gmountsource: Fix deadlocks in synchronous API

Synchronous GMountSource API is implemented using the asynchronous API
with help of mutexes and conditions. But it seems that it is not guaranteed
that GAsyncReadyCallback is called on another thread and thus this solution
may cause deadlocks consequently. Let's rather use solution based on custom
mainloop to prevent potential deadlocks. Alternatively, we could use
synchronous API generated by gdbus-codegen to implement this functionality,
but the solution with custom mainloop seems to be less error-prone.

Closes: https://gitlab.gnome.org/GNOME/gvfs/issues/383

1 files changed, 29 insertions, 39 deletions

diff --git a/common/gmountsource.c b/common/gmountsource.c
index c5d9f1a3..d3307642 100644
--- a/common/gmountsource.c
+++ b/common/gmountsource.c
@@ -146,8 +146,8 @@ typedef struct AskSyncData AskSyncData;
 struct AskSyncData {
 
   /* For sync calls */
-  GMutex mutex;
-  GCond cond;
+  GMainContext *context;
+  GMainLoop *loop;
 
   /* results: */
   GAsyncResult *result;
@@ -375,10 +375,7 @@ ask_reply_sync  (GObject *source_object,
 
   data->result = g_object_ref (res);
 
-  /* Wake up sync call thread */
-  g_mutex_lock (&data->mutex);
-  g_cond_signal (&data->cond);
-  g_mutex_unlock (&data->mutex);
+  g_main_loop_quit (data->loop);
 }
 
 gboolean
@@ -397,11 +394,10 @@ g_mount_source_ask_password (GMountSource *source,
   gboolean handled;
   AskSyncData data;
 
-  memset (&data, 0, sizeof (data));
-  g_mutex_init (&data.mutex);
-  g_cond_init (&data.cond);
-  g_mutex_lock (&data.mutex);
+  data.context = g_main_context_new ();
+  data.loop = g_main_loop_new (data.context, FALSE);
 
+  g_main_context_push_thread_default (data.context);
 
   g_mount_source_ask_password_async (source,
                                      message_string,
@@ -411,13 +407,7 @@ g_mount_source_ask_password (GMountSource *source,
                                      ask_reply_sync,
                                      &data);
 
-  while (data.result == NULL)
-    g_cond_wait (&data.cond, &data.mutex);
-  g_mutex_unlock (&data.mutex);
-
-  g_cond_clear (&data.cond);
-  g_mutex_clear (&data.mutex);
-
+  g_main_loop_run (data.loop);
 
   handled = g_mount_source_ask_password_finish (source,
                                                 data.result,
@@ -427,6 +417,10 @@ g_mount_source_ask_password (GMountSource *source,
                                                 domain_out,
 						anonymous_out,
 						password_save_out);
+
+  g_main_context_pop_thread_default (data.context);
+  g_main_context_unref (data.context);
+  g_main_loop_unref (data.loop);
   g_object_unref (data.result);
 
   return handled;
@@ -562,11 +556,11 @@ g_mount_source_ask_question (GMountSource *source,
   gint choice;
   gboolean handled, aborted;
   AskSyncData data;
-  
-  memset (&data, 0, sizeof (data));
-  g_mutex_init (&data.mutex);
-  g_cond_init (&data.cond);
-  g_mutex_lock (&data.mutex);
+
+  data.context = g_main_context_new ();
+  data.loop = g_main_loop_new (data.context, FALSE);
+
+  g_main_context_push_thread_default (data.context);
 
   g_mount_source_ask_question_async (source,
                                      message,
@@ -574,18 +568,16 @@ g_mount_source_ask_question (GMountSource *source,
                                      ask_reply_sync,
                                      &data);
 
-  while (data.result == NULL)
-    g_cond_wait (&data.cond, &data.mutex);
-  g_mutex_unlock (&data.mutex);
-
-  g_cond_clear (&data.cond);
-  g_mutex_clear (&data.mutex);
+  g_main_loop_run (data.loop);
 
   handled = g_mount_source_ask_question_finish (source,
                                                 data.result,
                                                 &aborted,
                                                 &choice);
-  
+
+  g_main_context_pop_thread_default (data.context);
+  g_main_context_unref (data.context);
+  g_main_loop_unref (data.loop);
   g_object_unref (data.result);
 
   if (aborted_out)
@@ -833,10 +825,10 @@ g_mount_source_show_processes (GMountSource *source,
   gboolean handled, aborted;
   AskSyncData data;
 
-  memset (&data, 0, sizeof (data));
-  g_mutex_init (&data.mutex);
-  g_cond_init (&data.cond);
-  g_mutex_lock (&data.mutex);
+  data.context = g_main_context_new ();
+  data.loop = g_main_loop_new (data.context, FALSE);
+
+  g_main_context_push_thread_default (data.context);
 
   g_mount_source_show_processes_async (source,
                                        message,
@@ -845,18 +837,16 @@ g_mount_source_show_processes (GMountSource *source,
                                        ask_reply_sync,
                                        &data);
 
-  while (data.result == NULL)
-    g_cond_wait (&data.cond, &data.mutex);
-  g_mutex_unlock (&data.mutex);
-
-  g_cond_clear (&data.cond);
-  g_mutex_clear (&data.mutex);
+  g_main_loop_run (data.loop);
 
   handled = g_mount_source_show_processes_finish (source,
                                                   data.result,
                                                   &aborted,
                                                   &choice);
 
+  g_main_context_pop_thread_default (data.context);
+  g_main_context_unref (data.context);
+  g_main_loop_unref (data.loop);
   g_object_unref (data.result);
 
   if (aborted_out)