[Bug 103304] multi-threaded usage of Gallium RadeonSI leads to NULL pointer exception in pb_cache_reclaim_buffer

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=103304

--- Comment #3 from Nicolai Hähnle <nhaehnle at gmail.com> ---
After thinking about it some more, I think it's very likely that your
application also has a bug, a write-after-read bug to be precise.

What I'm suspecting is that you're doing this:

  Thread 1              Thread 2
  --------              --------
  glBindTexture(tex);
  glDraw*(...);
  glFlush();
                        glTextureSubImage(tex, ...);

Unless you use glFinish() or glFenceSync() / glWaitSync() synchronization,
there is no guarantee that thread 1's draw has completed before thread 2's
texture change. In other words, the implementation is allowed to execute the
texture modification *before* the draw. Especially with Gallium threading, this
is quite likely to happen.

(We still also have a bug in the driver, but until I can actually double-check
your code, I'd say it's quite likely that you have a write-after-read hazard
like the one explained above.)

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