Re: [Intel-gfx] [PATCH i-g-t] lib/i915/gem_engine_topology.c - intel_get_current_engine invalid result

[Chris Wilson <chris@chris-wilson.co.uk>]

Quoting Antonio Argenziano (2020-02-14 18:43:01)
> 
> 
> On 13/02/20 11:26, Dale B Stimson wrote:
> > Function intel_get_current_engine() should return NULL (instead of
> > engine 0) if there are no engines.
> > 
> > Function intel_init_engine_list() should not store potential engine
> > data in the output structure unless the engine is present.
> > 
> > Function intel_init_engine_list() should arguably not filter the static
> > engine list with gem_has_ring if fd == -1, so that subtests can still
> > be individually invoked to show subtest FAIL instead of test notrun.
> > 
> > Symptom: A device open failure in gem_ctx_isolation resulted in
> > an endless __for_each_physical_engine "per-engine" loop with the
> > purported last potential engine being processed every time.
> > 
> > Diagnosis: device open (or debugfs open) failed, leaving fd == -1.
> > Control skipped the rest of the initial igt_fixture block, after
> > which an attempt was made to iterate through engines using macro
> > __for_each_physical_engine.
> > 
> > Macro __for_each_physical_engine called intel_init_engine_list()
> > to initialize the loop control data.  Because fd == -1,
> > intel_init_engine_list() fell back to using __for_each_static_engine().
> > All of the engines in the static engine list are rejected due to
> > gem_has_ring returning false (because of fd == -1), leaving 0 engines.
> > That resulted in loop control data with engine_data.nengines == 0
> > and the data for the last engine considered stored at index 0.
> > 
> > Still in macro __for_each_physical_engine, intel_get_current_engine()
> > was called to get the engine to process.  It should have returned NULL,
> > but instead returned the engine entry at index 0, which
> > had received information describing the last potential engine.
> > This happened without end.
> > 
> > Signed-off-by: Dale B Stimson <dale.b.stimson@intel.com>
> > ---
> >   lib/i915/gem_engine_topology.c | 29 ++++++++++++++++-------------
> >   1 file changed, 16 insertions(+), 13 deletions(-)
> > 
> > diff --git a/lib/i915/gem_engine_topology.c b/lib/i915/gem_engine_topology.c
> > index 9daa03df4..b8ed49bc9 100644
> > --- a/lib/i915/gem_engine_topology.c
> > +++ b/lib/i915/gem_engine_topology.c
> > @@ -156,10 +156,10 @@ static void query_engine_list(int fd, struct intel_engine_data *ed)
> >   struct intel_execution_engine2 *
> >   intel_get_current_engine(struct intel_engine_data *ed)
> >   {
> > -     if (!ed->n)
> > -             ed->current_engine = &ed->engines[0];
> > -     else if (ed->n >= ed->nengines)
> > +     if (ed->n >= ed->nengines)
> >               ed->current_engine = NULL;
> > +     else if (!ed->n)
> > +             ed->current_engine = &ed->engines[0];
> >   
> >       return ed->current_engine;
> >   }
> > @@ -222,18 +222,21 @@ struct intel_engine_data intel_init_engine_list(int fd, uint32_t ctx_id)
> >               igt_debug("using pre-allocated engine list\n");
> >   
> >               __for_each_static_engine(e2) {
> > -                     struct intel_execution_engine2 *__e2 =
> > -                             &engine_data.engines[engine_data.nengines];
> > -
> > -                     strcpy(__e2->name, e2->name);
> > -                     __e2->instance   = e2->instance;
> > -                     __e2->class      = e2->class;
> > -                     __e2->flags      = e2->flags;
> > -                     __e2->is_virtual = false;
> > -
> >                       if (igt_only_list_subtests() ||
> > -                         gem_has_ring(fd, e2->flags))
> > +                         (fd < 0) ||
> 
> Patch LGTM, Chris do you have any issues merging this before someone 
> implements some tests for the infrastructure?

It seems like a really trivial one to write a test for. 3 minutes
tops... Just do it.
-Chris
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