netdev - Re: [PATCH bpf-next v7 03/11] bpf: per-cgroup lsm flavor

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Date:   Mon, 23 May 2022 22:57:06 -0700
From:   Martin KaFai Lau <kafai@...com>
To:     Stanislav Fomichev <sdf@...gle.com>
Cc:     netdev@...r.kernel.org, bpf@...r.kernel.org, ast@...nel.org,
        daniel@...earbox.net, andrii@...nel.org
Subject: Re: [PATCH bpf-next v7 03/11] bpf: per-cgroup lsm flavor

On Mon, May 23, 2022 at 07:15:03PM -0700, Stanislav Fomichev wrote:
> > > +             return;
> > > +
> > > +     WARN_ON_ONCE(__bpf_trampoline_unlink_prog(&shim_link->tramp_link, shim_link->tr));
> > > +     kfree(shim_link);
> > How about shim_link->tramp_link.link.prog, is the prog freed ?
> >
> > Considering the bpf_link_put() does bpf_prog_put(link->prog).
> > Is there a reason the bpf_link_put() not used and needs to
> > manage its own shim_link->refcnt here ?
> 
> Good catch, I've missed the bpf_prog_put(link->prog) part. Let me see
> if I can use the link's refcnt, it seems like I can define my own
> link->ops->dealloc to call __bpf_trampoline_unlink_prog and the rest
> will be taken care of.
>From looking at bpf_link_free(), link->ops->release may be a better one
because the link->ops->release() will still need to use the shim_prog
(e.g. shim_prog->aux->cgroup_atype).