linux-kernel - Re: [PATCH 27/42] perf tools: Protect dso symbol loading using a mutex

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Date:	Thu, 29 Jan 2015 21:48:32 +0900
From:	Namhyung Kim <namhyung@...nel.org>
To:	Arnaldo Carvalho de Melo <acme@...nel.org>
Cc:	Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Jiri Olsa <jolsa@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>,
	David Ahern <dsahern@...il.com>,
	Adrian Hunter <adrian.hunter@...el.com>,
	Andi Kleen <andi@...stfloor.org>,
	Stephane Eranian <eranian@...gle.com>,
	Frederic Weisbecker <fweisbec@...il.com>
Subject: Re: [PATCH 27/42] perf tools: Protect dso symbol loading using a mutex

Hi Arnaldo,

On Thu, Jan 29, 2015 at 9:34 PM, Arnaldo Carvalho de Melo
<acme@...nel.org> wrote:
> Em Thu, Jan 29, 2015 at 05:07:08PM +0900, Namhyung Kim escreveu:
>> When multi-thread support for perf report is enabled, it's possible to
>> access a dso concurrently.  Add a new pthread_mutex to protect it from
>> concurrent dso__load().
>>
>> Signed-off-by: Namhyung Kim <namhyung@...nel.org>
>> ---
>>  tools/perf/util/dso.c    |  2 ++
>>  tools/perf/util/dso.h    |  1 +
>>  tools/perf/util/symbol.c | 34 ++++++++++++++++++++++++----------
>>  3 files changed, 27 insertions(+), 10 deletions(-)
>>
>> diff --git a/tools/perf/util/dso.c b/tools/perf/util/dso.c
>> index 45be944d450a..3da75816b8f8 100644
>> --- a/tools/perf/util/dso.c
>> +++ b/tools/perf/util/dso.c
>> @@ -888,6 +888,7 @@ struct dso *dso__new(const char *name)
>>               RB_CLEAR_NODE(&dso->rb_node);
>>               INIT_LIST_HEAD(&dso->node);
>>               INIT_LIST_HEAD(&dso->data.open_entry);
>> +             pthread_mutex_init(&dso->lock, NULL);
>>       }
>>
>>       return dso;
>> @@ -917,6 +918,7 @@ void dso__delete(struct dso *dso)
>>       dso_cache__free(&dso->data.cache);
>>       dso__free_a2l(dso);
>>       zfree(&dso->symsrc_filename);
>> +     pthread_mutex_destroy(&dso->lock);
>>       free(dso);
>>  }
>>
>> diff --git a/tools/perf/util/dso.h b/tools/perf/util/dso.h
>> index 3782c82c6e44..ac753594a469 100644
>> --- a/tools/perf/util/dso.h
>> +++ b/tools/perf/util/dso.h
>> @@ -102,6 +102,7 @@ struct dsos {
>>  };
>>
>>  struct dso {
>> +     pthread_mutex_t  lock;
>>       struct list_head node;
>>       struct rb_node   rb_node;       /* rbtree node sorted by long name */
>>       struct rb_root   symbols[MAP__NR_TYPES];
>> diff --git a/tools/perf/util/symbol.c b/tools/perf/util/symbol.c
>> index a69066865a55..714e20c99354 100644
>> --- a/tools/perf/util/symbol.c
>> +++ b/tools/perf/util/symbol.c
>> @@ -1357,12 +1357,22 @@ int dso__load(struct dso *dso, struct map *map, symbol_filter_t filter)
>>       struct symsrc *syms_ss = NULL, *runtime_ss = NULL;
>>       bool kmod;
>>
>> -     dso__set_loaded(dso, map->type);
>> +     pthread_mutex_lock(&dso->lock);
>> +
>> +     /* check again under the dso->lock */
>
> Again? Where was it first checked?

Please see map__load().


> Perhaps we should lock there, so that
> we don't have to do two checks, one unlocked, the other locked?

Hmm.. maybe.  I just keep it to avoid locking overhead since it'll be
called whenever it searches symbols during preprocessing.  I didn't
measure the overhead but it could be huge IMHO.

Thanks,
Namhyung


>
>> +     if (dso__loaded(dso, map->type)) {
>> +             ret = 1;
>> +             goto out;
>> +     }
>> +
>
> - Arnaldo
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