Radeon/dmabuf - crash when dmabuf buffers are mapped/unmapped from various threads

Fedora 33 / mesa-dri-drivers-20.3.4-2.fc33.x86_64

I'm experiencing crashes in mesa-dri code (u_threaded_context.c) while multiple dmabuf buffers are mapped/unmapped from various threads. This happens when video is decoded to multiple dmabuf buffers.

Backtrace is available here: https://bugzilla.mozilla.org/show_bug.cgi?id=1661572#c11

This is clearly reproducible on radeon drivers only, I can't reproduce it on Intel drivers.