Date: Fri, 17 Jul 2015 13:06:23 +0200
From: Peter Zijlstra <peterz@infradead.org>
To: kaixu xia <xiakaixu@huawei.com>
Cc: ast@plumgrid.com, davem@davemloft.net, acme@kernel.org, mingo@redhat.com,
        masami.hiramatsu.pt@hitachi.com, jolsa@kernel.org, wangnan0@huawei.com,
        linux-kernel@vger.kernel.org, pi3orama@163.com, hekuang@huawei.com
Subject: Re: [RFC PATCH 3/6] bpf: Save the pointer to struct perf_event to map
Message-ID: <20150717110623.GK12596@twins.programming.kicks-ass.net>
References: <1437129816-13176-1-git-send-email-xiakaixu@huawei.com>
 <1437129816-13176-4-git-send-email-xiakaixu@huawei.com>
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On Fri, Jul 17, 2015 at 06:43:33PM +0800, kaixu xia wrote:
> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index e965cfa..c4e34b7 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -8582,6 +8582,28 @@ void perf_event_delayed_put(struct task_struct *task)
>  		WARN_ON_ONCE(task->perf_event_ctxp[ctxn]);
>  }
>  
> +struct perf_event *perf_event_get(unsigned int fd)
> +{
> +	struct perf_event *event;
> +	struct fd f;
> +
> +	f = fdget(fd);
> +
> +	if (!f.file)
> +		return ERR_PTR(-EBADF);
> +
> +	if (f.file->f_op != &perf_fops) {
> +		fdput(f);
> +		return ERR_PTR(-EINVAL);
> +	}
> +
> +	event = f.file->private_data;
> +
> +	fdput(f);
> +
> +	return event;
> +}

And what is stopping userspace from closing those FDs while you're using
them?
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