Re: [PATCH] drm/i915/selftests: Allow engine reset failure to do a GT reset in hangcheck selftest

[Thomas Hellström <thomas.hellstrom@xxxxxxxxxxxxxxx>]

On 10/21/21 22:37, Matthew Brost wrote:
> On Thu, Oct 21, 2021 at 08:15:49AM +0200, Thomas Hellström wrote:
> > Hi, Matthew,
> >
> > On Mon, 2021-10-11 at 16:47 -0700, Matthew Brost wrote:
> > > The hangcheck selftest blocks per engine resets by setting magic bits
> > > in
> > > the reset flags. This is incorrect for GuC submission because if the
> > > GuC
> > > fails to reset an engine we would like to do a full GT reset. Do no
> > > set
> > > these magic bits when using GuC submission.
> > >
> > > Side note this lockless algorithm with magic bits to block resets
> > > really
> > > should be ripped out.
> > Lockless algorithm aside, from a quick look at the code in
> > intel_reset.c it appears to me like the interface that falls back to a
> > full GT reset is intel_gt_handle_error() whereas intel_engine_reset()
> > is explicitly intended to not do that, so is there a discrepancy
> > between GuC and non-GuC here?
> With GuC submission when an engine reset fails, we get an engine reset
> failure notification which triggers a full GT reset
> (intel_guc_engine_failure_process_msg in intel_guc_submission.c). That
> reset is blocking by setting these magic bits. Clearing the bits in this
> function doesn't seem to unblock that reset either, the driver tries to
> unload with a worker blocked, and results in the blow up. Something with
> this lockless algorithm could be wrong as clear of the bit should
> unlblock the reset but it is doesn't. We can look into that but in the
> meantime we need to fix this test to be able to fail gracefully and not
> crash CI.

Yeah, for that lockless algorithm if needed, we might want to use a 
ww_mutex per engine or something,
but point was that AFAICT at least one of the tests that set those flags 
explicitly tested the functionality that no other engines than the 
intended one was reset when the intel_engine_reset() function was used, 
and then if GuC submission doesn't honor that, wouldn't a better 
approach be to make a code comment around intel_engine_reset() to 
explain the differences and disable that particular test for GuC?. Also 
wouldn't we for example we see a duplicated full GT reset with GuC if 
intel_engine_reset() fails as part of the intel_gt_handle_error() function?

I guess we could live with the hangcheck test being disabled for guc 
submission until this is sorted out?

/Thomas


> Matt
>
> > /Thomas
> >
> >
> > > Signed-off-by: Matthew Brost <matthew.brost@xxxxxxxxx>
> > > ---
> > >   drivers/gpu/drm/i915/gt/selftest_hangcheck.c | 12 ++++++++----
> > >   1 file changed, 8 insertions(+), 4 deletions(-)
> > >
> > > diff --git a/drivers/gpu/drm/i915/gt/selftest_hangcheck.c
> > > b/drivers/gpu/drm/i915/gt/selftest_hangcheck.c
> > > index 7e2d99dd012d..90a03c60c80c 100644
> > > --- a/drivers/gpu/drm/i915/gt/selftest_hangcheck.c
> > > +++ b/drivers/gpu/drm/i915/gt/selftest_hangcheck.c
> > > @@ -734,7 +734,8 @@ static int __igt_reset_engine(struct intel_gt
> > > *gt, bool active)
> > >                  reset_engine_count = i915_reset_engine_count(global,
> > > engine);
> > >   
> > >                  st_engine_heartbeat_disable(engine);
> > > -               set_bit(I915_RESET_ENGINE + id, &gt->reset.flags);
> > > +               if (!using_guc)
> > > +                       set_bit(I915_RESET_ENGINE + id, &gt-
> > > > reset.flags);
> > >                  count = 0;
> > >                  do {
> > >                          struct i915_request *rq = NULL;
> > > @@ -824,7 +825,8 @@ static int __igt_reset_engine(struct intel_gt
> > > *gt, bool active)
> > >                          if (err)
> > >                                  break;
> > >                  } while (time_before(jiffies, end_time));
> > > -               clear_bit(I915_RESET_ENGINE + id, &gt->reset.flags);
> > > +               if (!using_guc)
> > > +                       clear_bit(I915_RESET_ENGINE + id, &gt-
> > > > reset.flags);
> > >                  st_engine_heartbeat_enable(engine);
> > >                  pr_info("%s: Completed %lu %s resets\n",
> > >                          engine->name, count, active ? "active" :
> > > "idle");
> > > @@ -1042,7 +1044,8 @@ static int __igt_reset_engines(struct intel_gt
> > > *gt,
> > >                  yield(); /* start all threads before we begin */
> > >   
> > >                  st_engine_heartbeat_disable_no_pm(engine);
> > > -               set_bit(I915_RESET_ENGINE + id, &gt->reset.flags);
> > > +               if (!using_guc)
> > > +                       set_bit(I915_RESET_ENGINE + id, &gt-
> > > > reset.flags);
> > >                  do {
> > >                          struct i915_request *rq = NULL;
> > >                          struct intel_selftest_saved_policy saved;
> > > @@ -1165,7 +1168,8 @@ static int __igt_reset_engines(struct intel_gt
> > > *gt,
> > >                          if (err)
> > >                                  break;
> > >                  } while (time_before(jiffies, end_time));
> > > -               clear_bit(I915_RESET_ENGINE + id, &gt->reset.flags);
> > > +               if (!using_guc)
> > > +                       clear_bit(I915_RESET_ENGINE + id, &gt-
> > > > reset.flags);
> > >                  st_engine_heartbeat_enable_no_pm(engine);
> > >   
> > >                  pr_info("i915_reset_engine(%s:%s): %lu resets\n",