From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 4F2AE32A3FE; Wed, 19 Aug 2026 20:56:00 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787172961; cv=none; b=VEWht/NHDOqLDQ4Dv2UDrExOeP5TPvJxtaxkdfcq/UWJkncCRa+DSNkPvH9T8XyutXwxbijLAJQqpthx9OQMu9oG1vnU1c26Ee4y9AECbBjETK3+JibdLp7Mj/ze4kjYYzUL5DKWyARWAHslJ+pdgjLybOreeE1vV9XCKBRVdA0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787172961; c=relaxed/simple; bh=3fMlJ5q4zJl8LSi+24VIiJMReeJUbFu+/qPmIwhhfZY=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=ezIyjB09s4ThRbl1KV7umWPvq4ximhSRC96UXUIP4WJmtGzTg7w/lW66Ivs4zJRicK009RXX/RJfssNuvP0LztySRI3cFQY/OlT68928YxrYUWr4H2qaCdxdmG5VZJlBB8OPYWyLgF+6bQsnvioaB1uK/lirOiQ/Qj5SkIfRwR0= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=WsqfidD1; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="WsqfidD1" Received: by smtp.kernel.org (Postfix) with ESMTPSA id BDCF01F000E9; Wed, 19 Aug 2026 20:55:59 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1787172959; bh=VeFgLXE0eOoS7AHpMF3PhMjzRNqkuytehVXLwAv1H7M=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=WsqfidD12kj8bghrIGixK9B+HlQujU9bxPPYkzi8ejdZ3OroUueKiyhya4LuzyL90 IF3lujhfR8qL4zqTmSy3td+xzNRQO+DMKGOlPmAqP0gXXP0V7gPsv/uG1lrDMMGfJb TwzKQaXcqNQincreKdL0Bq5ECcUIVTpgak/5p2PkEAklBHsGaVbF7MpZvq1bc5nqzO taYY1PNe/e5/Dto/QMBw2CkQtCrDGyCMlkbvPeUA5uxtMmcUCOlcyScsDeLYLi9SRV ZVRpWuY37efAaXlSaQFhqsOZwgu25Au33e7IpQ1blcTnDHGrW4xd4sh6WgYgU9/NG7 DVZcOQ4aJHPbg== Date: Wed, 19 Aug 2026 10:55:59 -1000 From: Tejun Heo To: Ziyang Men 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: cgroups@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: 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