[PATCH] drm/ttm: Warn on pinning without holding a reference

[Daniel Vetter]

On Wed, Oct 28, 2020 at 01:11:51PM +0100, Christian König wrote:
> Am 28.10.20 um 12:31 schrieb Daniel Vetter:
> > Not technically a problem for ttm, but very likely a driver bug and
> > pretty big time confusing for reviewing code.
> > 
> > So warn about it, both at cleanup time (so we catch these for sure)
> > and at pin/unpin time (so we know who's the culprit).
> > 
> > Signed-off-by: Daniel Vetter <daniel.vetter at intel.com>
> > Cc: Christian Koenig <christian.koenig at amd.com>
> > Cc: Huang Rui <ray.huang at amd.com>
> 
> Reviewed-by: Christian König <christian.koenig at amd.com>

Remembered this patch, pushed it. Thanks to you both for the reviews.
-Daniel

> 
> > ---
> >   drivers/gpu/drm/ttm/ttm_bo.c | 2 +-
> >   include/drm/ttm/ttm_bo_api.h | 2 ++
> >   2 files changed, 3 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/gpu/drm/ttm/ttm_bo.c b/drivers/gpu/drm/ttm/ttm_bo.c
> > index f51b5e20fa17..a011072ab61d 100644
> > --- a/drivers/gpu/drm/ttm/ttm_bo.c
> > +++ b/drivers/gpu/drm/ttm/ttm_bo.c
> > @@ -509,7 +509,7 @@ static void ttm_bo_release(struct kref *kref)
> >   		 * shrinkers, now that they are queued for
> >   		 * destruction.
> >   		 */
> > -		if (bo->pin_count) {
> > +		if (WARN_ON(bo->pin_count)) {
> >   			bo->pin_count = 0;
> >   			ttm_bo_del_from_lru(bo);
> >   			ttm_bo_add_mem_to_lru(bo, &bo->mem);
> > diff --git a/include/drm/ttm/ttm_bo_api.h b/include/drm/ttm/ttm_bo_api.h
> > index 37102e45e496..b45aee23d7d0 100644
> > --- a/include/drm/ttm/ttm_bo_api.h
> > +++ b/include/drm/ttm/ttm_bo_api.h
> > @@ -571,6 +571,7 @@ static inline bool ttm_bo_uses_embedded_gem_object(struct ttm_buffer_object *bo)
> >   static inline void ttm_bo_pin(struct ttm_buffer_object *bo)
> >   {
> >   	dma_resv_assert_held(bo->base.resv);
> > +	WARN_ON_ONCE(!kref_read(&bo->kref));
> >   	++bo->pin_count;
> >   }
> > @@ -584,6 +585,7 @@ static inline void ttm_bo_unpin(struct ttm_buffer_object *bo)
> >   {
> >   	dma_resv_assert_held(bo->base.resv);
> >   	WARN_ON_ONCE(!bo->pin_count);
> > +	WARN_ON_ONCE(!kref_read(&bo->kref));
> >   	--bo->pin_count;
> >   }
> 

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