Re: [PATCH 5/9] drm/i915/guc: Flush the work queue for GuC generated G2H

[Daniel Vetter <daniel@ffwll.ch>]

On Thu, Aug 12, 2021 at 03:23:30PM +0000, Matthew Brost wrote:
> On Thu, Aug 12, 2021 at 04:11:28PM +0200, Daniel Vetter wrote:
> > On Wed, Aug 11, 2021 at 01:16:18AM +0000, Matthew Brost wrote:
> > > Flush the work queue for GuC generated G2H messages durinr a GT reset.
> > > This is accomplished by spinning on the the list of outstanding G2H to
> > > go empty.
> > > 
> > > Fixes: eb5e7da736f3 ("drm/i915/guc: Reset implementation for new GuC interface")
> > > Signed-off-by: Matthew Brost <matthew.brost@intel.com>
> > > Cc: <stable@vger.kernel.org>
> > > ---
> > >  drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c | 5 +++++
> > >  1 file changed, 5 insertions(+)
> > > 
> > > diff --git a/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c b/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
> > > index 3cd2da6f5c03..e5eb2df11b4a 100644
> > > --- a/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
> > > +++ b/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
> > > @@ -727,6 +727,11 @@ void intel_guc_submission_reset_prepare(struct intel_guc *guc)
> > >  			wait_for_reset(guc, &guc->outstanding_submission_g2h);
> > >  		} while (!list_empty(&guc->ct.requests.incoming));
> > >  	}
> > > +
> > > +	/* Flush any GuC generated G2H */
> > > +	while (!list_empty(&guc->ct.requests.incoming))
> > > +		msleep(20);
> > 
> > flush_work or flush_workqueue, beacuse that comes with lockdep
> > annotations. Dont hand-roll stuff like this if at all possible.
> 
> lockdep puked when used that.

Lockdep tends to be right ... So we definitely want that, but maybe a
different flavour, or there's something wrong with the workqueue setup.

This is the major reason why inventing any wheels locally in the kernel
isn't a good idea - aside from the duplicated code because likely there is
a solution for whatever you need. There's all the validation tools,
careful thought about semantics (especially around races) and all that
stuff that you're always missing on your hand-rolled thing. Aside from
anything hand-rolled is much harder to read, since intent isn't clear.
-Daniel


> 
> Matt
> 
> > -Daniel
> > 
> > > +
> > >  	scrub_guc_desc_for_outstanding_g2h(guc);
> > >  }
> > >  
> > > -- 
> > > 2.32.0
> > > 
> > 
> > -- 
> > Daniel Vetter
> > Software Engineer, Intel Corporation
> > http://blog.ffwll.ch

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch