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

On 8/11/26 9:54 AM, Tejun Heo wrote:
> Hello,
> 
> On Mon, Aug 10, 2026 at 05:17:26PM -0700, JP Kobryn wrote:
> ...
>> The get/put kfuncs above use KF_ACQUIRE/RELEASE so the verifier can
>> reject memcg access after the put. Replacing them with a generic API
>> would call for tracking a new lifetime relationship between the css and
>> memcg (or other derived) pointer.
> 
> So, if you need css -> memcg casting, I think that can just be RCU
> protected. In fact, even for the iteration and access, RCU protection
> probably makes more sense then KF_ACQUIRE/RELEASE. It's simpler and less
> overhead especially given that most bpf progs that people care about are
> non-sleepable and already in RCU critical section anyway.
> 
It's just that if flushing is involved, the cond_resched() within
css_rstat_flush() would preclude RCU.