Debug audio output lock ordering

src/audio_output/aout_internal.h

@@ -164,51 +164,83 @@ int aout_DecGetResetLost( aout_instance_t *, aout_input_t * );
 void aout_DecChangePause( aout_instance_t *, aout_input_t *, bool b_paused, mtime_t i_date );
 void aout_DecFlush( aout_instance_t *, aout_input_t * );
 
-/* Helpers */
+/* Audio output locking */
+
+#if !defined (NDEBUG) \
+ && defined __linux__ && (defined (__i386__) || defined (__x86_64__))
+# define AOUT_DEBUG 1
+#endif
+
+#ifdef AOUT_DEBUG
+enum
+{
+    MIXER_LOCK=1,
+    INPUT_LOCK=2,
+    INPUT_FIFO_LOCK=4,
+    OUTPUT_FIFO_LOCK=8,
+};
+
+void aout_lock (unsigned);
+void aout_unlock (unsigned);
+
+#else
+# define aout_lock( i )   (void)0
+# define aout_unlock( i ) (void)0
+#endif
 
 static inline void aout_lock_mixer( aout_instance_t *p_aout )
 {
+    aout_lock( MIXER_LOCK );
     vlc_mutex_lock( &p_aout->mixer_lock );
 }
 
 static inline void aout_unlock_mixer( aout_instance_t *p_aout )
 {
+    aout_unlock( MIXER_LOCK );
     vlc_mutex_unlock( &p_aout->mixer_lock );
 }
 
 static inline void aout_lock_input_fifos( aout_instance_t *p_aout )
 {
+    aout_lock( INPUT_FIFO_LOCK );
     vlc_mutex_lock( &p_aout->input_fifos_lock );
 }
 
 static inline void aout_unlock_input_fifos( aout_instance_t *p_aout )
 {
+    aout_unlock( INPUT_FIFO_LOCK );
     vlc_mutex_unlock( &p_aout->input_fifos_lock );
 }
 
 static inline void aout_lock_output_fifo( aout_instance_t *p_aout )
 {
+    aout_lock( OUTPUT_FIFO_LOCK );
     vlc_mutex_lock( &p_aout->output_fifo_lock );
 }
 
 static inline void aout_unlock_output_fifo( aout_instance_t *p_aout )
 {
+    aout_unlock( OUTPUT_FIFO_LOCK );
     vlc_mutex_unlock( &p_aout->output_fifo_lock );
 }
 
 static inline void aout_lock_input( aout_instance_t *p_aout, aout_input_t * p_input )
 {
     (void)p_aout;
+    aout_lock( INPUT_LOCK );
     vlc_mutex_lock( &p_input->lock );
 }
 
 static inline void aout_unlock_input( aout_instance_t *p_aout, aout_input_t * p_input )
 {
     (void)p_aout;
+    aout_unlock( INPUT_LOCK );
     vlc_mutex_unlock( &p_input->lock );
 }
 
 
+/* Helpers */
+
 /**
  * This function will safely mark aout input to be restarted as soon as
  * possible to take configuration changes into account */

src/audio_output/common.c

@@ -114,6 +114,54 @@ static void aout_Destructor( vlc_object_t * p_this )
     vlc_mutex_destroy( &p_aout->output_fifo_lock );
 }
 
+/* Lock ordering rules:
+ *
+ *            Mixer Input IFIFO OFIFO (< Inner lock)
+ * Mixer       No!   N/A   Yes   Yes
+ * Input       N/A   No!   Yes   N/A
+ * In FIFOs    No!   No!   No!   No!
+ * Out FIFOs   No!   N/A   Yes   No!
+ * (^ Outer lock)
+ */
+#ifdef AOUT_DEBUG
+/* Lock debugging */
+static __thread unsigned aout_locks = 0;
+
+void aout_lock (unsigned i)
+{
+    unsigned allowed;
+    switch (i)
+    {
+        case MIXER_LOCK:
+            allowed = 0;
+            break;
+        case INPUT_LOCK:
+            allowed = 0;
+            break;
+        case OUTPUT_FIFO_LOCK:
+            allowed = MIXER_LOCK;
+            break;
+        case INPUT_FIFO_LOCK:
+            allowed = MIXER_LOCK|INPUT_LOCK|OUTPUT_FIFO_LOCK;
+            break;
+    }
+
+    if (aout_locks & ~allowed)
+    {
+        fprintf (stderr, "Illegal audio lock transition (%x -> %x)\n",
+                 aout_locks, aout_locks|i);
+        vlc_backtrace ();
+        //abort ();
+    }
+    aout_locks |= i;
+}
+
+void aout_unlock (unsigned i)
+{
+    assert (aout_locks & i);
+    aout_locks &= ~i;
+}
+#endif
 
 /*
  * Formats management (internal and external)