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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 4ED0FC25B67 for ; Fri, 27 Oct 2023 11:49:52 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1345784AbjJ0Ltw (ORCPT ); Fri, 27 Oct 2023 07:49:52 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:59780 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1345734AbjJ0Ltt (ORCPT ); Fri, 27 Oct 2023 07:49:49 -0400 Received: from out203-205-251-53.mail.qq.com (out203-205-251-53.mail.qq.com [203.205.251.53]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 621E0C1 for ; Fri, 27 Oct 2023 04:49:47 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=foxmail.com; s=s201512; t=1698407385; bh=vovYC7XL/z97oRsMWqemvOzOIpZfGfmSdXKAPD1GtMc=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=qBSPu9hNCFNoAxjCLazNHpTbcCrb8ksYefrLio37TMHORlDBhlGFXNY5LcNrpNBWA VkKSH5nSvd+RMNItV7tk8VEjLjIVKM26yPP9NaG4XG5GAwF7H4oyljpkYtCi+w5/Hd ppY+q9XXSiY6dijo4hQGUBwdUjtn6R/aEHyekizk= Received: from [10.56.52.5] ([39.156.73.12]) by newxmesmtplogicsvrszc2-0.qq.com (NewEsmtp) with SMTP id C6B2E448; Fri, 27 Oct 2023 19:49:43 +0800 X-QQ-mid: xmsmtpt1698407383tcu8w1450 Message-ID: X-QQ-XMAILINFO: NhUkPfKlCtQwyapd5mDfNjVG3GVyBw/QJahB3RDGob+3+rhq6i/POFBG+8tzhM jG9tqAHnDeFMADQy5WqG1qatWPfa4JtQubM8j+fywthnx8s8Oo4H0RxOHWmYL7BvMKUCU1sEGyl6 8fniJenjtSeInxCobv9u2h9jK8m/hUKKzLqpmmRvh3BbyvTPQBAiVHyMx8Rpt0XiaCLHMHaVMLyw 87sC+hvWlUgqcSYgiToHT9w3BuFuV5GJQ9rXle9zdiIX73FKSfcnpqJgjIOCKjWP6Wp6xByQgCfU Zpl3FYpFYRZP5I8j4aJ8fQMi6RSvnz3zernuqn4o7E2+HWP05QREZp3qrnWqJzQEIVNTWK//xmKn YQt51GJd4mtHlMqT9TrGiQqtgyqq8OyRvYrEXeTTq8DSa7ODMGbTkcv0GMsETKS3C2h8LcVeSBqb EwM4iAxnX6VwBPbPMFxp+il7CquVqNm9t0DWjzMN02ne2ElK4umq7d1wGB/1EABOpiQ+XO1CbySu qJldcL/QMn1Zc5QEnxHuj74f07a0n6GQ0zVF7W4L0yXsXVOBUGsKCpxA8yVWWKYQwwrJ6mdupzHC DzebYZjdyG0LHCK9t6GMK9pZnJBxObBaEZjDYrnSdIv0nHJ8neA/n43n3WpxO82H/EuigJH/7S56 VKsSmO/5hNvSk+9q2bGhjAW1rImp8glsjmnsT/2tP1UIxecwgjgN3Nw1y2LCkUpNhNmXbBwybSjS ubg+vDDg+5TFubrCKgdK3Pvc2M61G+lvfr/wyRGvnk105H4UvL6FM0jK7ppSaZ/gPQrS1qHczHnT 7Zs0FlojoO565Hp90KwtRj6O4v0jkjCEdPLmzD8lzzUalSDJZ5agrbs1qvVURh+jpFmO77cHHWoj Xw+PglSoKbeudtfCHXjaa0EJxFJsKb3TJMZBcX4s01GZ5hcoXbOJVsto5I+iSbq5KDNUZHsZZ+l/ nnH4XAp+xWL1iuSsFj6yNaQ/QECpRlktqE1tTxFBCE1/4WS5vWqJCZ+hKvmqCZ X-QQ-XMRINFO: Nq+8W0+stu50PRdwbJxPCL0= X-OQ-MSGID: Date: Fri, 27 Oct 2023 19:49:43 +0800 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 1/2] stop_machine: Use non-atomic read multi_stop_data::state clearly Content-Language: en-US To: Mark Rutland Cc: elver@google.com, linux-kernel@vger.kernel.org, peterz@infradead.org, rongtao@cestc.cn, tglx@linutronix.de References: From: Rong Tao In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 10/24/23 6:46 PM, Mark Rutland wrote: > On Fri, Oct 20, 2023 at 10:43:33PM +0800, Rong Tao wrote: >> From: Rong Tao >> >> commit b1fc58333575 ("stop_machine: Avoid potential race behaviour") >> solved the race behaviour problem, to better show that race behaviour >> does not exist, pass the 'curstate' directly to ack_state() instead of >> refetching msdata->state in ack_state(). >> > I'd prefer if we make this: > > | stop_machine: pass curstate to ack_state() > | > | The multi_cpu_stop() state machine uses multi_stop_data::state to hold > | the current state, and this is read and written atomically except in > | ack_state(), which performs a non-atomic read. > | > | As ack_state() only performs this non-atomic read when there is a single > | writer, this is benign, but it makes reasoning about the state machine a > | little harder. > | > | Remove the non-atomic read and pass the (atomically read) curstate in > | instead. This makes it clear that we do not expect any racy writes, and > | avoids a redundant load. > > With that wording: > > Acked-by: Mark Rutland > > Mark. Hi, Mark, I just submit a single patch [0] individually, not as a patchset. please review. thank you. Rong Tao [0] https://lore.kernel.org/lkml/tencent_FB1D31CEC045E837ABE5B25CC5E37575F405@qq.com/ > >> Signed-off-by: Rong Tao >> --- >> kernel/stop_machine.c | 7 ++++--- >> 1 file changed, 4 insertions(+), 3 deletions(-) >> >> diff --git a/kernel/stop_machine.c b/kernel/stop_machine.c >> index cedb17ba158a..268c2e581698 100644 >> --- a/kernel/stop_machine.c >> +++ b/kernel/stop_machine.c >> @@ -188,10 +188,11 @@ static void set_state(struct multi_stop_data *msdata, >> } >> >> /* Last one to ack a state moves to the next state. */ >> -static void ack_state(struct multi_stop_data *msdata) >> +static void ack_state(struct multi_stop_data *msdata, >> + enum multi_stop_state curstate) >> { >> if (atomic_dec_and_test(&msdata->thread_ack)) >> - set_state(msdata, msdata->state + 1); >> + set_state(msdata, curstate + 1); >> } >> >> notrace void __weak stop_machine_yield(const struct cpumask *cpumask) >> @@ -242,7 +243,7 @@ static int multi_cpu_stop(void *data) >> default: >> break; >> } >> - ack_state(msdata); >> + ack_state(msdata, curstate); >> } else if (curstate > MULTI_STOP_PREPARE) { >> /* >> * At this stage all other CPUs we depend on must spin >> -- >> 2.41.0 >>