st/dri: Track drawable context bindings

Needs to track this ourself since because we get into a race condition with
the dri_util.c code on make current when rendering to the front buffer.

This is what happens:
Old context is rendering to the front buffer.

App calls MakeCurrent with a new context. dri_util.c sets
drawable->driContextPriv to the new context and then calls the driver make
current. st/dri make current flushes the old context, which calls back into
st/dri via the flush frontbuffer hook. st/dri calls dri loader flush
frontbuffer, which calls invalidate buffer on the drawable into st/dri.

This is where things gets wrong. st/dri grabs the context from the dri
drawable (which now points to the new context) and calls invalidate
framebuffer to the new context which has not yet set the new drawable as its
framebuffers since we have not called make current yet, it asserts.

src/gallium/state_trackers/dri/common/dri_context.c

@@ -141,12 +141,18 @@ GLboolean
 dri_unbind_context(__DRIcontext * cPriv)
 {
    /* dri_util.c ensures cPriv is not null */
+   struct dri_screen *screen = dri_screen(cPriv->driScreenPriv);
    struct dri_context *ctx = dri_context(cPriv);
+   struct dri_drawable *draw = dri_drawable(ctx->dPriv);
+   struct dri_drawable *read = dri_drawable(ctx->rPriv);
+   struct st_api *stapi = screen->st_api;
 
    if (--ctx->bind_count == 0) {
       if (ctx->st == ctx->stapi->get_current(ctx->stapi)) {
          ctx->st->flush(ctx->st, PIPE_FLUSH_RENDER_CACHE, NULL);
-         ctx->stapi->make_current(ctx->stapi, NULL, NULL, NULL);
+         stapi->make_current(stapi, NULL, NULL, NULL);
+         draw->context = NULL;
+         read->context = NULL;
       }
    }
 
@@ -174,10 +180,12 @@ dri_make_current(__DRIcontext * cPriv,
    else if (!driDrawPriv || !driReadPriv)
       return GL_FALSE;
 
+   draw->context = ctx;
    if (ctx->dPriv != driDrawPriv) {
       ctx->dPriv = driDrawPriv;
       draw->texture_stamp = driDrawPriv->lastStamp - 1;
    }
+   read->context = ctx;
    if (ctx->rPriv != driReadPriv) {
       ctx->rPriv = driReadPriv;
       read->texture_stamp = driReadPriv->lastStamp - 1;

src/gallium/state_trackers/dri/common/dri_drawable.c

@@ -132,6 +132,7 @@ dri_create_buffer(__DRIscreen * sPriv,
    drawable->base.validate = dri_st_framebuffer_validate;
    drawable->base.st_manager_private = (void *) drawable;
 
+   drawable->screen = screen;
    drawable->sPriv = sPriv;
    drawable->dPriv = dPriv;
    dPriv->driverPrivate = (void *)drawable;

src/gallium/state_trackers/dri/common/dri_drawable.h

@@ -41,6 +41,9 @@ struct dri_drawable
    struct st_framebuffer_iface base;
    struct st_visual stvis;
 
+   struct dri_screen *screen;
+   struct dri_context *context;
+
    /* dri */
    __DRIdrawable *dPriv;
    __DRIscreen *sPriv;

src/gallium/state_trackers/dri/drm/dri2.c

@@ -52,7 +52,7 @@ static void
 dri2_invalidate_drawable(__DRIdrawable *dPriv)
 {
    struct dri_drawable *drawable = dri_drawable(dPriv);
-   struct dri_context *ctx = dri_context(dPriv->driContextPriv);
+   struct dri_context *ctx = drawable->context;
 
    dri2InvalidateDrawable(dPriv);
    drawable->dPriv->lastStamp = *drawable->dPriv->pStamp;