[Intel-gfx] [PATCH v2] drm/i915: Stop automatically retiring requests after a GPU hang

[Chris Wilson]

On Fri, May 13, 2016 at 11:43:25AM +0300, Mika Kuoppala wrote:
> Chris Wilson <chris at chris-wilson.co.uk> writes:
> 
> > [ text/plain ]
> > Following a GPU hang, we break out of the request loop in order to
> > unlock the struct_mutex for use by the GPU reset. However, if we retire
> > all the requests at that moment, we cannot identify the guilty request
> > after performing the reset.
> >
> > v2: Not automatically retiring requests forces us to recheck for
> > available ringspace.
> >
> > Fixes: f4457ae71fd6 ("drm/i915: Prevent leaking of -EIO from
> > i915_wait_request()")
> 
> Partially. We don't clear the request list before reset
> processing. But we still do release clients before reset
> processing. This leads to clients see completed
> requests before the reset statistics have been updated.
> 
> If we return -EAGAIN in wait_request, then we unblock
> the clients only until the reset handling has updated
> the seqno past the reset boundary. This would fix
> both issues I am seeing.

I am very wary about reintroducing -EAGAIN here, since the majority of
callers do not care - or worse do not handle such notifications and
would be confused by it (the request they waited upon is no more and
they are ready to continue after all).

Anyway, the bug looks to be on the other side here as the
get-reset-stats ioctl doesn't wait for a pending reset before reporting
victim/guilty counts.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre