netdev - Re: BPF program attached on BPF map function (read,write) is not working?

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Date:   Mon, 13 Apr 2020 20:04:24 -0700
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     "Daniel T. Lee" <danieltimlee@...il.com>
Cc:     bpf <bpf@...r.kernel.org>, netdev <netdev@...r.kernel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Alexei Starovoitov <ast@...nel.org>,
        Andrii Nakryiko <andrii.nakryiko@...il.com>,
        Martin KaFai Lau <kafai@...com>
Subject: Re: BPF program attached on BPF map function (read,write) is not
 working?

On Thu, Apr 09, 2020 at 12:26:37PM +0900, Daniel T. Lee wrote:
> 
> So, I think this 'unable to attach bpf program on BPF map function (read,write)'
> is a bug. Or is it desired action?

desired action.

> If it is a bug, bpf_{enable|disable}_instrumentation() should only
> cover stackmap
> as the upper commit intended. Not sure but adding another flag for
> lock might work?
> 
> Or if this is an desired action, this should be covered at
> documentation with a limitation
> and tracex6 sample has to be removed.

Right. That test has to be fixed.
These two old commits:
commit 020a32d9581a ("bpf: add a test case for helper bpf_perf_event_read_value")
commit 41e9a8046c92 ("samples/bpf: add tests for more perf event types")
attached kprobe bpf to inner map accessors get_next and lookup.
That's safe only for a subset of map types and not allowed in general.
It works for hash and array because they don't take locks in these operations.