From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from relay.hostedemail.com (smtprelay0010.hostedemail.com [216.40.44.10]) (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 2ED422F85E9; Thu, 17 Jul 2025 15:12:23 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=216.40.44.10 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1752765146; cv=none; b=SZipgOWIoRK1puLMqhkXcnB1sP5VXWhuzKqoCq+hgbBWILazhiPL8+5PodH3s8yP6CQXv8Amn4kxR0/qnIPVIAhnXP9GpLZy6TOoRYlUMQy+dG34ZU4O0728pI3OevPgo0GtapT4s5tdiSSTHhHcKFWJ381xvdnCyDUCQa+OUbo= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1752765146; c=relaxed/simple; bh=xxGj8cNrd82Pl24JxRI0cygThMCZ/XGFAujXMZmBd7g=; h=Date:From:To:Cc:Subject:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=kJDCC8V+8r1bylZR+jqK04jqdI3uhAQADIZ15ZNR8WIuonyY7mCCofNbue+mtlHGQ477k7mc38Csf5L6Le6dWsk6SdkSot41kKtT4j+9G1DK9L7ejM+izI7kCSbeH2rXcoJVhuWgM95T/duVYe7BqV1WKQrOku7Qmlgnw2YV+yU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=goodmis.org; spf=pass smtp.mailfrom=goodmis.org; arc=none smtp.client-ip=216.40.44.10 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=goodmis.org Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=goodmis.org Received: from omf06.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay01.hostedemail.com (Postfix) with ESMTP id 968151D25F8; Thu, 17 Jul 2025 15:12:21 +0000 (UTC) Received: from [HIDDEN] (Authenticated sender: rostedt@goodmis.org) by omf06.hostedemail.com (Postfix) with ESMTPA id 76DE620013; Thu, 17 Jul 2025 15:12:17 +0000 (UTC) Date: Thu, 17 Jul 2025 11:12:16 -0400 From: Steven Rostedt To: Alexei Starovoitov Cc: Mathieu Desnoyers , "Paul E. McKenney" , Sebastian Andrzej Siewior , Boqun Feng , linux-rt-devel@lists.linux.dev, rcu@vger.kernel.org, linux-trace-kernel , Frederic Weisbecker , Joel Fernandes , Josh Triplett , Lai Jiangshan , Masami Hiramatsu , Neeraj Upadhyay , Thomas Gleixner , Uladzislau Rezki , Zqiang , bpf Subject: Re: [RFC PATCH 1/2] rcu: Add rcu_read_lock_notrace() Message-ID: <20250717111216.4949063d@batman.local.home> In-Reply-To: References: <03083dee-6668-44bb-9299-20eb68fd00b8@paulmck-laptop> <29b5c215-7006-4b27-ae12-c983657465e1@efficios.com> <512331d8-fdb4-4dc1-8d9b-34cc35ba48a5@paulmck-laptop> <16dd7f3c-1c0f-4dfd-bfee-4c07ec844b72@paulmck-laptop> <20250716110922.0dadc4ec@batman.local.home> <895b48bd-d51e-4439-b5e0-0cddcc17a142@paulmck-laptop> X-Mailer: Claws Mail 3.17.8 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Precedence: bulk X-Mailing-List: linux-trace-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: quoted-printable X-Stat-Signature: 5gyaquas5ioppiie5ckjo9ruz5i4zk7g X-Rspamd-Server: rspamout08 X-Rspamd-Queue-Id: 76DE620013 X-Session-Marker: 726F737465647440676F6F646D69732E6F7267 X-Session-ID: U2FsdGVkX1+ffovo8fsNi0fX63qatArRAunOSWznX20= X-HE-Tag: 1752765137-569355 X-HE-Meta: U2FsdGVkX1+b0EYH5NrxOQ+jfOYOt/z5FWFjZ0WbQLRNjwDfJlJjQLAZgOvItOXgTvcorYTgkkiW1rzDahLR77azVN9TQ8M9xtpB5ZxQYN6BI6FLRsPQUXcoPlrd0SProDOxHU2R0ZbsDZxCP4B0+8aLxqXOHyXmF61N2KsANbni4JMM2rXmOq0wH7xp/obxI7ElVvIUqOtnbdkg2PZLXO6FlyGcqGqIIMdvWWPIhnJM1uUb/0tFqqun2qA91arlYoIQ5KipDCeBM6BDxbtdjVeur5eSsH9puJVjewog0U0mjmmadJ56ueo93N5lr2jAMnSViGOcxpb0bBfQMwIkUl80LuaFncAX On Thu, 17 Jul 2025 07:57:27 -0700 Alexei Starovoitov wrote: > I still don't understand what problem is being solved. > As current tracepoint code stands there is no issue with it at all > on PREEMPT_RT from bpf pov. > bpf progs that attach to tracepoints are not sleepable. > They don't call rt_spinlock either. > Recognizing tracepoints that can sleep/fault and allow > sleepable bpf progs there is on our to do list, > but afaik it doesn't need any changes to tracepoint infra. > There is no need to replace existing preempt_disable wrappers > with sleepable srcu_fast or anything else. =46rom the PREEMPT_RT point of view, it wants BPF to be preemptable. It may stop migration, but if someone adds a long running BPF program (when I say long running, it could be anything more than 10us), and it executes on a low priority task. If that BPF program is not preemptable it can delay a high priority task from running. That defeats the purpose of PREEMPT_RT. If this is unsolvable, then we will need to make PREEMPT_RT and BPF mutually exclusive in the configs. -- Steve