linux-kernel - Re: [PATCH v3 09/18] perf ui: Update use of pthread mutex

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Message-ID: <bdbd520a-b1c4-01c4-18bb-f1c2b553371d@intel.com>
Date:   Sat, 27 Aug 2022 10:11:19 +0300
From:   Adrian Hunter <adrian.hunter@...el.com>
To:     Ian Rogers <irogers@...gle.com>, Namhyung Kim <namhyung@...nel.org>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
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Subject: Re: [PATCH v3 09/18] perf ui: Update use of pthread mutex

On 26/08/22 23:52, Ian Rogers wrote:
> On Fri, Aug 26, 2022 at 1:40 PM Namhyung Kim <namhyung@...nel.org> wrote:
>>
>> On Fri, Aug 26, 2022 at 12:21 PM Adrian Hunter <adrian.hunter@...el.com> wrote:
>>>
>>> On 26/08/22 22:00, Namhyung Kim wrote:
>>>> On Fri, Aug 26, 2022 at 11:53 AM Adrian Hunter <adrian.hunter@...el.com> wrote:
>>>>> Below seems adequate for now, at least logically, but maybe it
>>>>> would confuse clang thread-safety analysis?
>>>>
>>>> I think it's not just about locks, the exit_browser should bail out early
>>>> if the setup code was not called.
>>>
>>> In those cases, use_browser is 0 or -1 unless someone has inserted
>>> an invalid perf config like "tui.script=on" or "gtk.script=on".
>>> So currently, in cases where exit_browser() is called without
>>> setup_browser(), it does nothing.  Which means it is only the
>>> unconditional mutex_destroy() that needs to be conditional.
>>
>> Yeah there's a possibility that it can be called with > 0 use_browser
>> on some broken config or something.  So I think it's safer and better
>> for future changes.
> 
> I'd thought about a:
> static bool ui__lock_initialized;
> but the issue is shouldn't it be atomic?

No, it is only accessed from the main thread.