From mboxrd@z Thu Jan  1 00:00:00 1970
From: Ben Widawsky <ben@bwidawsk.net>
Subject: Re: [PATCH] drm/i915: ioctl to query a bo's cache level
Date: Thu, 22 Sep 2011 15:36:51 +0000
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To: Daniel Vetter <daniel@ffwll.ch>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>, intel-gfx@lists.freedesktop.org
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On Thu, Sep 22, 2011 at 09:35:12AM +0200, Daniel Vetter wrote:
> On Wed, Sep 21, 2011 at 06:47:10PM -0700, Ben Widawsky wrote:
> > diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
> > index a546a71..362da16 100644
> > --- a/drivers/gpu/drm/i915/i915_gem.c
> > +++ b/drivers/gpu/drm/i915/i915_gem.c
> > @@ -3777,6 +3777,29 @@ void i915_gem_free_object(struct drm_gem_object *gem_obj)
> >  }
> >  
> >  int
> > +i915_gem_get_cache_type_ioctl(struct drm_device *dev, void *data,
> > +			      struct drm_file *file_priv)
> > +{
> > +
> > +	struct drm_i915_gem_get_cache_type *args = data;
> > +	struct drm_i915_gem_object *obj;
> > +	int ret = 0;
> > +
> > +	obj = to_intel_bo(drm_gem_object_lookup(dev, file_priv, args->handle));
> > +	if (&obj->base == NULL) {
> > +		ret = -ENOENT;
> > +		goto out;
> > +	}
> > +
> > +	args->cache_level = obj->cache_level;
> 
> Grab struct_mutex around this, obj->cache_level might change over the
> lifetime of the bo. Yeah, our locking is a mess, I know ;-)

I don't see how a lock by itself helps. The cache_level could change as soon as
you release the lock which results in the same problem.

Ben