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

Tejun Heo
2022-12-12T22:13:56Z

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