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Sender: Namhyung Kim <namhyung@gmail.com>
From:   Namhyung Kim <namhyung@kernel.org>
To:     Namhyung Kim <namhyung@kernel.org>,
        Arnaldo Carvalho de Melo <acme@kernel.org>,
        Jiri Olsa <jolsa@kernel.org>
Cc:     LKML <linux-kernel@vger.kernel.org>,
        Ingo Molnar <mingo@kernel.org>, Hao Luo <haoluo@google.com>,
        Song Liu <song@kernel.org>,
        Adrian Hunter <adrian.hunter@intel.com>, bpf@vger.kernel.org,
        linux-perf-users@vger.kernel.org, Ian Rogers <irogers@google.com>,
        Peter Zijlstra <peterz@infradead.org>
Subject: Re: [PATCH v3 1/3] perf lock contention: Clear lock addr after use
Date:   Thu, 26 Oct 2023 10:11:12 -0700
Message-ID: <169833996388.1181734.6181786783343850640.b4-ty@kernel.org>
In-Reply-To: <20231020204741.1869520-1-namhyung@kernel.org>
References: <20231020204741.1869520-1-namhyung@kernel.org>
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On Fri, 20 Oct 2023 13:47:39 -0700, Namhyung Kim wrote:
> It checks the current lock to calculated the delta of contention time.
> The address is saved in the tstamp map which is allocated at begining of
> contention and released at end of contention.
> 
> But it's possible for bpf_map_delete_elem() to fail.  In that case, the
> element in the tstamp map kept for the current lock and it makes the
> next contention for the same lock tracked incorrectly.  Specificially
> the next contention begin will see the existing element for the task and
> it'd just return.  Then the next contention end will see the element and
> calculate the time using the timestamp for the previous begin.
> 
> [...]

Applied to perf-tools-next, thanks!