On Wed, Mar 15, 2017 at 09:23:01AM +0000, Tvrtko Ursulin wrote:
>
> On 14/03/2017 09:34, Chris Wilson wrote:
> >When we wedge the device, we override engine->submit_request with a nop
> >to ensure that all in-flight requests are marked in error. However, igt
> >would like to unwedge the device to test -EIO handling. This requires us
> >to flush those in-flight requests and restore the original
> >engine->submit_request.
> >
> >v2: Use a vfunc to unify enabling request submission to engines
> >v3: Split new vfunc to a separate patch.
> >
> >Fixes: 821ed7df6e2a ("drm/i915: Update reset path to fix incomplete requests")
> >Testcase: igt/gem_eio
> >Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
> >Cc: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>
> >Cc: Mika Kuoppala <mika.kuoppala@xxxxxxxxx>
> >---
> > drivers/gpu/drm/i915/i915_drv.c | 2 +-
> > drivers/gpu/drm/i915/i915_drv.h | 1 +
> > drivers/gpu/drm/i915/i915_gem.c | 51 +++++++++++++++++++++++++++++++++++++++++
> > 3 files changed, 53 insertions(+), 1 deletion(-)
> >
> >diff --git a/drivers/gpu/drm/i915/i915_drv.c b/drivers/gpu/drm/i915/i915_drv.c
> >index e312b61ba6bb..11d1066b673c 100644
> >--- a/drivers/gpu/drm/i915/i915_drv.c
> >+++ b/drivers/gpu/drm/i915/i915_drv.c
> >@@ -1822,7 +1822,7 @@ void i915_reset(struct drm_i915_private *dev_priv)
> > return;
> >
> > /* Clear any previous failed attempts at recovery. Time to try again. */
> >- __clear_bit(I915_WEDGED, &error->flags);
> >+ i915_gem_unset_wedged(dev_priv);
> > error->reset_count++;
> >
> > pr_notice("drm/i915: Resetting chip after gpu hang\n");
> >diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
> >index 48ff64812289..53a791d8d992 100644
> >--- a/drivers/gpu/drm/i915/i915_drv.h
> >+++ b/drivers/gpu/drm/i915/i915_drv.h
> >@@ -3406,6 +3406,7 @@ int i915_gem_reset_prepare(struct drm_i915_private *dev_priv);
> > void i915_gem_reset(struct drm_i915_private *dev_priv);
> > void i915_gem_reset_finish(struct drm_i915_private *dev_priv);
> > void i915_gem_set_wedged(struct drm_i915_private *dev_priv);
> >+void i915_gem_unset_wedged(struct drm_i915_private *dev_priv);
> >
> > void i915_gem_init_mmio(struct drm_i915_private *i915);
> > int __must_check i915_gem_init(struct drm_i915_private *dev_priv);
> >diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
> >index 202bb850f260..e06830916a05 100644
> >--- a/drivers/gpu/drm/i915/i915_gem.c
> >+++ b/drivers/gpu/drm/i915/i915_gem.c
> >@@ -3000,6 +3000,57 @@ void i915_gem_set_wedged(struct drm_i915_private *dev_priv)
> > mod_delayed_work(dev_priv->wq, &dev_priv->gt.idle_work, 0);
> > }
> >
> >+void i915_gem_unset_wedged(struct drm_i915_private *i915)
> >+{
> >+ struct i915_gem_timeline *tl;
> >+ int i;
> >+
> >+ lockdep_assert_held(&i915->drm.struct_mutex);
> >+ if (!test_bit(I915_WEDGED, &i915->gpu_error.flags))
> >+ return;
> >+
> >+ /* Before unwedging, make sure that all pending operations
> >+ * are flushed and errored out. No more can be submitted until
> >+ * we reset the wedged bit.
> >+ */
> >+ list_for_each_entry(tl, &i915->gt.timelines, link) {
> >+ for (i = 0; i < ARRAY_SIZE(tl->engine); i++) {
> >+ struct drm_i915_gem_request *rq;
> >+
> >+ rq = i915_gem_active_peek(&tl->engine[i].last_request,
> >+ &i915->drm.struct_mutex);
> >+ if (!rq)
> >+ continue;
> >+
> >+ /* We can't use our normal waiter as we want to
> >+ * avoid recursively trying to handle the current
> >+ * reset. The basic dma_fence_default_wait() installs
> >+ * a callback for dma_fence_signal(), which is
> >+ * triggered by our nop handler (indirectly, the
> >+ * callback enables the signaler thread which is
> >+ * woken by the nop_submit_request() advancing the seqno
> >+ * and when the seqno passes the fence, the signaler
> >+ * then signals the fence waking us up).
> >+ */
> >+ dma_fence_default_wait(&rq->fence, false,
> >+ MAX_SCHEDULE_TIMEOUT);
> >+ }
> >+ }
> >+
> >+ /* Undo nop_submit_request. We prevent all new i915 requests from
> >+ * being queued (by disallowing execbuf whilst wedged) so having
> >+ * waited for all active requests above, we know the system is idle
> >+ * and do not have to worry about a thread being inside
> >+ * engine->submit_request() as we swap over. So unlike installing
> >+ * the nop_submit_request on reset, we can do this from normal
> >+ * context and do not require stop_machine().
> >+ */
> >+ intel_engines_enable_submission(i915);
>
> So the point of the dma_fence_default_wait above is it to ensure all
> nop_submit_request call backs have completed? I don't at the moment
> understand how could there be such callbacks since unwedge is
> happening after the wedge. So the wedge already installed the nop
> handler, and by the time we get to another reset attempt, isn't it
> already guaranteed all of those have exited?
There's no such guarantee. The nop_submit_request() is to ensure that all
third party driven requests are flushed and our requests are marked with
dma_fence_set_error(-EIO) and not submitted to hw.
-Chris
--
Chris Wilson, Intel Open Source Technology Centre
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