From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-5.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id DF560C4332F for ; Wed, 22 Sep 2021 06:32:13 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id C75DC61184 for ; Wed, 22 Sep 2021 06:32:13 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232832AbhIVGdl (ORCPT ); Wed, 22 Sep 2021 02:33:41 -0400 Received: from Galois.linutronix.de ([193.142.43.55]:53416 "EHLO galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232710AbhIVGdk (ORCPT ); Wed, 22 Sep 2021 02:33:40 -0400 Date: Wed, 22 Sep 2021 08:32:08 +0200 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1632292329; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=LHGvGMeI0MChbmKlKUQjDfvhqjuQaXlro5jHJuiZF4w=; b=AFVjxbaCU1HStARR3s5GptNPD2J5/N0DhTmeIwza4KWjgE+XUqWjrBrxHbQGi7hd7Zc7js BHFE42pswXTDMhQasgTwaXzYu1Z5U7vQqOUkhQxJkwL44gOvnvS936y1q6EXfoP6eSvqAj Zm5RWUWQjozxlGg1uiJx4q+3169rv57mrbiYxUk/p882wbSwK6BZFw6qvBGh3REOZ+X1XY /SBVb/7v658z3MqITZma+6RAWuLc8OqTz8T9jLfSEy2wlmX5hWZmrIpyBGhvNr5mDfW2wD JkAea82CIUY8rNHK5VEh5oHqy1BhWnhx1QTf4WpFKkSKUgGysTJnwsKbugSQ3g== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1632292329; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=LHGvGMeI0MChbmKlKUQjDfvhqjuQaXlro5jHJuiZF4w=; b=XOSDGiTQMoMm+wYlF4/FhKR/TW81atLKv4UkTrp7RxxMkfUED2spl7KHV32imSzOmG+EnO gY3q8TF3EL5ks0CA== From: Sebastian Andrzej Siewior To: Frederic Weisbecker Cc: Thomas Gleixner , Valentin Schneider , linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, rcu@vger.kernel.org, linux-rt-users@vger.kernel.org, Catalin Marinas , Will Deacon , Ingo Molnar , Peter Zijlstra , Steven Rostedt , Daniel Bristot de Oliveira , "Paul E. McKenney" , Josh Triplett , Mathieu Desnoyers , Davidlohr Bueso , Lai Jiangshan , Joel Fernandes , Anshuman Khandual , Vincenzo Frascino , Steven Price , Ard Biesheuvel , Boqun Feng , Mike Galbraith Subject: Re: rcu/tree: Protect rcu_rdp_is_offloaded() invocations on RT Message-ID: <20210922063208.ltf7sdou4tr5yrnc@linutronix.de> References: <20210811201354.1976839-1-valentin.schneider@arm.com> <20210811201354.1976839-4-valentin.schneider@arm.com> <874kae6n3g.ffs@tglx> <87pmt163al.ffs@tglx> <20210921234518.GB100318@lothringen> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20210921234518.GB100318@lothringen> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2021-09-22 01:45:18 [+0200], Frederic Weisbecker wrote: > > Also while at it, I'm asking again: traditionally softirqs could assume that > manipulating a local state was safe against !irq_count() code fiddling with > the same state on the same CPU. > > Now with preemptible softirqs, that assumption can be broken anytime. RCU was > fortunate enough to have a warning for that. But who knows how many issues like > this are lurking? If "local state" is modified then it is safe as long as it is modified within a local_bh_disable() section. And we are in this section while invoking a forced-threaded interrupt. The special part about RCU is that it is used in_irq() as part of core-code. > Thanks. Sebastian