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

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Message-ID: <20150129123445.GS7220@kernel.org>
Date:	Thu, 29 Jan 2015 09:34:45 -0300
From:	Arnaldo Carvalho de Melo <acme@...nel.org>
To:	Namhyung Kim <namhyung@...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

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

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

- Arnaldo
--
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