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

[Waiman Long <longman@xxxxxxxxxx>]

On 12/12/22 17:13, Tejun Heo wrote:
> 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?

Yes, that makes sense. Will incorporate the change in the next version.

Thanks,
Longman