Re: [PATCH bpf-next v4 1/5] bpf: Add bpf_link support for sk_msg and sk_skb progs

[John Fastabend <john.fastabend@gmail.com>]

Yonghong Song wrote:
> 
> On 4/5/24 8:19 AM, John Fastabend wrote:
> > Yonghong Song wrote:
> >> Add bpf_link support for sk_msg and sk_skb programs. We have an
> >> internal request to support bpf_link for sk_msg programs so user
> >> space can have a uniform handling with bpf_link based libbpf
> >> APIs. Using bpf_link based libbpf API also has a benefit which
> >> makes system robust by decoupling prog life cycle and
> >> attachment life cycle.
> >>
> >> Signed-off-by: Yonghong Song <yonghong.song@linux.dev>
> >> ---
> >>   include/linux/bpf.h            |   6 +
> >>   include/linux/skmsg.h          |   4 +
> >>   include/uapi/linux/bpf.h       |   5 +
> >>   kernel/bpf/syscall.c           |   4 +
> >>   net/core/sock_map.c            | 268 ++++++++++++++++++++++++++++++++-
> >>   tools/include/uapi/linux/bpf.h |   5 +
> >>   6 files changed, 284 insertions(+), 8 deletions(-)
> >>
> > LGTM one question below.
> >
> >> +/* Handle the following two cases:
> >> + * case 1: link != NULL, prog != NULL, old != NULL
> >> + * case 2: link != NULL, prog != NULL, old == NULL
> >> + */
> >> +static int sock_map_link_update_prog(struct bpf_link *link,
> >> +				     struct bpf_prog *prog,
> >> +				     struct bpf_prog *old)
> >> +{
> >> +	const struct sockmap_link *sockmap_link = container_of(link, struct sockmap_link, link);
> >> +	struct bpf_prog **pprog;
> >> +	struct bpf_link **plink;
> >> +	int ret = 0;
> >> +
> >> +	mutex_lock(&sockmap_mutex);
> >> +
> >> +	/* If old prog is not NULL, ensure old prog is the same as link->prog. */
> >> +	if (old && link->prog != old) {
> >> +		ret = -EINVAL;
> >> +		goto out;
> >> +	}
> >> +	/* Ensure link->prog has the same type/attach_type as the new prog. */
> >> +	if (link->prog->type != prog->type ||
> >> +	    link->prog->expected_attach_type != prog->expected_attach_type) {
> >> +		ret = -EINVAL;
> >> +		goto out;
> >> +	}
> >> +
> >> +	ret = sock_map_prog_lookup(sockmap_link->map, &pprog,
> >> +				   sockmap_link->attach_type);
> >> +	if (ret)
> >> +		goto out;
> >> +
> >> +	/* Ensure the same link between the one in map and the passed-in. */
> >> +	ret = sock_map_link_lookup(sockmap_link->map, &plink, link, false,
> >> +				   sockmap_link->attach_type);
> >> +	if (ret)
> >> +		goto out;
> >> +
> >> +	if (old) {
> >> +		ret = psock_replace_prog(pprog, prog, old);
> >> +		goto out;
> >> +	}
> >> +
> >> +	psock_set_prog(pprog, prog);
> >> +
> >> +out:
> >> +	if (!ret) {
> >> +		bpf_prog_inc(prog);
> >> +		old = xchg(&link->prog, prog);
> >> +		bpf_prog_put(old);
> > Need to check old? I don't think we can clal bpf_prog_put on null?
> >
> >    if (old)
> >       bpf_prog_put(old)
> 
> The 'old' here represents the *old* link->prog program and
> link->prog should not be NULL at this point.

Ah ok. Maybe instead of using the input old var make it
explicit?

    if (!ret) {
       struct bpf_prog *old_link;

       bpf_prog_inc(prog);
       old_link = xchg(&link->prog, prog);
       bpf_prog_put(old)
    }

Is a bit more obious to me at least. Up to you I have a slight preference
for the explicit more verbose above.

Otherwise for the series.

Reviewed-by: John Fastabend <john.fastabend@gmail.com>