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=-5.9 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,NICE_REPLY_A, 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 107C9C433E7 for ; Fri, 28 Aug 2020 16:01:46 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id E3ACD208D5 for ; Fri, 28 Aug 2020 16:01:45 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1598630505; bh=C9e4JWgOXMyAeZGFAs1HgB2Jk5Sbc+z66fHTKpOP0Cs=; h=Date:From:To:Cc:Subject:In-Reply-To:References:List-ID:From; b=Cq5HImueLlZfWGXRQ7UGbXtVR9x1/fzjQkvXa2ITpk8zVS1JWJ7sS2oyKGFig5D3l IGihHIVa4a7FibbHOE8L5XgN+ElixHlqQloYjQCwAwgtukaHjz1s/Z8JvYagIjpbFW 0GxRECujFr38/jUYC8GjbUsOj6dn/P/wdGA75q14= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728511AbgH1QBo (ORCPT ); Fri, 28 Aug 2020 12:01:44 -0400 Received: from mail.kernel.org ([198.145.29.99]:52942 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728453AbgH1QBj (ORCPT ); Fri, 28 Aug 2020 12:01:39 -0400 Received: from devnote2 (NE2965lan1.rev.em-net.ne.jp [210.141.244.193]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id DCA5D2075B; Fri, 28 Aug 2020 16:01:36 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1598630499; bh=C9e4JWgOXMyAeZGFAs1HgB2Jk5Sbc+z66fHTKpOP0Cs=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=dBdPRoj3USsELHAeAEg/pq9jx0Z3hh0xUKTeq2hX56d+ZMGsMWPS4ScVwTlpLuuNA WGAxIq2dPTIVaV4jb88sMajN5bMoFeobnviXcuKaPU8Hza03Qdwy11tEHzAiKmu92b TWlTno0Bevb0SuOZrjIUaoNFq/2eRkptT1PaX7hc= Date: Sat, 29 Aug 2020 01:01:35 +0900 From: Masami Hiramatsu To: peterz@infradead.org Cc: linux-kernel@vger.kernel.org, Eddy_Wu@trendmicro.com, x86@kernel.org, davem@davemloft.net, rostedt@goodmis.org, naveen.n.rao@linux.ibm.com, anil.s.keshavamurthy@intel.com, linux-arch@vger.kernel.org, cameron@moodycamel.com, oleg@redhat.com, will@kernel.org, paulmck@kernel.org Subject: Re: [PATCH v4 20/23] [RFC] kprobes: Remove task scan for updating kretprobe_instance Message-Id: <20200829010135.faf4657147aed64beb896a08@kernel.org> In-Reply-To: <20200828151806.GF1362448@hirez.programming.kicks-ass.net> References: <159861759775.992023.12553306821235086809.stgit@devnote2> <159861781740.992023.4956784710984854658.stgit@devnote2> <20200828125236.GA1362448@hirez.programming.kicks-ass.net> <20200829001010.7ec1a183c2294f7bd843b153@kernel.org> <20200828151806.GF1362448@hirez.programming.kicks-ass.net> X-Mailer: Sylpheed 3.7.0 (GTK+ 2.24.32; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 28 Aug 2020 17:18:06 +0200 peterz@infradead.org wrote: > On Sat, Aug 29, 2020 at 12:10:10AM +0900, Masami Hiramatsu wrote: > > On Fri, 28 Aug 2020 14:52:36 +0200 > > peterz@infradead.org wrote: > > > > > synchronize_rcu(); > > > > > > This one might help, this means we can do rcu_read_lock() around > > > get_kretprobe() and it's usage. Can we call rp->handler() under RCU? > > > > Yes, as I said above, the get_kretprobe() (and kretprobe handler) must be > > called under preempt-disabled. > > Then we don't need the ordering; we'll need READ_ONCE() (or > rcu_derefernce()) to make sure the address dependency works on Alpha. > And a comment/assertion that explains this might not go amiss in > get_kretprobe(). OK, I'll rewrite it with READ_ONCE() and rcu_read_lock_any_held(). Thank you, -- Masami Hiramatsu