Re: [PATCH v2 1/2] cgroup: add BPF kfuncs to read a cpu cgroup's stats

Hi Tejun,

On Wed, Aug 19, 2026 at 10:55:59AM -1000, Tejun Heo wrote:
>Hello,
>
>On Tue, Aug 18, 2026 at 04:59:17PM -0700, Ziyang Men wrote:
>> > > The bpf_cgroup_base_stat() takes an rstat spinlock_t, which can sleep on
>> > > PREEMPT_RT.
>> >
>> > Is this actually required? This doesn't really make sense to me. Shouldn't
>> > what SLEEPABLE mean change on RT kernels instead?
>>
>> Oh sorry, I didn't notice that.
>>
>> I might be wrong: this function calls the cputime_adjust(), which in turn
>> acquires raw_spin_lock_irqsave(), so there would be NMI deadlock in the
>> perf_event program. The __css_rstat_lock() take the spin_lock_irq() as well. So
>> maybe a SLEEPABLE tag is still necessary?
>
>I think this is for BPF folks to answer. I don't think SLEEPABLE is needed
>because of RT but yeah it wouldn't be safe to be called from nmi context.

Ok I see, let's remove the SLEEPABLE for now. 

Thanks,
Ziyang

>
>Thanks.
>
>-- 
>tejun