linux-kernel - Re: [PATCH RFC V4 1/6] perf tools: lock to protect namespaces and comm list

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Message-ID: <20171002193453.GD2869@kernel.org>
Date:   Mon, 2 Oct 2017 16:34:53 -0300
From:   Arnaldo Carvalho de Melo <acme@...nel.org>
To:     "Liang, Kan" <kan.liang@...el.com>
Cc:     "peterz@...radead.org" <peterz@...radead.org>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "jolsa@...nel.org" <jolsa@...nel.org>,
        "namhyung@...nel.org" <namhyung@...nel.org>,
        "Hunter, Adrian" <adrian.hunter@...el.com>,
        "Odzioba, Lukasz" <lukasz.odzioba@...el.com>,
        "wangnan0@...wei.com" <wangnan0@...wei.com>,
        "hekuang@...wei.com" <hekuang@...wei.com>,
        "ast@...nel.org" <ast@...nel.org>,
        "ak@...ux.intel.com" <ak@...ux.intel.com>
Subject: Re: [PATCH RFC V4 1/6] perf tools: lock to protect namespaces and
 comm list

Em Mon, Oct 02, 2017 at 07:14:10PM +0000, Liang, Kan escreveu:
> > Em Fri, Sep 29, 2017 at 07:47:52AM -0700, kan.liang@...el.com escreveu:
> > > From: Kan Liang <kan.liang@...el.com>
> > >
> > > Add two locks to protect namespaces_list and comm_list.
> > >
> > > The lock is only needed for multithreaded code, so using mutex
> > > wrappers provided by perf tool.
> > >
> > > Not all the comm_list/namespaces_list accessing are protected, e.g.
> > > thread__exec_comm. Because the multithread code for perf top event
> > > synthesizing does not touch them. They don't need a lock.
> > 
> > They don't need a lock _now_, ok I think we can proceed that way, this cset
> > should serve as a warning to people working in further multithreading perf.
> > 
> 
> Do I need to add some comments in the code to give a warning?

Maybe, but then one can use 'git blame' and see the comments on the
patch introducing the locking.

BTW, I'm applied and tested it, pushed to acme/perf/core.

- Arnaldo