Re: [PATCH] drm/i915: Fix list corruption in vma_unbind

[Daniel Vetter <daniel@ffwll.ch>]

On Thu, Aug 29, 2013 at 07:57:38PM +0100, Chris Wilson wrote:
> On Thu, Aug 29, 2013 at 07:50:31PM +0200, Daniel Vetter wrote:
> > The saga around the breadcrumb vmas used by execbuf continues ...
> > 
> > This time around we've managed to unconditionally move the object to
> > the unbound list on the last vma unbind even though it might never
> > have been on either the bound or unbound list. Hilarity ensued.
> > 
> > Chris Wilson tracked this one down but compared to his patches I've
> > simply opted to completely separate the unbound case for not-yet bound
> > vmas. Otherwise we imo end up with semantically hard to parse checks
> > around the list_move_tail(global_list, ...).
> > 
> > This is exercised by the new swapping variants of
> > igt/tests/gem_evict_everything.
> > 
> > Cc: Chris Wilson <chris@chris-wilson.co.uk>
> > Cc: Ben Widawsky <ben@bwidawsk.net>
> > Bugzilla: https://bugs.freedesktop.org/attachment.cgi?id=84818
> > Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
> 
> Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>

Merged, but I've dropped the paragraph about the igt tests again - I just
can't hit the bug any more :( Also I've fixed the bugzilla link, it
pointed at an attachment instead of the bug.
-Daniel

> 
> > ---
> >  drivers/gpu/drm/i915/i915_gem.c | 8 +++++---
> >  1 file changed, 5 insertions(+), 3 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
> > index d9eee14..d12dfc3 100644
> > --- a/drivers/gpu/drm/i915/i915_gem.c
> > +++ b/drivers/gpu/drm/i915/i915_gem.c
> > @@ -2624,8 +2624,11 @@ int i915_vma_unbind(struct i915_vma *vma)
> >  	if (list_empty(&vma->vma_link))
> >  		return 0;
> >  
> > -	if (!drm_mm_node_allocated(&vma->node))
> > -		goto destroy;
> > +	if (!drm_mm_node_allocated(&vma->node)) {
> > +		i915_gem_vma_destroy(vma);
> > +
> 
> I'm equivocal on this particular whitespace. For such short branches, it
> looks neater with a tight return.
> 
> > +		return 0;
> > +	}
> 
> -- 
> Chris Wilson, Intel Open Source Technology Centre

-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch