[PATCH] drm: vc4: Fix race during binding

[Stefan Wahren]

Hi Eric,

> Eric Anholt <eric at anholt.net> hat am 6. Oktober 2017 um 21:42 geschrieben:
> 
> 
> Stefan Wahren <stefan.wahren at i2se.com> writes:
> 
> > This fixes the race between vc4_overflow_mem_work and the init of the
> > job lock. Otherwise we could trigger a NULL pointer dereference
> > during VC4 binding.
> >
> > Link: https://github.com/anholt/linux/issues/114
> > Signed-off-by: Stefan Wahren <stefan.wahren at i2se.com>
> > Fixes: d5b1a78a772f ("drm/vc4: Add support for drawing 3D frames.")
> > ---
> >  drivers/gpu/drm/vc4/vc4_gem.c | 1 -
> >  drivers/gpu/drm/vc4/vc4_irq.c | 1 +
> >  2 files changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/gpu/drm/vc4/vc4_gem.c b/drivers/gpu/drm/vc4/vc4_gem.c
> > index d0c6bfb..47d964f 100644
> > --- a/drivers/gpu/drm/vc4/vc4_gem.c
> > +++ b/drivers/gpu/drm/vc4/vc4_gem.c
> > @@ -1088,7 +1088,6 @@ vc4_gem_init(struct drm_device *dev)
> >  	INIT_LIST_HEAD(&vc4->render_job_list);
> >  	INIT_LIST_HEAD(&vc4->job_done_list);
> >  	INIT_LIST_HEAD(&vc4->seqno_cb_list);
> > -	spin_lock_init(&vc4->job_lock);
> >  
> >  	INIT_WORK(&vc4->hangcheck.reset_work, vc4_reset_work);
> >  	setup_timer(&vc4->hangcheck.timer,
> > diff --git a/drivers/gpu/drm/vc4/vc4_irq.c b/drivers/gpu/drm/vc4/vc4_irq.c
> > index 7d7af3a..d508d13 100644
> > --- a/drivers/gpu/drm/vc4/vc4_irq.c
> > +++ b/drivers/gpu/drm/vc4/vc4_irq.c
> > @@ -195,6 +195,7 @@ vc4_irq_preinstall(struct drm_device *dev)
> >  	struct vc4_dev *vc4 = to_vc4_dev(dev);
> >  
> >  	init_waitqueue_head(&vc4->job_wait_queue);
> > +	spin_lock_init(&vc4->job_lock);
> >  	INIT_WORK(&vc4->overflow_mem_work, vc4_overflow_mem_work);
> >  
> >  	/* Clear any pending interrupts someone might have left around
> 
> Are you sure this is a fix?  We don't attach the IRQ handler until V3D
> bind, and vc4_gem_init happens before component_bind_all(), right?

i agree i should have mark it as a RFC. But is it really impossible that vc4_overflow_mem_work is triggered before vc4_gem_init?