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From: Tejun Heo <tj@kernel.org>
To: Ziyang Men <ziyang.meme@gmail.com>
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: Wed, 19 Aug 2026 10:55:59 -1000	[thread overview]
Message-ID: <aoYYX60TCD6cd601@slm.duckdns.org> (raw)
In-Reply-To: <aoTx1eaNNJ+xrUq1@devvm16600.scu0.facebook.com>

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.

Thanks.

-- 
tejun

  reply	other threads:[~2026-08-19 20:56 UTC|newest]

Thread overview: 10+ 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
2026-08-19 20:55           ` Tejun Heo [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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