Re: [PATCH v2 1/2] block: add BPF kfuncs to read blkcg io.stat

Hi Tejun,

On Wed, Aug 19, 2026 at 12:51:57PM -1000, Tejun Heo wrote:
>Hello,
>
>On Wed, Aug 19, 2026 at 03:20:17PM -0700, Ziyang Men wrote:
>> Yes the css_rstat_flush() is exposed but currently it is marked as SLEEPABLE, so
>> it doesn't accept a RCU_PROTECTED css we proposed. This is not a problem for cpu
>> ones since &cgrp->self is a trusted pointer.
>
>Yeah, bummer, so we get ref on cgroups but the subsys pointers are RCU, so
>that means those refs are only RCU protected. I guess we can't avoid a kfunc
>to get acquire a subsys css from cgroup. I wish css_rstat_flush() didn't
>schedule but it does need that cond_resched().

Yeah that would be a pity. I will add kfuncs bpf_cgroup_css() and
bpf_css_release() to handle the reference for the css.

The bpf_blkcg_flush_stats() will be removed as well.

Thanks,
Ziyang

>
>Thanks.
>
>-- 
>tejun