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=-5.1 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 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 50BECC433E2 for ; Tue, 15 Sep 2020 18:53:38 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 0957020735 for ; Tue, 15 Sep 2020 18:53:38 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (1024-bit key) header.d=mg.codeaurora.org header.i=@mg.codeaurora.org header.b="bla9us1W" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727586AbgIOSxf (ORCPT ); Tue, 15 Sep 2020 14:53:35 -0400 Received: from m43-7.mailgun.net ([69.72.43.7]:51662 "EHLO m43-7.mailgun.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727821AbgIORYO (ORCPT ); Tue, 15 Sep 2020 13:24:14 -0400 DKIM-Signature: a=rsa-sha256; v=1; c=relaxed/relaxed; d=mg.codeaurora.org; q=dns/txt; s=smtp; t=1600190650; h=Content-Transfer-Encoding: Content-Type: In-Reply-To: MIME-Version: Date: Message-ID: From: References: Cc: To: Subject: Sender; bh=mmUpR8kyg48G1ucp+HFseTlZkNpLrALzY0olaGIaa88=; b=bla9us1WSwTAuU22+WO5ykrSqU5TDYOiw08E5nsLgMcFEGvjdacHjqy6fpQ3V/whL4kxRhvF bdgA+vFNw905fbkgm7mz71fM3Eawt1rtQxUhCUtpBc8rGv1Su046MG1Ymtlt5J+bJhd6CvWl M0/QQB7b8XYl/bFEVACxezFKzB0= X-Mailgun-Sending-Ip: 69.72.43.7 X-Mailgun-Sid: WyI0MWYwYSIsICJsaW51eC1rZXJuZWxAdmdlci5rZXJuZWwub3JnIiwgImJlOWU0YSJd Received: from smtp.codeaurora.org (ec2-35-166-182-171.us-west-2.compute.amazonaws.com [35.166.182.171]) by smtp-out-n06.prod.us-west-2.postgun.com with SMTP id 5f60f8a4cc683673f91050f5 (version=TLS1.2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256); Tue, 15 Sep 2020 17:23:48 GMT Received: by smtp.codeaurora.org (Postfix, from userid 1001) id 3F761C433F0; Tue, 15 Sep 2020 17:23:48 +0000 (UTC) Received: from [192.168.1.4] (unknown [122.175.29.203]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) (Authenticated sender: gkohli) by smtp.codeaurora.org (Postfix) with ESMTPSA id 684A9C433C8; Tue, 15 Sep 2020 17:23:46 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 smtp.codeaurora.org 684A9C433C8 Authentication-Results: aws-us-west-2-caf-mail-1.web.codeaurora.org; dmarc=none (p=none dis=none) header.from=codeaurora.org Authentication-Results: aws-us-west-2-caf-mail-1.web.codeaurora.org; spf=fail smtp.mailfrom=gkohli@codeaurora.org Subject: Re: [PATCH] trace: Fix race in trace_open and buffer resize call To: Steven Rostedt Cc: mingo@redhat.com, linux-kernel@vger.kernel.org, linux-arm-msm@vger.kernel.org References: <1599199797-25978-1-git-send-email-gkohli@codeaurora.org> <2fe2a843-e2b5-acf8-22e4-7231d24a9382@codeaurora.org> <20200915092353.5b805468@gandalf.local.home> From: Gaurav Kohli Message-ID: <08d6f338-3be3-c5a2-ba4b-0116de9672c2@codeaurora.org> Date: Tue, 15 Sep 2020 22:53:32 +0530 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:68.0) Gecko/20100101 Thunderbird/68.12.0 MIME-Version: 1.0 In-Reply-To: <20200915092353.5b805468@gandalf.local.home> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 9/15/2020 6:53 PM, Steven Rostedt wrote: > On Tue, 15 Sep 2020 10:38:03 +0530 > Gaurav Kohli wrote: > >> >> >>> +void ring_buffer_mutex_release(struct trace_buffer *buffer) >> >>> +{ >> >>> + mutex_unlock(&buffer->mutex); >> >>> +} >> >>> +EXPORT_SYMBOL_GPL(ring_buffer_mutex_release); >> > >> > I really do not like to export these. >> > >> >> Actually available reader lock is not helping >> here(&cpu_buffer->reader_lock), So i took ring buffer mutex lock to >> resolve this(this came on 4.19/5.4), in latest tip it is trace buffer >> lock. Due to this i have exported api. > > I'm saying, why don't you take the buffer->mutex in the > ring_buffer_reset_online_cpus() function? And remove all the protection in > tracing_reset_online_cpus()? Yes, got your point. then we can avoid export. Actually we are seeing issue in older kernel like 4.19/4.14/5.4 and there below patch was not present in stable branches: ommit b23d7a5f4a07 ("ring-buffer: speed up buffer resets by > avoiding synchronize_rcu for each CPU") Actually i have also thought to take mutex lock in ring_buffer_reset_cpu while doing individual cpu reset, but this could cause another problem: Different cpu buffer may have different state, so i have taken lock in tracing_reset_online_cpus. > > void tracing_reset_online_cpus(struct array_buffer *buf) > { > struct trace_buffer *buffer = buf->buffer; > > if (!buffer) > return; > > buf->time_start = buffer_ftrace_now(buf, buf->cpu); > > ring_buffer_reset_online_cpus(buffer); > } > > The reset_online_cpus() is already doing the synchronization, we don't need > to do it twice. > > I believe commit b23d7a5f4a07 ("ring-buffer: speed up buffer resets by > avoiding synchronize_rcu for each CPU") made the synchronization in > tracing_reset_online_cpus() obsolete. > > -- Steve > Yes, with above patch no need to take lock in tracing_reset_online_cpus. -- Qualcomm India Private Limited, on behalf of Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum, a Linux Foundation Collaborative Project.