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Date:   Mon, 6 Apr 2020 13:47:40 +0100
From:   Al Viro <viro@zeniv.linux.org.uk>
To:     Jiri Olsa <jolsa@redhat.com>
Cc:     Jiri Olsa <jolsa@kernel.org>, Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>, netdev@vger.kernel.org,
        bpf@vger.kernel.org, Yonghong Song <yhs@fb.com>,
        Martin KaFai Lau <kafai@fb.com>,
        David Miller <davem@redhat.com>,
        John Fastabend <john.fastabend@gmail.com>,
        Jesper Dangaard Brouer <hawk@kernel.org>,
        Wenbo Zhang <ethercflow@gmail.com>,
        KP Singh <kpsingh@chromium.org>,
        Andrii Nakryiko <andriin@fb.com>, bgregg@netflix.com
Subject: Re: [RFC 0/3] bpf: Add d_path helper
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On Mon, Apr 06, 2020 at 11:09:18AM +0200, Jiri Olsa wrote:

> it could be called as bpf helper from any place we could put
> the trampoline probe on.. so most of the kernel functions
> (at entry or exit) .. we can make checks, like for context
> before we allow to call it

Hard NAK, then.  If you can insert its call at the entry to
e.g. umount_tree(), you will get deadlocks.  The same for e.g.
select_collect() (same effect on a different seqlock).