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=-5.4 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE, SPF_PASS,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 D6C17C388F2 for ; Thu, 22 Oct 2020 13:30:27 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 64A04222E9 for ; Thu, 22 Oct 2020 13:30:27 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2900099AbgJVNa0 (ORCPT ); Thu, 22 Oct 2020 09:30:26 -0400 Received: from foss.arm.com ([217.140.110.172]:57780 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2900098AbgJVNa0 (ORCPT ); Thu, 22 Oct 2020 09:30:26 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id B588F101E; Thu, 22 Oct 2020 06:30:25 -0700 (PDT) Received: from [10.57.13.45] (unknown [10.57.13.45]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 49B6A3F66E; Thu, 22 Oct 2020 06:30:23 -0700 (PDT) Subject: Re: [PATCHv2 2/4] coresight: tmc-etf: Fix NULL ptr dereference in tmc_enable_etf_sink_perf() To: Peter Zijlstra , Sai Prakash Ranjan Cc: Mathieu Poirier , Mike Leach , Ingo Molnar , Arnaldo Carvalho de Melo , Mark Rutland , Alexander Shishkin , Jiri Olsa , Namhyung Kim , coresight@lists.linaro.org, Stephen Boyd , linux-arm-msm@vger.kernel.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org References: <20201022113214.GD2611@hirez.programming.kicks-ass.net> From: Suzuki Poulose Message-ID: Date: Thu, 22 Oct 2020 14:30:21 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.3.2 MIME-Version: 1.0 In-Reply-To: <20201022113214.GD2611@hirez.programming.kicks-ass.net> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-GB Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-arm-msm@vger.kernel.org On 10/22/20 12:32 PM, Peter Zijlstra wrote: > On Thu, Oct 22, 2020 at 04:27:52PM +0530, Sai Prakash Ranjan wrote: > >> Looking at the ETR and other places in the kernel, ETF and the >> ETB are the only places trying to dereference the task(owner) >> in tmc_enable_etf_sink_perf() which is also called from the >> sched_in path as in the call trace. > >> @@ -391,6 +392,10 @@ static void *tmc_alloc_etf_buffer(struct coresight_device *csdev, >> { >> int node; >> struct cs_buffers *buf; >> + struct task_struct *task = READ_ONCE(event->owner); >> + >> + if (!task || is_kernel_event(event)) >> + return NULL; > > > This is *wrong*... why do you care about who owns the events? > This is due to the special case of the CoreSight configuration, where a "sink" (where the trace data is captured) is shared by multiple Trace units. So, we could share the "sink" for multiple trace units if they are tracing the events that belong to the same "perf" session. (The userspace tool could decode the trace data based on the TraceID in the trace packets). Is there a better way to do this ? Suzuki