linux-kernel - Re: perf_event_detach_bpf

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Message-ID: <ZxewvPQX7bq40PK3@krava>
Date: Tue, 22 Oct 2024 16:03:40 +0200
From: Jiri Olsa <olsajiri@...il.com>
To: Peter Zijlstra <peterz@...radead.org>
Cc: andrii@...nel.org, yhs@...com, linux-kernel@...r.kernel.org,
	daniel@...earbox.net, sean@...s.org
Subject: Re: perf_event_detach_bpf_prog() broken?

On Tue, Oct 22, 2024 at 01:16:38PM +0200, Peter Zijlstra wrote:
> Hi guys,
> 
> Per commit 170a7e3ea070 ("bpf: bpf_prog_array_copy() should return
> -ENOENT if exclude_prog not found") perf_event_detach_bpf_prog() can now
> return without doing bpf_prog_put() and leaving event->prog set.
> 
> This is very 'unexpected' behaviour.
> 
> I'm not sure what's sane from the BPF side of things here, but leaving
> event->prog set is really rather unexpected.
> 
> Help?

IIUC the ENOENT should never happen in perf event context, so not
sure why we have that check.. also does not seem to be used from
lirc code, Sean?

perf_event_detach_bpf_prog is called when the event is being freed
so I think we should always put and clear the event->prog

jirka