[Mesa-dev] Using the right context in st_texture_release_all_sampler_views()

[Jose Fonseca]

On 22/07/15 23:32, Brian Paul wrote:
> Hi Marek,
>
> This is regarding your commit "st/mesa: use pipe_sampler_view_release
> for releasing sampler views" from last October.
>
> Basically, we have:
>
> void
> st_texture_release_all_sampler_views(struct st_context *st,
>                                       struct st_texture_object *stObj)
> {
>     GLuint i;
>
>     /* XXX This should use sampler_views[i]->pipe, not st->pipe */
>     for (i = 0; i < stObj->num_sampler_views; ++i)
>        pipe_sampler_view_release(st->pipe, &stObj->sampler_views[i]);
> }
>
> Our VMware/svga driver has an issue when
> pipe_context::sampler_view_destroy() is called with one context and a
> sampler view which was created with another context.  I can hack around
> it in our driver code, but it would be nice to fix this in the state
> tracker.
>
> Ideally, the above code should be something like:
>
>     for (i = 0; i < stObj->num_sampler_views; ++i)
>        pipe_sampler_view_reference(&stObj->sampler_views[i], NULL);
>
> The current code which uses the st->pipe context came from the bug
> https://bugs.freedesktop.org/show_bug.cgi?id=81680
>
> AFAICT, you were just working around an R600 driver issue.  Any chance
> we could fix the state tracker and re-test Firefox on R600?

Freeing a view from a different context with another context is wrong.

But freeing a view with a context that might be current on another 
thread is also wrong, as pipe_context are not thread safe.


If that was the previous behavior, then maybe Firefox crashed due to the 
race conditions.  Looking at the stack trace, I suspect that what 
happened was that one context was freeing the st_texture, and all its 
views, while the other context was destroying itself, and all its own 
views.  In short, st_texture_release_sampler_view was being called 
simultanouesly from two different threads.


The proper fix IMO is to let the pipe context that owns the view to 
destroyed from whatever thread it is current (or whenever it is made 
current.)


Jose