vout: protect filter chain creation/destruction

Windows can send input events even if there is no display, so the
filter chains may need to be accessed even then. This protects the
creation and destruction of the chains with the existing filter lock,
providing memory safety.

src/video_output/video_output.c

@@ -2101,6 +2101,8 @@ static void ProcessMouseState(vout_thread_sys_t *p_vout,
 static int vout_Start(vout_thread_sys_t *vout, vlc_video_context *vctx, const vout_configuration_t *cfg)
 {
     vout_thread_sys_t *sys = vout;
+    filter_chain_t *cs, *ci;
+
     assert(!sys->dummy);
 
     sys->mouse_event = cfg->mouse_event;
@@ -2125,10 +2127,16 @@ static int vout_Start(vout_thread_sys_t *vout, vlc_video_context *vctx, const vo
         .video = &static_cbs,
         .sys = vout,
     };
-    sys->filter.chain_static = filter_chain_NewVideo(&vout->obj, true, &owner);
+
+    cs = filter_chain_NewVideo(&vout->obj, true, &owner);
 
     owner.video = &interactive_cbs;
-    sys->filter.chain_interactive = filter_chain_NewVideo(&vout->obj, true, &owner);
+    ci = filter_chain_NewVideo(&vout->obj, true, &owner);
+
+    vlc_mutex_lock(&sys->filter.lock);
+    sys->filter.chain_static = cs;
+    sys->filter.chain_interactive = ci;
+    vlc_mutex_unlock(&sys->filter.lock);
 
     vout_display_cfg_t dcfg;
     struct vout_crop crop;
@@ -2200,12 +2208,17 @@ static int vout_Start(vout_thread_sys_t *vout, vlc_video_context *vctx, const vo
     return VLC_SUCCESS;
 error:
     if (sys->filter.chain_interactive != NULL)
-    {
         DelAllFilterCallbacks(vout);
-        filter_chain_Delete(sys->filter.chain_interactive);
-    }
-    if (sys->filter.chain_static != NULL)
-        filter_chain_Delete(sys->filter.chain_static);
+    vlc_mutex_lock(&sys->filter.lock);
+    ci = sys->filter.chain_interactive;
+    cs = sys->filter.chain_static;
+    sys->filter.chain_interactive = NULL;
+    sys->filter.chain_static = NULL;
+    vlc_mutex_unlock(&sys->filter.lock);
+    if (ci != NULL)
+        filter_chain_Delete(ci);
+    if (cs != NULL)
+        filter_chain_Delete(cs);
     video_format_Clean(&sys->filter.src_fmt);
     if (sys->filter.src_vctx)
     {
@@ -2338,6 +2351,7 @@ static void *Thread(void *object)
 static void vout_ReleaseDisplay(vout_thread_sys_t *vout)
 {
     vout_thread_sys_t *sys = vout;
+    filter_chain_t *ci, *cs;
 
     assert(sys->display != NULL);
 
@@ -2355,8 +2369,14 @@ static void vout_ReleaseDisplay(vout_thread_sys_t *vout)
 
     /* Destroy the video filters */
     DelAllFilterCallbacks(vout);
-    filter_chain_Delete(sys->filter.chain_interactive);
-    filter_chain_Delete(sys->filter.chain_static);
+    vlc_mutex_lock(&sys->filter.lock);
+    ci = sys->filter.chain_interactive;
+    cs = sys->filter.chain_static;
+    sys->filter.chain_interactive = NULL;
+    sys->filter.chain_static = NULL;
+    vlc_mutex_unlock(&sys->filter.lock);
+    filter_chain_Delete(ci);
+    filter_chain_Delete(cs);
     video_format_Clean(&sys->filter.src_fmt);
     if (sys->filter.src_vctx)
     {