Re: [PATCH-block v2 1/3] bdi, blk-cgroup: Fix potential UAF of blkcg

[Tejun Heo]

On Sun, Dec 11, 2022 at 05:20:56PM -0500, Waiman Long wrote:
>  static void blkcg_destroy_blkgs(struct blkcg *blkcg)
>  {
> +	/*
> +	 * blkcg_destroy_blkgs() shouldn't be called with all the blkcg
> +	 * references gone.
> +	 */
> +	if (WARN_ON_ONCE(!css_tryget(&blkcg->css)))
> +		return;

Wouldn't it make more sense to use percpu_ref_is_zero()? It's not like the
obtained extra reference does anything, right?

Thanks.

-- 
tejun