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Thu, 20 Aug 2026 13:05:04 -0700 (PDT) Date: Thu, 20 Aug 2026 13:05:01 -0700 From: Ziyang Men To: Tejun Heo Cc: Johannes Weiner , Michal =?iso-8859-1?Q?Koutn=FD?= , Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , Eduard Zingerman , Kumar Kartikeya Dwivedi , Shuah Khan , kernel-team@meta.com, Ingo Molnar , Peter Zijlstra , Vincent Guittot , Ben Segall , Dietmar Eggemann , Martin KaFai Lau , Song Liu , Yonghong Song , Jiri Olsa , Emil Tsalapatis , Roman Gushchin , Shakeel Butt , JP Kobryn , 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 Message-ID: References: <20260818002450.3071325-1-ziyang.meme@gmail.com> <20260818002450.3071325-2-ziyang.meme@gmail.com> Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Disposition: inline In-Reply-To: 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