https://bugzilla.kernel.org/show_bug.cgi?id=87791
--- Comment #5 from aCaB acab@digitalfuture.it --- Michel, Thanks for your pointer and sorry for the late answer.
I'll try harder to find a reproducible case (firefox with some large animation seems to trigger it some times). In the meantime, if the lockup is a mesa bug then feel free to close this ticket.