linux-kernel - Re: [PATCH 1/3] perf tools: Protect reading thread's namespace

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Message-ID: <20190522131832.GB30271@kernel.org>
Date:   Wed, 22 May 2019 10:18:32 -0300
From:   Arnaldo Carvalho de Melo <arnaldo.melo@...il.com>
To:     Namhyung Kim <namhyung@...nel.org>
Cc:     Jiri Olsa <jolsa@...hat.com>, LKML <linux-kernel@...r.kernel.org>,
        Krister Johansen <kjlx@...pleofstupid.com>,
        Hari Bathini <hbathini@...ux.vnet.ibm.com>
Subject: Re: [PATCH 1/3] perf tools: Protect reading thread's namespace

Em Wed, May 22, 2019 at 02:32:48PM +0900, Namhyung Kim escreveu:
> It seems that the current code lacks holding the namespace lock in
> thread__namespaces().  Otherwise it can see inconsistent results.
> 
> Signed-off-by: Namhyung Kim <namhyung@...nel.org>
> ---
>  tools/perf/util/thread.c | 15 +++++++++++++--
>  1 file changed, 13 insertions(+), 2 deletions(-)
> 
> diff --git a/tools/perf/util/thread.c b/tools/perf/util/thread.c
> index 403045a2bbea..b413ba5b9835 100644
> --- a/tools/perf/util/thread.c
> +++ b/tools/perf/util/thread.c
> @@ -133,7 +133,7 @@ void thread__put(struct thread *thread)
>  	}
>  }
>  
> -struct namespaces *thread__namespaces(const struct thread *thread)
> +static struct namespaces *__thread__namespaces(const struct thread *thread)
>  {
>  	if (list_empty(&thread->namespaces_list))
>  		return NULL;
> @@ -141,10 +141,21 @@ struct namespaces *thread__namespaces(const struct thread *thread)
>  	return list_first_entry(&thread->namespaces_list, struct namespaces, list);
>  }
>  
> +struct namespaces *thread__namespaces(const struct thread *thread)
> +{
> +	struct namespaces *ns;
> +
> +	down_read((struct rw_semaphore *)&thread->namespaces_lock);
> +	ns = __thread__namespaces(thread);
> +	up_read((struct rw_semaphore *)&thread->namespaces_lock);
> +

Humm, so we need to change thread__namespaces() to remove that const
instead of throwing it away with that cast, right?

- Arnaldo

> +	return ns;
> +}
> +
>  static int __thread__set_namespaces(struct thread *thread, u64 timestamp,
>  				    struct namespaces_event *event)
>  {
> -	struct namespaces *new, *curr = thread__namespaces(thread);
> +	struct namespaces *new, *curr = __thread__namespaces(thread);
>  
>  	new = namespaces__new(event);
>  	if (!new)
> -- 
> 2.21.0.1020.gf2820cf01a-goog

-- 

- Arnaldo