Re: [PATCH 6/8] drm/panfrost: Make sure imported/exported BOs are never purged

[Boris Brezillon <boris.brezillon@collabora.com>]

On Fri, 29 Nov 2019 14:45:41 +0000
Steven Price <steven.price@arm.com> wrote:

> On 29/11/2019 13:59, Boris Brezillon wrote:
> > We don't want imported/exported BOs to be purges, as those are shared  
> 
> s/purges/purged/
> 
> > with other processes that might still use them. We should also refuse
> > to export a BO if it's been marked purgeable or has already been purged.
> > 
> > Fixes: 013b65101315 ("drm/panfrost: Add madvise and shrinker support")
> > Cc: <stable@vger.kernel.org>
> > Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com>
> > ---
> >  drivers/gpu/drm/panfrost/panfrost_drv.c | 19 ++++++++++++++++-
> >  drivers/gpu/drm/panfrost/panfrost_gem.c | 27 +++++++++++++++++++++++++
> >  2 files changed, 45 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/gpu/drm/panfrost/panfrost_drv.c b/drivers/gpu/drm/panfrost/panfrost_drv.c
> > index 1c67ac434e10..751df975534f 100644
> > --- a/drivers/gpu/drm/panfrost/panfrost_drv.c
> > +++ b/drivers/gpu/drm/panfrost/panfrost_drv.c
> > @@ -343,6 +343,7 @@ static int panfrost_ioctl_madvise(struct drm_device *dev, void *data,
> >  	struct drm_panfrost_madvise *args = data;
> >  	struct panfrost_device *pfdev = dev->dev_private;
> >  	struct drm_gem_object *gem_obj;
> > +	int ret;
> >  
> >  	gem_obj = drm_gem_object_lookup(file_priv, args->handle);
> >  	if (!gem_obj) {
> > @@ -350,6 +351,19 @@ static int panfrost_ioctl_madvise(struct drm_device *dev, void *data,
> >  		return -ENOENT;
> >  	}
> >  
> > +	/*
> > +	 * We don't want to mark exported/imported BOs as purgeable: we're not
> > +	 * the only owner in that case.
> > +	 */
> > +	mutex_lock(&dev->object_name_lock);
> > +	if (gem_obj->dma_buf)
> > +		ret = -EINVAL;
> > +	else
> > +		ret = 0;
> > +
> > +	if (ret)
> > +		goto out_unlock_object_name;
> > +  
> 
> This might be better by setting ret = 0 at the beginning of the
> function. This can then be re-written as the more normal:
> 
> 	if (gem_obj->dma_buf) {
> 		ret = -EINVAL;
> 		goto out_unlock_object_name;
> 	]

Agreed.

> 
> >  	mutex_lock(&pfdev->shrinker_lock);
> >  	args->retained = drm_gem_shmem_madvise(gem_obj, args->madv);
> >  
> > @@ -364,8 +378,11 @@ static int panfrost_ioctl_madvise(struct drm_device *dev, void *data,
> >  	}
> >  	mutex_unlock(&pfdev->shrinker_lock);
> >  
> > +out_unlock_object_name:
> > +	mutex_unlock(&dev->object_name_lock);
> > +
> >  	drm_gem_object_put_unlocked(gem_obj);
> > -	return 0;
> > +	return ret;
> >  }
> >  
> >  int panfrost_unstable_ioctl_check(void)
> > diff --git a/drivers/gpu/drm/panfrost/panfrost_gem.c b/drivers/gpu/drm/panfrost/panfrost_gem.c
> > index 92a95210a899..31d6417dd21c 100644
> > --- a/drivers/gpu/drm/panfrost/panfrost_gem.c
> > +++ b/drivers/gpu/drm/panfrost/panfrost_gem.c
> > @@ -99,6 +99,32 @@ void panfrost_gem_close(struct drm_gem_object *obj, struct drm_file *file_priv)
> >  	spin_unlock(&priv->mm_lock);
> >  }
> >  
> > +static struct dma_buf *
> > +panfrost_gem_export(struct drm_gem_object *obj, int flags)
> > +{
> > +	struct panfrost_gem_object *bo = to_panfrost_bo(obj);
> > +	int ret;
> > +
> > +	/*
> > +	 * We must make sure the BO has not been marked purgeable/purged before
> > +	 * adding the mapping.
> > +	 * Note that we don't need to protect this test with a lock because
> > +	 * &drm_gem_object_funcs.export() is called with
> > +	 * &drm_device.object_lock held, and panfrost_ioctl_madvise() takes
> > +	 * this lock before calling drm_gem_shmem_madvise() (the function that
> > +	 * modifies bo->base.madv).
> > +	 */
> > +	if (bo->base.madv == PANFROST_MADV_WILLNEED)
> > +		ret = -EINVAL;
> > +	else
> > +		ret = 0;
> > +
> > +	if (ret)
> > +		return ERR_PTR(ret);  
> 
> No need for ret here:
> 
> 	if (bo->base.madv == PANFROST_MADV_WILLNEED)
> 		return ERR_PTR(-EINVAL);

This if/else section was previously surrounded by a lock/unlock, hence
the convoluted logic. I'll rework as suggested.

Thanks.