linux-kernel - Re: [PATCH v5 perf, bpf-next 3/7] perf, bpf: introduce PERF_RECORD_BPF

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Message-ID: <20190108184116.GC30894@hirez.programming.kicks-ass.net>
Date:   Tue, 8 Jan 2019 19:41:16 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Song Liu <songliubraving@...com>
Cc:     linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
        acme@...nel.org, ast@...nel.org, daniel@...earbox.net,
        kernel-team@...com
Subject: Re: [PATCH v5 perf, bpf-next 3/7] perf, bpf: introduce
 PERF_RECORD_BPF_EVENT

On Thu, Dec 20, 2018 at 10:29:00AM -0800, Song Liu wrote:
> @@ -986,9 +987,35 @@ enum perf_event_type {
>  	 */
>  	PERF_RECORD_KSYMBOL			= 17,
>  
> +	/*
> +	 * Record bpf events:
> +	 *  enum perf_bpf_event_type {
> +	 *	PERF_BPF_EVENT_UNKNOWN		= 0,
> +	 *	PERF_BPF_EVENT_PROG_LOAD	= 1,
> +	 *	PERF_BPF_EVENT_PROG_UNLOAD	= 2,
> +	 *  };
> +	 *
> +	 * struct {
> +	 *	struct perf_event_header	header;
> +	 *	u16				type;
> +	 *	u16				flags;
> +	 *	u32				id;
> +	 *	u8				tag[BPF_TAG_SIZE];
> +	 *	struct sample_id		sample_id;
> +	 * };
> +	 */
> +	PERF_RECORD_BPF_EVENT			= 18,
> +

Elsewhere today, I raised the point that by the time (however short
interval) userspace gets around to reading this event, the actual
program could be gone again.

In this case the program has been with us for a very short period
indeed; but it could still have generated some samples or otherwise
generated trace data.

It was suggested to allow pinning modules/programs to avoid this
situation, but that of course has other undesirable effects, such as a
trivial DoS.

A truly horrible hack would be to include an open filedesc in the event
that needs closing to release the resource, but I'm sorry for even
suggesting that **shudder**.

Do we have any sane ideas?