Make taking a global lock automatically initialize locking if needed

This lets them be thread-safe by default, at the cost that they can
now fail.

init_uninitialized_locks() and init_global_locks() must now both
reimplement the equivalent of _dbus_register_shutdown_func(), by using
_dbus_platform_rmutex_lock() on the same underlying mutex around a call
to _dbus_register_shutdown_func_unlocked().

This is because if they used the usual _DBUS_LOCK() API (as
_dbus_register_shutdown_func() does), it would automatically try to
initialize global locking, leading to infinite recursion.

Bug: https://bugs.freedesktop.org/show_bug.cgi?id=54972
Signed-off-by: Simon McVittie <simon.mcvittie@collabora.co.uk>
Reviewed-by: Alban Crequy <alban.crequy@collabora.co.uk>
Reviewed-by: Anas Nashif <anas.nashif@intel.com>

1 files changed, 16 insertions, 3 deletions

diff --git a/dbus/dbus-message.c b/dbus/dbus-message.c
index bc2380f8..696991f6 100644
--- a/dbus/dbus-message.c
+++ b/dbus/dbus-message.c
@@ -516,7 +516,9 @@ dbus_message_cache_shutdown (void *data)
 {
   int i;
 
-  _DBUS_LOCK (message_cache);
+  if (!_DBUS_LOCK (message_cache))
+    _dbus_assert_not_reached ("we would have initialized global locks "
+        "before registering a shutdown function");
 
   i = 0;
   while (i < MAX_MESSAGE_CACHE_SIZE)
@@ -548,7 +550,12 @@ dbus_message_get_cached (void)
 
   message = NULL;
 
-  _DBUS_LOCK (message_cache);
+  if (!_DBUS_LOCK (message_cache))
+    {
+      /* we'd have initialized global locks before caching anything,
+       * so there can't be anything in the cache */
+      return NULL;
+    }
 
   _dbus_assert (message_cache_count >= 0);
 
@@ -660,7 +667,13 @@ dbus_message_cache_or_finalize (DBusMessage *message)
 
   was_cached = FALSE;
 
-  _DBUS_LOCK (message_cache);
+  if (!_DBUS_LOCK (message_cache))
+    {
+      /* The only way to get a non-null message goes through
+       * dbus_message_get_cached() which takes the lock. */
+      _dbus_assert_not_reached ("we would have initialized global locks "
+          "the first time we constructed a message");
+    }
 
   if (!message_cache_shutdown_registered)
     {