On 29/11/2019 13:59, Boris Brezillon wrote:
> panfrost_gem_shrinker_scan() might purge a BO (release the sgt and
> kill the GPU mapping) that's being freed by panfrost_gem_free_object()
> if we don't remove the BO from the shrinker list at the beginning of
> panfrost_gem_free_object().
>
> Fixes: 013b65101315 ("drm/panfrost: Add madvise and shrinker support")
> Cc: <sta...@vger.kernel.org>
> Signed-off-by: Boris Brezillon <boris.brezil...@collabora.com>
Reviewed-by: Steven Price <steven.pr...@arm.com>
> ---
> drivers/gpu/drm/panfrost/panfrost_gem.c | 15 ++++++++++-----
> 1 file changed, 10 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/gpu/drm/panfrost/panfrost_gem.c
> b/drivers/gpu/drm/panfrost/panfrost_gem.c
> index acb07fe06580..daf4c55a2863 100644
> --- a/drivers/gpu/drm/panfrost/panfrost_gem.c
> +++ b/drivers/gpu/drm/panfrost/panfrost_gem.c
> @@ -19,6 +19,16 @@ static void panfrost_gem_free_object(struct drm_gem_object
> *obj)
> struct panfrost_gem_object *bo = to_panfrost_bo(obj);
> struct panfrost_device *pfdev = obj->dev->dev_private;
>
> + /*
> + * Make sure the BO is no longer inserted in the shrinker list before
> + * taking care of the destruction itself. If we don't do that we have a
> + * race condition between this function and what's done in
> + * panfrost_gem_shrinker_scan().
> + */
> + mutex_lock(&pfdev->shrinker_lock);
> + list_del_init(&bo->base.madv_list);
> + mutex_unlock(&pfdev->shrinker_lock);
> +
> if (bo->sgts) {
> int i;
> int n_sgt = bo->base.base.size / SZ_2M;
> @@ -33,11 +43,6 @@ static void panfrost_gem_free_object(struct drm_gem_object
> *obj)
> kfree(bo->sgts);
> }
>
> - mutex_lock(&pfdev->shrinker_lock);
> - if (!list_empty(&bo->base.madv_list))
> - list_del(&bo->base.madv_list);
> - mutex_unlock(&pfdev->shrinker_lock);
> -
> drm_gem_shmem_free_object(obj);
> }
>
>
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