[Bug 100858] [SNB] igt at drv_module_reload@basic-reload-final fails and hard hangs the system

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=100858

--- Comment #2 from krisman at collabora.co.uk ---
(In reply to Chris Wilson from comment #1)
> The answer lies in if the GPU didn't write the dword to where we wanted,
> where did it write it? And the same worrying question will be for lots of
> different ops. The HWS is intact otherwise it would have complained about a
> gpu hang... Actually no, that test isn't checking so that's a more
> reasonable explanation that the HWS write also went astray, i.e. it is
> likely that nothing is right in the way the GPU is addressing memory.
> 
> In load/unload we do a GPU reset, so everything should be sane...
> 
> Remove the store dword check and see it it still hard hangs. If so, we can
> start removing chunks from the load/unload sequence and see at what point it
> works.

It doesn't hard hang without the store_dword sequence.  The hang happens on
gem_write when executing the blt engine.  One interesting aspect is that the
issue is only reproducible with intel_iommu=on.  If that parameter is disabled,
the test succeeds and the system never hangs.

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