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=-3.9 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 19372C4363A for ; Fri, 23 Oct 2020 13:44:34 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id AB7D921527 for ; Fri, 23 Oct 2020 13:44:33 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="tAeBy66w" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1750019AbgJWNod (ORCPT ); Fri, 23 Oct 2020 09:44:33 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:50812 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750018AbgJWNoc (ORCPT ); Fri, 23 Oct 2020 09:44:32 -0400 Received: from casper.infradead.org (casper.infradead.org [IPv6:2001:8b0:10b:1236::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id A7453C0613CE; Fri, 23 Oct 2020 06:44:32 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=627oe94ZLeKyjbn+qyvUY++lrQo5+wHp1qVKRnwOyEA=; b=tAeBy66w9joU2PrbRcza5JTXle OQ1GNbtKm1kuwALnI3n5XGE48bmTbzeIUI3woO3q/FJzb5CMWMcPWAr2mw4nh/tkvhoTmvRMse5M5 398H/FWTpl07yUabCgpJ3R43gitI0mK0dEzUUNo/vAl9B5F0hjZPr9XWXtd9ythKH1x4j8HnmvTpV XxR/NkHFLrB/KjBpbKKGC7ui/GCLc9dXVwMVVqGcz9iaJ2qK02ANhTToLcwLuLZskBzmufSxPUTRY H17rSXqWnece4UGf2Oj722qSORrug+kLR5xQI9znH+pwqIUVHki8yvnZtkFe6g3jq+X4sGqr+jcQ2 dmRyGHmA==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=noisy.programming.kicks-ass.net) by casper.infradead.org with esmtpsa (Exim 4.92.3 #3 (Red Hat Linux)) id 1kVxMh-0007Dn-0M; Fri, 23 Oct 2020 13:44:19 +0000 Received: from hirez.programming.kicks-ass.net (hirez.programming.kicks-ass.net [192.168.1.225]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id CF997304D28; Fri, 23 Oct 2020 15:44:16 +0200 (CEST) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id B819D23268BA4; Fri, 23 Oct 2020 15:44:16 +0200 (CEST) Date: Fri, 23 Oct 2020 15:44:16 +0200 From: Peter Zijlstra To: Suzuki Poulose Cc: Mathieu Poirier , Sai Prakash Ranjan , 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 Subject: Re: [PATCHv2 2/4] coresight: tmc-etf: Fix NULL ptr dereference in tmc_enable_etf_sink_perf() Message-ID: <20201023134416.GA2628@hirez.programming.kicks-ass.net> References: <788706f2-0670-b7b6-a153-3ec6f16e0f2e@arm.com> <20201022212033.GA646497@xps15> <20201023073905.GM2611@hirez.programming.kicks-ass.net> <174e6461-4d46-cb65-c094-c06ee3b21568@arm.com> <20201023094115.GR2611@hirez.programming.kicks-ass.net> <20201023105431.GM2594@hirez.programming.kicks-ass.net> <2457de8f-8bc3-b350-fdc7-61276da31ce6@arm.com> <20201023131628.GY2628@hirez.programming.kicks-ass.net> <728fd89c-78f2-0c5c-0443-c91c62b02f0e@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <728fd89c-78f2-0c5c-0443-c91c62b02f0e@arm.com> Precedence: bulk List-ID: X-Mailing-List: linux-arm-msm@vger.kernel.org On Fri, Oct 23, 2020 at 02:29:54PM +0100, Suzuki Poulose wrote: > On 10/23/20 2:16 PM, Peter Zijlstra wrote: > > On Fri, Oct 23, 2020 at 01:56:47PM +0100, Suzuki Poulose wrote: > > > That way another session could use the same sink if it is free. i.e > > > > > > perf record -e cs_etm/@sink0/u --per-thread app1 > > > > > > and > > > > > > perf record -e cs_etm/@sink0/u --per-thread app2 > > > > > > both can work as long as the sink is not used by the other session. > > > > Like said above, if sink is shared between CPUs, that's going to be a > > trainwreck :/ Why do you want that? > > That ship has sailed. That is how the current generation of systems are, > unfortunately. But as I said, this is changing and there are guidelines > in place to avoid these kind of topologies. With the future > technologies, this will be completely gone. I understand that the hardware is like that, but why do you want to support this insanity in software? If you only allow a single sink user (group) at the same time, your problem goes away. Simply disallow the above scenario, do not allow concurrent sink users if sinks are shared like this. Have the perf-record of app2 above fail because the sink is in-user already. Only if the hardware has per-CPU sinks can you allow this.