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Date:   Fri, 23 Oct 2020 11:41:15 +0200
From:   Peter Zijlstra <peterz@infradead.org>
To:     Suzuki Poulose <suzuki.poulose@arm.com>
Cc:     Mathieu Poirier <mathieu.poirier@linaro.org>,
        Sai Prakash Ranjan <saiprakash.ranjan@codeaurora.org>,
        Mike Leach <mike.leach@linaro.org>,
        Ingo Molnar <mingo@redhat.com>,
        Arnaldo Carvalho de Melo <acme@kernel.org>,
        Mark Rutland <mark.rutland@arm.com>,
        Alexander Shishkin <alexander.shishkin@linux.intel.com>,
        Jiri Olsa <jolsa@redhat.com>,
        Namhyung Kim <namhyung@kernel.org>, coresight@lists.linaro.org,
        Stephen Boyd <swboyd@chromium.org>,
        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()
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References: <cover.1603363729.git.saiprakash.ranjan@codeaurora.org>
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On Fri, Oct 23, 2020 at 09:49:53AM +0100, Suzuki Poulose wrote:
> On 10/23/20 8:39 AM, Peter Zijlstra wrote:

> > So then I don't understand the !->owner issue, that only happens when
> > the task dies, which cannot be concurrent with event creation. Are you
> 
> Part of the patch from Sai, fixes this by avoiding the dereferencing
> after event creation (by caching it). But the kernel events needs
> fixing.

I'm fundamentally failing here. Creating a link to the sink is strictly
event-creation time. Why would you ever need it again later? Later you
already have the sink setup.