Hi Martin,
Am Mittwoch, den 20.05.2020, 12:10 +0200 schrieb Martin Fuzzey:
> When using mmap() on a prime imported buffer allocated by a
> different driver (such as imx-drm) the later munmap() does
> not correctly decrement the refcount of the original enaviv_gem_object,
> leading to a leak.
>
> Signed-off-by: Martin Fuzzey <martin.fuzzey@flowbird.group>
> Cc: sta...@vger.kernel.org
What's the use-case where you did hit this issue? mmap'ing of imported
buffers through the etnaviv DRM device is currently not well defined
and I was pondering the idea of forbidding it completely by not
returning a mmap offset for those objects.
Regards,
Lucas
> ---
> drivers/gpu/drm/etnaviv/etnaviv_gem_prime.c | 20 +++++++++++++++++++-
> 1 file changed, 19 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/etnaviv/etnaviv_gem_prime.c
> b/drivers/gpu/drm/etnaviv/etnaviv_gem_prime.c
> index f24dd21..28a01b8 100644
> --- a/drivers/gpu/drm/etnaviv/etnaviv_gem_prime.c
> +++ b/drivers/gpu/drm/etnaviv/etnaviv_gem_prime.c
> @@ -93,7 +93,25 @@ static void *etnaviv_gem_prime_vmap_impl(struct
> etnaviv_gem_object *etnaviv_obj)
> static int etnaviv_gem_prime_mmap_obj(struct etnaviv_gem_object *etnaviv_obj,
> struct vm_area_struct *vma)
> {
> - return dma_buf_mmap(etnaviv_obj->base.dma_buf, vma, 0);
> + int ret;
> +
> + ret = dma_buf_mmap(etnaviv_obj->base.dma_buf, vma, 0);
> +
> + /* drm_gem_mmap_obj() has already been called before this function
> + * and has incremented our refcount, expecting it to be decremented
> + * on unmap() via drm_gem_vm_close().
> + * However dma_buf_mmap() invokes drm_gem_cma_prime_mmap()
> + * that ends up updating the vma->vma_private_data to point to the
> + * dma_buf's gem object.
> + * Hence our gem object here will not have its refcount decremented
> + * when userspace does unmap().
> + * So decrement the refcount here to avoid a memory leak if the dma
> + * buf mapping was successful.
> + */
> + if (!ret)
> + drm_gem_object_put_unlocked(&etnaviv_obj->base);
> +
> + return ret;
> }
>
> static const struct etnaviv_gem_ops etnaviv_gem_prime_ops = {
