From: "Björn Töpel" <bjorn.topel@intel.com>
To: John Fastabend <john.fastabend@gmail.com>,
Maciej Fijalkowski <maciej.fijalkowski@intel.com>,
daniel@iogearbox.net, ast@kernel.org, bpf@vger.kernel.org,
netdev@vger.kernel.org
Cc: andrii@kernel.org, toke@redhat.com, magnus.karlsson@intel.com,
ciara.loftus@intel.com
Subject: Re: [PATCH bpf-next 1/3] libbpf: xsk: use bpf_link
Date: Tue, 16 Feb 2021 10:20:52 +0100 [thread overview]
Message-ID: <4a52d09a-363b-e69e-41d3-7918f0204901@intel.com> (raw)
In-Reply-To: <602ade57ddb9c_3ed41208a1@john-XPS-13-9370.notmuch>
On 2021-02-15 21:49, John Fastabend wrote:
> Maciej Fijalkowski wrote:
>> Currently, if there are multiple xdpsock instances running on a single
>> interface and in case one of the instances is terminated, the rest of
>> them are left in an inoperable state due to the fact of unloaded XDP
>> prog from interface.
>>
>> To address that, step away from setting bpf prog in favour of bpf_link.
>> This means that refcounting of BPF resources will be done automatically
>> by bpf_link itself.
>>
>> When setting up BPF resources during xsk socket creation, check whether
>> bpf_link for a given ifindex already exists via set of calls to
>> bpf_link_get_next_id -> bpf_link_get_fd_by_id -> bpf_obj_get_info_by_fd
>> and comparing the ifindexes from bpf_link and xsk socket.
>>
>> If there's no bpf_link yet, create one for a given XDP prog and unload
>> explicitly existing prog if XDP_FLAGS_UPDATE_IF_NOEXIST is not set.
>>
>> If bpf_link is already at a given ifindex and underlying program is not
>> AF-XDP one, bail out or update the bpf_link's prog given the presence of
>> XDP_FLAGS_UPDATE_IF_NOEXIST.
>>
>> Signed-off-by: Maciej Fijalkowski <maciej.fijalkowski@intel.com>
>> ---
>> tools/lib/bpf/xsk.c | 143 +++++++++++++++++++++++++++++++++++++-------
>> 1 file changed, 122 insertions(+), 21 deletions(-)
>
> [...]
>
>> +static int xsk_create_bpf_link(struct xsk_socket *xsk)
>> +{
>> + /* bpf_link only accepts XDP_FLAGS_MODES, but xsk->config.xdp_flags
>> + * might have set XDP_FLAGS_UPDATE_IF_NOEXIST
>> + */
>> + DECLARE_LIBBPF_OPTS(bpf_link_create_opts, opts,
>> + .flags = (xsk->config.xdp_flags & XDP_FLAGS_MODES));
>> + struct xsk_ctx *ctx = xsk->ctx;
>> + __u32 prog_id;
>> + int link_fd;
>> + int err;
>> +
>> + /* for !XDP_FLAGS_UPDATE_IF_NOEXIST, unload the program first, if any,
>> + * so that bpf_link can be attached
>> + */
>> + if (!(xsk->config.xdp_flags & XDP_FLAGS_UPDATE_IF_NOEXIST)) {
>> + err = bpf_get_link_xdp_id(ctx->ifindex, &prog_id, xsk->config.xdp_flags);
>> + if (err) {
>> + pr_warn("getting XDP prog id failed\n");
>> + return err;
>> + }
>> + if (prog_id) {
>> + err = bpf_set_link_xdp_fd(ctx->ifindex, -1, 0);
>> + if (err < 0) {
>> + pr_warn("detaching XDP prog failed\n");
>> + return err;
>> + }
>> + }
>> }
>>
>> - ctx->prog_fd = prog_fd;
>> + link_fd = bpf_link_create(ctx->prog_fd, xsk->ctx->ifindex, BPF_XDP, &opts);
>> + if (link_fd < 0) {
>> + pr_warn("bpf_link_create failed: %s\n", strerror(errno));
>> + return link_fd;
>> + }
>> +
>
> This can leave the system in a bad state where it unloaded the XDP program
> above, but then failed to create the link. So we should somehow fix that
> if possible or at minimum put a note somewhere so users can't claim they
> shouldn't know this.
>
> Also related, its not good for real systems to let XDP program go missing
> for some period of time. I didn't check but we should make
> XDP_FLAGS_UPDATE_IF_NOEXIST the default if its not already.
>
This is the default for XDP sockets library. The
"bpf_set_link_xdp_fd(...-1)" way is only when a user sets it explicitly.
One could maybe argue that the "force remove" would be out of scope for
AF_XDP; Meaning that if an XDP program is running, attached via netlink,
the AF_XDP library simply cannot remove it. The user would need to rely
on some other mechanism.
Björn
[...]
next prev parent reply other threads:[~2021-02-16 9:21 UTC|newest]
Thread overview: 37+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-02-15 15:46 [PATCH bpf-next 0/3] Introduce bpf_link in libbpf's xsk Maciej Fijalkowski
2021-02-15 15:46 ` [PATCH bpf-next 1/3] libbpf: xsk: use bpf_link Maciej Fijalkowski
2021-02-15 17:07 ` Toke Høiland-Jørgensen
2021-02-15 17:38 ` Björn Töpel
2021-02-15 19:35 ` Toke Høiland-Jørgensen
2021-02-16 2:01 ` Maciej Fijalkowski
2021-02-16 9:15 ` Björn Töpel
2021-02-16 10:27 ` Toke Høiland-Jørgensen
2021-02-16 20:15 ` Maciej Fijalkowski
2021-02-15 20:22 ` John Fastabend
2021-02-15 21:38 ` Toke Høiland-Jørgensen
2021-02-16 0:18 ` John Fastabend
2021-02-16 2:23 ` Maciej Fijalkowski
2021-02-16 9:23 ` Björn Töpel
2021-02-16 10:36 ` Toke Høiland-Jørgensen
2021-02-23 1:15 ` Andrii Nakryiko
2021-02-17 2:23 ` Dan Siemon
2021-02-17 7:16 ` Magnus Karlsson
2021-02-17 7:36 ` Magnus Karlsson
2021-02-16 2:10 ` Maciej Fijalkowski
2021-02-15 20:49 ` John Fastabend
2021-02-16 2:38 ` Maciej Fijalkowski
2021-02-16 18:19 ` John Fastabend
2021-02-16 20:10 ` Maciej Fijalkowski
2021-02-16 9:20 ` Björn Töpel [this message]
2021-02-16 10:39 ` Toke Høiland-Jørgensen
2021-02-16 19:15 ` John Fastabend
2021-02-16 20:50 ` Maciej Fijalkowski
2021-02-16 21:17 ` John Fastabend
2021-02-15 15:46 ` [PATCH bpf-next 2/3] libbpf: clear map_info before each bpf_obj_get_info_by_fd Maciej Fijalkowski
2021-02-15 20:33 ` John Fastabend
2021-02-16 2:42 ` Maciej Fijalkowski
2021-02-15 15:46 ` [PATCH bpf-next 3/3] samples: bpf: do not unload prog within xdpsock Maciej Fijalkowski
2021-02-15 20:24 ` John Fastabend
2021-02-16 9:22 ` Björn Töpel
2021-02-16 14:15 ` Maciej Fijalkowski
2021-02-15 16:07 ` [PATCH bpf-next 0/3] Introduce bpf_link in libbpf's xsk Björn Töpel
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