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[68.147.8.254]) by smtp.gmail.com with ESMTPSA id z22sm3056775pfa.220.2020.11.04.09.03.36 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 04 Nov 2020 09:03:37 -0800 (PST) Date: Wed, 4 Nov 2020 10:03:35 -0700 From: Mathieu Poirier To: Sai Prakash Ranjan Subject: Re: [PATCHv2 2/4] coresight: tmc-etf: Fix NULL ptr dereference in tmc_enable_etf_sink_perf() Message-ID: <20201104170335.GA2892592@xps15> References: <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> <20201023134416.GA2628@hirez.programming.kicks-ass.net> <20201023203729.GA819775@xps15> <70e3a508af119be481c8f0a0acf0a44d@codeaurora.org> <20201030164806.GB1301231@xps15> <85c285361ce1c71b1a8274493aab9ca7@codeaurora.org> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <85c285361ce1c71b1a8274493aab9ca7@codeaurora.org> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20201104_120340_876140_9BC8D783 X-CRM114-Status: GOOD ( 41.31 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Mark Rutland , Suzuki Poulose , Peter Zijlstra , linux-arm-msm@vger.kernel.org, coresight@lists.linaro.org, linux-kernel@vger.kernel.org, Arnaldo Carvalho de Melo , Stephen Boyd , Alexander Shishkin , Ingo Molnar , Namhyung Kim , Jiri Olsa , linux-arm-kernel@lists.infradead.org, Mike Leach Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Fri, Oct 30, 2020 at 10:56:09PM +0530, Sai Prakash Ranjan wrote: > Hi Mathieu, > > On 2020-10-30 22:18, Mathieu Poirier wrote: > > On Fri, Oct 30, 2020 at 01:29:56PM +0530, Sai Prakash Ranjan wrote: > > > Hello guys, > > > > > > On 2020-10-24 02:07, Mathieu Poirier wrote: > > > > On Fri, Oct 23, 2020 at 03:44:16PM +0200, Peter Zijlstra wrote: > > > > > 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. > > > > > > > > I agree with you that --per-thread scenarios are easy to deal with, but > > > > to > > > > support cpu-wide scenarios events must share a sink (because there is > > > > one event > > > > per CPU). CPU-wide support can't be removed because it has been around > > > > for close to a couple of years and heavily used. I also think using the > > > > pid of > > > > the process that created the events, i.e perf, is a good idea. We just > > > > need to > > > > agree on how to gain access to it. > > > > > > > > In Sai's patch you objected to the following: > > > > > > > > > + struct task_struct *task = READ_ONCE(event->owner); > > > > > + > > > > > + if (!task || is_kernel_event(event)) > > > > > > > > Would it be better to use task_nr_pid(current) instead of event->owner? > > > > The end > > > > result will be exactly the same. There is also no need to check the > > > > validity of > > > > @current since it is a user process. > > > > > > > > > > We have devices deployed where these crashes are seen consistently, > > > so for some immediate relief, could we atleast get some fix in this > > > cycle without major design overhaul which would likely take more time. > > > Perhaps my first patch [1] without any check for owner or > > > I can post a new version as Suzuki suggested [2] dropping the export > > > of is_kernel_event(). Then we can always work on top of it based on > > > the > > > conclusion of this discussion, we will atleast not have the systems > > > crash in the meantime, thoughts? > > > > For the time being I think [1], exactly the way it is, is a reasonable > > way > > forward. > > > > Sure, I just checked now and [1] still applies neatly on top of coresight > next branch. > > [1] https://lore.kernel.org/patchwork/patch/1318098/ I have applied both patches that were part of the set. > > Thanks, > Sai > > -- > QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a member > of Code Aurora Forum, hosted by The Linux Foundation _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel