+    auto ctx = msg["ctx"];
+    REQUIRE(ctx["dongle_id"].string_value() == dongle_id);
+    REQUIRE(ctx["version"].string_value() == COMMA_VERSION);
+    REQUIRE(ctx["dirty"].bool_value() == true);
+    std::string device = "pc";
+    if (Hardware::EON()) {
+      device = "eon";
+    } else if (Hardware::TICI()) {
+      device = "tici";
+    }
+    REQUIRE(ctx["device"].string_value() == device);
+
+    int thread_id = atoi(msg["msg"].string_value().c_str());
+    REQUIRE((thread_id >= 0 && thread_id < thread_cnt));
+    thread_msgs[thread_id]++;
+  }
+  for (int i = 0; i < thread_cnt; ++i) {
+    REQUIRE(thread_msgs[i] == thread_msg_cnt);
+  }
+  zmq_close(sock);
+}
+
+TEST_CASE("swaglog") {
+  setenv("DONGLE_ID", dongle_id.c_str(), 1);
+  setenv("dirty", "1", 1);
+  const int thread_cnt = 5;
+  const int thread_msg_cnt = 100;
+
+  void *zctx = zmq_ctx_new();
+  send_stop_msg(zctx);
+  std::vector<std::thread> log_threads;
+  for (int i = 0; i < thread_cnt; ++i) {
+    log_threads.push_back(std::thread(log_thread, i, thread_msg_cnt));
+  }
+
+  for (auto &t : log_threads) t.join();
+  recv_log(zctx, thread_cnt, thread_msg_cnt);
+  zmq_ctx_destroy(zctx);
+}