piglits arb_framebuffer_no_attachments-atomic are flaky
The piglits are randomly passing and failing on llvmpipe they are more likely to fail, and on radeonsi the always seem to pass, at least with vtest.
Printing out the atomic buffer content that is read back on the host indicates that the host executes the GL program correctly, and the actual problem seems to be with the host-guest synchronization. This hypothesis is supported by the fact that adding a sleep(1)
at the location where the buffer is read back on the host makes the tests pass.