Work-around for deadlock in DbcCtl instance initialization when loading plugins.

include/tscore/DbgCtl.h

@@ -59,4 +59,27 @@ class DbgCtl
   friend TSDbgCtl const *TSDbgCtlCreate(char const *tag);
 
   friend void TSDbgCtlDestroy(TSDbgCtl const *dbg_ctl);
+
+public:
+  // When loading an ATS plugin with dlopen(), an instance of this class should exist in the stack.  This will prevent
+  // https://github.com/apache/trafficserver/issues/10129 .  It will prevent DbgCtl member functions from indiredtly
+  // calling Regex::compile(), which calls a function that defines a thread_local variable.  Such functions try to lock
+  // the same global mutex (in the C/C++ runtime) that is locked when dlopen() is in progress.  This prevents a deadlock
+  // where shared library static initialization is holding the global mutex and waiting on the Registry mutex, and
+  // a DbgCtl intanstantiantion has called Regex::compile() in a different thread, is holding the Registry mutex, and
+  // waiting on the global mutex.
+  //
+  class Guard_dlopen
+  {
+  public:
+    Guard_dlopen();
+    ~Guard_dlopen();
+
+    // No copying.
+    Guard_dlopen(Guard_dlopen const &)            = delete;
+    Guard_dlopen &operator=(Guard_dlopen const &) = delete;
+
+  private:
+    _RegistryAccessor *rap;
+  };
 };

proxy/Plugin.cc

@@ -31,6 +31,7 @@
 #include "Plugin.h"
 #include "tscore/ink_cap.h"
 #include "tscore/Filenames.h"
+#include "tscore/DbgCtl.h"
 
 #define MAX_PLUGIN_ARGS 64
 
@@ -102,8 +103,11 @@ PluginRegInfo::~PluginRegInfo()
 bool
 plugin_dso_load(const char *path, void *&handle, void *&init, std::string &error)
 {
-  handle = dlopen(path, RTLD_NOW);
-  init   = nullptr;
+  {
+    DbgCtl::Guard_dlopen g;
+    handle = dlopen(path, RTLD_NOW);
+  }
+  init = nullptr;
   if (!handle) {
     error.assign("unable to load '").append(path).append("': ").append(dlerror());
     Error("%s", error.c_str());

proxy/http/remap/PluginDso.cc

@@ -34,6 +34,7 @@
 #include "unit-tests/plugin_testing_common.h"
 #else
 #include "tscore/Diags.h"
+#include "tscore/DbgCtl.h"
 #define PluginDebug Debug
 #define PluginError Error
 #endif
@@ -105,10 +106,15 @@ PluginDso::load(std::string &error)
 
       /* Now attempt to load the plugin DSO */
 #if defined(darwin)
-      if (!dlopen_preflight(_runtimePath.c_str()) || (_dlh = dlopen(_runtimePath.c_str(), RTLD_NOW | RTLD_LOCAL)) == nullptr) {
-#else
-      if ((_dlh = dlopen(_runtimePath.c_str(), RTLD_NOW | RTLD_LOCAL)) == nullptr) {
+      if (!dlopen_preflight(_runtimePath.c_str())) {
+        _dlh = nullptr;
+      } else
 #endif
+      {
+        DbgCtl::Guard_dlopen g;
+        _dlh = dlopen(_runtimePath.c_str(), RTLD_NOW | RTLD_LOCAL);
+      }
+      if (_dlh == nullptr) {
         const char *err = dlerror();
         concat_error(error, err ? err : "unknown dlopen() error");
         _dlh = nullptr; /* mark that the constructor failed. */

src/tscore/DbgCtl.cc

@@ -66,7 +66,7 @@ class DbgCtl::_RegistryAccessor
       _mtx.unlock();
     }
 
-    std::mutex _mtx;
+    std::recursive_mutex _mtx;
 
     friend class DbgCtl::_RegistryAccessor;
   };
@@ -195,3 +195,10 @@ DbgCtl::update()
     const_cast<char volatile &>(i.on) = diags()->tag_activated(i.tag, DiagsTagType_Debug);
   }
 }
+
+DbgCtl::Guard_dlopen::Guard_dlopen() : rap{new _RegistryAccessor} {};
+
+DbgCtl::Guard_dlopen::~Guard_dlopen()
+{
+  delete rap;
+}