Quoting Mika Kuoppala (2019-02-08 14:47:13)
> Chris Wilson <[email protected]> writes:
>
> > If we haven't even begun executing the payload of the stalled request,
> > then we should not claim that its userspace context was guilty of
> > submitting a hanging batch.
> >
> > v2: Check for context corruption before trying to restart.
> > v3: Preserve semaphores on skipping requests (need to keep the timelines
> > intact).
> >
> > Signed-off-by: Chris Wilson <[email protected]>
> > ---
> > drivers/gpu/drm/i915/intel_lrc.c | 42 +++++++++++++++++--
> > drivers/gpu/drm/i915/selftests/igt_spinner.c | 9 +++-
> > .../gpu/drm/i915/selftests/intel_hangcheck.c | 6 +++
> > 3 files changed, 53 insertions(+), 4 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/i915/intel_lrc.c
> > b/drivers/gpu/drm/i915/intel_lrc.c
> > index 5e98fd79bd9d..e3134a635926 100644
> > --- a/drivers/gpu/drm/i915/intel_lrc.c
> > +++ b/drivers/gpu/drm/i915/intel_lrc.c
> > @@ -1387,6 +1387,10 @@ static int gen8_emit_init_breadcrumb(struct
> > i915_request *rq)
> > *cs++ = rq->fence.seqno - 1;
> >
> > intel_ring_advance(rq, cs);
> > +
> > + /* Record the updated position of the request's payload */
> > + rq->infix = intel_ring_offset(rq, cs);
> > +
> > return 0;
> > }
> >
> > @@ -1878,6 +1882,23 @@ static void execlists_reset_prepare(struct
> > intel_engine_cs *engine)
> > spin_unlock_irqrestore(&engine->timeline.lock, flags);
> > }
> >
> > +static bool lrc_regs_ok(const struct i915_request *rq)
> > +{
> > + const struct intel_ring *ring = rq->ring;
> > + const u32 *regs = rq->hw_context->lrc_reg_state;
> > +
> > + /* Quick spot check for the common signs of context corruption */
> > +
> > + if (regs[CTX_RING_BUFFER_CONTROL + 1] !=
> > + (RING_CTL_SIZE(ring->size) | RING_VALID))
> > + return false;
>
> You been noticing this with ctx corruption? Well now
> thinking about it, we have had reports where on init,
> on some trouble, the valid vanishes.
Yes, it's why we've been copying the default context over guilty for a
long time (pretty much since live_hangcheck became a thing iirc).
> > +
> > + if (regs[CTX_RING_BUFFER_START + 1] != i915_ggtt_offset(ring->vma))
> > + return false;
> > +
>
> Seen this on bugzilla reports too. Are there more
> in your sleeve or is this a compromise on complexity
> and performance? Checking on a sane actual head too?
No, I can't remember seeing this, just loosing CTL. But I do recall that
at one point it seemed the whole reg state was zero, but that is foggy
memory.
> The heuristics of it bothers me some as we will
> get false positives.
They cannot be false positives! If we restore to a batch setup like
this, it will hang -- which is why we explicitly reset them.
> So in effect, when we get one, we just move ahead
> after an extra reset as we got it all wrong?
Yup. The context is corrupt, we replace it with a sane one and hope
nobody notices. Mesa does notice though....
> > + return true;
> > +}
> > +
> > static void execlists_reset(struct intel_engine_cs *engine, bool stalled)
> > {
> > struct intel_engine_execlists * const execlists = &engine->execlists;
> > @@ -1912,6 +1933,21 @@ static void execlists_reset(struct intel_engine_cs
> > *engine, bool stalled)
> > if (!rq)
> > goto out_unlock;
> >
> > + /*
> > + * If this request hasn't started yet, e.g. it is waiting on a
> > + * semaphore, we need to avoid skipping the request or else we
> > + * break the signaling chain. However, if the context is corrupt
> > + * the request will not restart and we will be stuck with a wedged
> > + * device. It is quite often the case that if we issue a reset
> > + * while the GPU is loading the context image, that context image
> > + * becomes corrupt.
> > + *
> > + * Otherwise, if we have not started yet, the request should replay
> > + * perfectly and we do not need to flag the result as being erroneous.
> > + */
> > + if (!i915_request_started(rq) && lrc_regs_ok(rq))
> > + goto out_unlock;
> > +
> > /*
> > * If the request was innocent, we leave the request in the ELSP
> > * and will try to replay it on restarting. The context image may
> > @@ -1924,7 +1960,7 @@ static void execlists_reset(struct intel_engine_cs
> > *engine, bool stalled)
> > * image back to the expected values to skip over the guilty request.
> > */
> > i915_reset_request(rq, stalled);
> > - if (!stalled)
> > + if (!stalled && lrc_regs_ok(rq))
>
> Extend the ctx validator usage for on guilty engines, well why not.
We forcibly reset anyway.
-Chris
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