From: Ziyang Men <ziyang.meme@gmail.com>
To: Tejun Heo <tj@kernel.org>
Cc: "Johannes Weiner" <hannes@cmpxchg.org>,
"Michal Koutný" <mkoutny@suse.com>,
"Alexei Starovoitov" <ast@kernel.org>,
"Daniel Borkmann" <daniel@iogearbox.net>,
"Andrii Nakryiko" <andrii@kernel.org>,
"Eduard Zingerman" <eddyz87@gmail.com>,
"Kumar Kartikeya Dwivedi" <memxor@gmail.com>,
"Shuah Khan" <shuah@kernel.org>,
kernel-team@meta.com, "Ingo Molnar" <mingo@redhat.com>,
"Peter Zijlstra" <peterz@infradead.org>,
"Vincent Guittot" <vincent.guittot@linaro.org>,
"Ben Segall" <bsegall@google.com>,
"Dietmar Eggemann" <dietmar.eggemann@arm.com>,
"Martin KaFai Lau" <martin.lau@linux.dev>,
"Song Liu" <song@kernel.org>,
"Yonghong Song" <yonghong.song@linux.dev>,
"Jiri Olsa" <jolsa@kernel.org>,
"Emil Tsalapatis" <emil@etsalapatis.com>,
"Roman Gushchin" <roman.gushchin@linux.dev>,
"Shakeel Butt" <shakeel.butt@linux.dev>,
"JP Kobryn" <inwardvessel@gmail.com>,
bpf@vger.kernel.org, cgroups@vger.kernel.org,
linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2 1/2] cgroup: add BPF kfuncs to read a cpu cgroup's stats
Date: Tue, 18 Aug 2026 16:59:17 -0700 [thread overview]
Message-ID: <aoTx1eaNNJ+xrUq1@devvm16600.scu0.facebook.com> (raw)
In-Reply-To: <aoTg7ybddqzoZbz7@slm.duckdns.org>
Hi Tejun,
On Tue, Aug 18, 2026 at 12:47:11PM -1000, Tejun Heo wrote:
>On Tue, Aug 18, 2026 at 03:44:36PM -0700, Ziyang Men wrote:
>> > > +BTF_KFUNCS_START(bpf_rstat_common_kfunc_ids)
>> > > +BTF_ID_FLAGS(func, bpf_css_flush_rstat, KF_SLEEPABLE)
>> > > +BTF_ID_FLAGS(func, bpf_cgroup_base_stat, KF_SLEEPABLE)
>> >
>> > Why are these SLEEPABLE?
>> >
>>
>> The css_rstat_flush() calls might_sleep() and cond_resched().
>
>I see.
>
>> 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?
Please let me know your concerns. Thanks!
Best,
Ziyang
>
>Thanks.
>
>--
>tejun
next prev parent reply other threads:[~2026-08-18 23:59 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-08-18 0:24 [PATCH v2 0/2] cgroup: expose cpu.stat to BPF Ziyang Men
2026-08-18 0:24 ` [PATCH v2 1/2] cgroup: add BPF kfuncs to read a cpu cgroup's stats Ziyang Men
2026-08-18 1:28 ` bot+bpf-ci
2026-08-18 17:16 ` Tejun Heo
2026-08-18 22:44 ` Ziyang Men
2026-08-18 22:47 ` Tejun Heo
2026-08-18 23:59 ` Ziyang Men [this message]
2026-08-18 0:24 ` [PATCH v2 2/2] selftests/bpf: add cgroup_iter_cpu test for cpu cgroup kfuncs Ziyang Men
2026-08-18 1:28 ` bot+bpf-ci
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