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

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Message-ID: <b0f86189-be17-d1e7-d23c-692eeee2b5ec@intel.com>
Date:   Fri, 26 Aug 2022 22:20:28 +0300
From:   Adrian Hunter <adrian.hunter@...el.com>
To:     Namhyung Kim <namhyung@...nel.org>
Cc:     Ian Rogers <irogers@...gle.com>,
        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>,
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        bpf <bpf@...r.kernel.org>, llvm@...ts.linux.dev
Subject: Re: [PATCH v3 09/18] perf ui: Update use of pthread mutex

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.

> 
> Thanks,
> Namhyung
> 
> 
>>
>> diff --git a/tools/perf/ui/setup.c b/tools/perf/ui/setup.c
>> index 25ded88801a3..6d81be6a349e 100644
>> --- a/tools/perf/ui/setup.c
>> +++ b/tools/perf/ui/setup.c
>> @@ -73,9 +73,17 @@ int stdio__config_color(const struct option *opt __maybe_unused,
>>         return 0;
>>  }
>>
>> +/*
>> + * exit_browser() can get called without setup_browser() having been called
>> + * first, so it is necessary to keep track of whether ui__lock has been
>> + * initialized.
>> + */
>> +static bool ui__lock_initialized;
>> +
>>  void setup_browser(bool fallback_to_pager)
>>  {
>>         mutex_init(&ui__lock);
>> +       ui__lock_initialized = true;
>>         if (use_browser < 2 && (!isatty(1) || dump_trace))
>>                 use_browser = 0;
>>
>> @@ -118,5 +126,6 @@ void exit_browser(bool wait_for_ok)
>>         default:
>>                 break;
>>         }
>> -       mutex_destroy(&ui__lock);
>> +       if (ui__lock_initialized)
>> +               mutex_destroy(&ui__lock);
>>  }
>>