[Intel-gfx] [PATCH 2/5] drm: Allow determining if current task is output poll worker

Lukas Wunner lukas at wunner.de
Mon Feb 12 18:40:06 UTC 2018


On Mon, Feb 12, 2018 at 05:50:12PM +0000, Chris Wilson wrote:
> Quoting Lyude Paul (2018-02-12 17:46:11)
> > On Sun, 2018-02-11 at 10:38 +0100, Lukas Wunner wrote:
> > > Introduce a helper to determine if the current task is an output poll
> > > worker.
> > > 
> > > This allows us to fix a long-standing deadlock in several DRM drivers
> > > wherein the ->runtime_suspend callback waits for the output poll worker
> > > to finish and the worker in turn calls a ->detect callback which waits
> > > for runtime suspend to finish.  The ->detect callback is invoked from
> > > multiple call sites and waiting for runtime suspend to finish is the
> > > correct thing to do except if it's executing in the context of the
> > > worker.
> > > 
> > > Cc: Dave Airlie <airlied at redhat.com>
> > > Cc: Ben Skeggs <bskeggs at redhat.com>
> > > Cc: Alex Deucher <alexander.deucher at amd.com>
> > > Signed-off-by: Lukas Wunner <lukas at wunner.de>
> > > ---
> > >  drivers/gpu/drm/drm_probe_helper.c | 14 ++++++++++++++
> > >  include/drm/drm_crtc_helper.h      |  1 +
> > >  2 files changed, 15 insertions(+)
> > > 
> > > diff --git a/drivers/gpu/drm/drm_probe_helper.c
> > > b/drivers/gpu/drm/drm_probe_helper.c
> > > index 555fbe54d6e2..019881d15ce1 100644
> > > --- a/drivers/gpu/drm/drm_probe_helper.c
> > > +++ b/drivers/gpu/drm/drm_probe_helper.c
> > > @@ -653,6 +653,20 @@ static void output_poll_execute(struct work_struct
> > > *work)
> > >               schedule_delayed_work(delayed_work,
> > > DRM_OUTPUT_POLL_PERIOD);
> > >  }
> > >  
> > > +/**
> > > + * drm_kms_helper_is_poll_worker - is %current task an output poll worker?
> > > + *
> > > + * Determine if %current task is an output poll worker.  This can be used
> > > + * to select distinct code paths for output polling versus other contexts.
> > > + */
> > > +bool drm_kms_helper_is_poll_worker(void)
> > > +{
> > > +     struct work_struct *work = current_work();
> > > +
> > > +     return work && work->func == output_poll_execute;
> 
> What ensures that work is accessible? Does this need rcu_read_lock
> protection or more?

The work_struct exists as long this kthread is working on it.
Since this is called by the kthread itself, it is guaranteed to exist.
So there's no protection needed.

Thanks,

Lukas


More information about the dri-devel mailing list