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

[Tejun Heo]

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().

Thanks.

-- 
tejun