From: "Toke Høiland-Jørgensen" <toke@redhat.com>
To: "Björn Töpel" <bjorn.topel@gmail.com>,
ast@kernel.org, daniel@iogearbox.net, netdev@vger.kernel.org,
bpf@vger.kernel.org
Cc: "Björn Töpel" <bjorn.topel@intel.com>,
magnus.karlsson@intel.com, maciej.fijalkowski@intel.com,
kuba@kernel.org, jonathan.lemon@gmail.com, maximmi@nvidia.com,
davem@davemloft.net, hawk@kernel.org, john.fastabend@gmail.com,
ciara.loftus@intel.com, weqaar.a.janjua@intel.com
Subject: Re: [PATCH bpf-next v2 1/8] xdp: restructure redirect actions
Date: Wed, 20 Jan 2021 13:44:24 +0100 [thread overview]
Message-ID: <87bldjeq1j.fsf@toke.dk> (raw)
In-Reply-To: <20210119155013.154808-2-bjorn.topel@gmail.com>
Björn Töpel <bjorn.topel@gmail.com> writes:
> From: Björn Töpel <bjorn.topel@intel.com>
>
> The XDP_REDIRECT implementations for maps and non-maps are fairly
> similar, but obviously need to take different code paths depending on
> if the target is using a map or not. Today, the redirect targets for
> XDP either uses a map, or is based on ifindex.
>
> Future commits will introduce yet another redirect target via the a
> new helper, bpf_redirect_xsk(). To pave the way for that, we introduce
> an explicit redirect type to bpf_redirect_info. This makes the code
> easier to follow, and makes it easier to add new redirect targets.
>
> Further, using an explicit type in bpf_redirect_info has a slight
> positive performance impact by avoiding a pointer indirection for the
> map type lookup, and instead use the hot cacheline for
> bpf_redirect_info.
>
> The bpf_redirect_info flags member is not used by XDP, and not
> read/written any more. The map member is only written to when
> required/used, and not unconditionally.
I like the simplification. However, the handling of map clearing becomes
a bit murky with this change:
You're not changing anything in bpf_clear_redirect_map(), and you're
removing most of the reads and writes of ri->map. Instead,
bpf_xdp_redirect_map() will store the bpf_dtab_netdev pointer in
ri->tgt_value, which xdp_do_redirect() will just read and use without
checking. But if the map element (or the entire map) has been freed in
the meantime that will be a dangling pointer. I *think* the RCU callback
in dev_map_delete_elem() and the rcu_barrier() in dev_map_free()
protects against this, but that is by no means obvious. So confirming
this, and explaining it in a comment would be good.
Also, as far as I can tell after this, ri->map is only used for the
tracepoint. So how about just storing the map ID and getting rid of the
READ/WRITE_ONCE() entirely?
(Oh, and related to this I think this patch set will conflict with
Hangbin's multi-redirect series, so maybe you two ought to coordinate? :))
-Toke
next prev parent reply other threads:[~2021-01-20 20:12 UTC|newest]
Thread overview: 45+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-01-19 15:50 [PATCH bpf-next v2 0/8] Introduce bpf_redirect_xsk() helper Björn Töpel
2021-01-19 15:50 ` [PATCH bpf-next v2 1/8] xdp: restructure redirect actions Björn Töpel
2021-01-20 12:44 ` Toke Høiland-Jørgensen [this message]
2021-01-20 13:40 ` Björn Töpel
2021-01-20 14:52 ` Toke Høiland-Jørgensen
2021-01-20 15:49 ` Björn Töpel
2021-01-20 16:30 ` Toke Høiland-Jørgensen
2021-01-20 17:26 ` Björn Töpel
2021-01-19 15:50 ` [PATCH bpf-next v2 2/8] xsk: remove explicit_free parameter from __xsk_rcv() Björn Töpel
2021-01-19 15:50 ` [PATCH bpf-next v2 3/8] xsk: fold xp_assign_dev and __xp_assign_dev Björn Töpel
2021-01-19 15:50 ` [PATCH bpf-next v2 4/8] xsk: register XDP sockets at bind(), and add new AF_XDP BPF helper Björn Töpel
2021-01-20 8:25 ` kernel test robot
2021-01-20 8:41 ` Björn Töpel
2021-01-20 8:50 ` kernel test robot
2021-01-20 12:50 ` Toke Høiland-Jørgensen
2021-01-20 13:25 ` Björn Töpel
2021-01-20 14:54 ` Toke Høiland-Jørgensen
2021-01-20 15:18 ` Björn Töpel
2021-01-20 17:29 ` Toke Høiland-Jørgensen
2021-01-20 18:22 ` Björn Töpel
2021-01-20 20:26 ` Toke Høiland-Jørgensen
2021-01-20 21:15 ` Alexei Starovoitov
2021-01-21 8:18 ` Björn Töpel
2021-01-19 15:50 ` [PATCH bpf-next v2 5/8] libbpf, xsk: select AF_XDP BPF program based on kernel version Björn Töpel
2021-01-20 12:52 ` Toke Høiland-Jørgensen
2021-01-20 13:25 ` Björn Töpel
2021-01-20 14:49 ` Björn Töpel
2021-01-20 15:11 ` Toke Høiland-Jørgensen
2021-01-20 15:27 ` Björn Töpel
2021-01-20 17:30 ` Toke Høiland-Jørgensen
2021-01-20 18:25 ` Alexei Starovoitov
2021-01-20 18:30 ` Björn Töpel
2021-01-20 14:56 ` Toke Høiland-Jørgensen
2021-01-19 15:50 ` [PATCH bpf-next v2 6/8] libbpf, xsk: select bpf_redirect_xsk(), if supported Björn Töpel
2021-01-19 15:50 ` [PATCH bpf-next v2 7/8] selftest/bpf: add XDP socket tests for bpf_redirect_{xsk, map}() Björn Töpel
2021-01-21 7:39 ` Andrii Nakryiko
2021-01-21 12:31 ` Björn Töpel
2021-01-19 15:50 ` [PATCH bpf-next v2 8/8] selftest/bpf: remove a lot of ifobject casting in xdpxceiver Björn Töpel
2021-01-20 13:15 ` [PATCH bpf-next v2 0/8] Introduce bpf_redirect_xsk() helper Maxim Mikityanskiy
2021-01-20 13:27 ` Björn Töpel
2021-01-20 15:57 ` Jesper Dangaard Brouer
2021-01-20 16:19 ` Maciej Fijalkowski
2021-01-21 17:01 ` Jesper Dangaard Brouer
2021-01-22 8:59 ` Magnus Karlsson
2021-01-22 9:45 ` Maciej Fijalkowski
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