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From: Jakub Sitnicki <jakub@cloudflare.com>
To: Martin Lau <kafai@fb.com>
Cc: John Fastabend <john.fastabend@gmail.com>,
	Alexei Starovoitov <alexei.starovoitov@gmail.com>,
	"bpf\@vger.kernel.org" <bpf@vger.kernel.org>,
	"netdev\@vger.kernel.org" <netdev@vger.kernel.org>,
	"kernel-team\@cloudflare.com" <kernel-team@cloudflare.com>
Subject: Re: [PATCH bpf-next 5/8] bpf: Allow selecting reuseport socket from a SOCKMAP
Date: Wed, 27 Nov 2019 22:34:10 +0100	[thread overview]
Message-ID: <87blsxngvh.fsf@cloudflare.com> (raw)
In-Reply-To: <20191126190301.quwvjihpdzfjhdbe@kafai-mbp.dhcp.thefacebook.com>

On Tue, Nov 26, 2019 at 08:03 PM CET, Martin Lau wrote:
> On Tue, Nov 26, 2019 at 03:30:57PM +0100, Jakub Sitnicki wrote:
>> On Mon, Nov 25, 2019 at 11:07 PM CET, Martin Lau wrote:
>> > On Mon, Nov 25, 2019 at 11:40:41AM +0100, Jakub Sitnicki wrote:

[...]

>> I agree, it's not obvious. When I first saw this check in
>> reuseport_array_update_check it got me puzzled too. I should have added
>> an explanatory comment there.
>>
>> Thing is we're not matching on just TCP_LISTEN. REUSEPORT_SOCKARRAY
>> allows selecting a connected UDP socket as a target as well. It takes
>> some effort to set up but it's possible even if obscure.
> How about this instead:
> if (!reuse)
>  	/* reuseport_array only has sk that has non NULL sk_reuseport_cb.
> 	 * The only (!reuse) case here is, the sk has already been removed from
> 	 * reuseport_array, so treat it as -ENOENT.
> 	 *
> 	 * Other maps (e.g. sock_map) do not provide this guarantee and the sk may
> 	 * never be in the reuseport to begin with.
> 	 */
> 	return map->map_type == BPF_MAP_TYPE_REUSEPORT_SOCKARRAY ? -ENOENT : -EINVAL;

Right, apart from established TCP sockets we must not select a listening
socket that's not in a reuseport group either. This covers both
cases. Clever. Thanks for the suggestion.

>
>>
>> > Note that the SOCK_RCU_FREE check at the 'slow-path'
>> > reuseport_array_update_check() is because reuseport_array does depend on
>> > call_rcu(&sk->sk_rcu,...) to work, e.g. the reuseport_array
>> > does not hold the sk_refcnt.
>>
>> Oh, so it's not only about socket state like I thought.
>>
>> This raises the question - does REUSEPORT_SOCKARRAY allow storing
>> connected UDP sockets by design or is it a happy accident? It doesn't
>> seem particularly useful.
> Not by design/accident on the REUSEPORT_SOCKARRAY side ;)
>
> The intention of REUSEPORT_SOCKARRAY is to allow sk that can be added to
> reuse->socks[].

Ah, makes sense. REUSEPORT_SOCKARRAY had to mimic reuseport groups.

-Jakub

  reply	other threads:[~2019-11-27 21:34 UTC|newest]

Thread overview: 39+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-11-23 11:07 [PATCH bpf-next 0/8] Extend SOCKMAP to store listening sockets Jakub Sitnicki
2019-11-23 11:07 ` [PATCH bpf-next 1/8] bpf, sockmap: Return socket cookie on lookup from syscall Jakub Sitnicki
2019-11-24  5:32   ` John Fastabend
2019-11-23 11:07 ` [PATCH bpf-next 2/8] bpf, sockmap: Let all kernel-land lookup values in SOCKMAP Jakub Sitnicki
2019-11-24  5:35   ` John Fastabend
2019-11-23 11:07 ` [PATCH bpf-next 3/8] bpf, sockmap: Allow inserting listening TCP sockets into SOCKMAP Jakub Sitnicki
2019-11-24  5:38   ` John Fastabend
2019-11-23 11:07 ` [PATCH bpf-next 4/8] bpf, sockmap: Don't let child socket inherit psock or its ops on copy Jakub Sitnicki
2019-11-24  5:56   ` John Fastabend
2019-11-25 22:38   ` Martin Lau
2019-11-26 15:54     ` Jakub Sitnicki
2019-11-26 17:16       ` Martin Lau
2019-11-26 18:36         ` Jakub Sitnicki
     [not found]           ` <87sglsfdda.fsf@cloudflare.com>
2019-12-11 17:20             ` Martin Lau
2019-12-12 11:27               ` Jakub Sitnicki
2019-12-12 19:23                 ` Martin Lau
2019-12-17 15:06                   ` Jakub Sitnicki
2019-11-26 18:43         ` John Fastabend
2019-11-27 22:18           ` Jakub Sitnicki
2019-11-23 11:07 ` [PATCH bpf-next 5/8] bpf: Allow selecting reuseport socket from a SOCKMAP Jakub Sitnicki
2019-11-24  5:57   ` John Fastabend
2019-11-25  1:24   ` Alexei Starovoitov
2019-11-25  4:17     ` John Fastabend
2019-11-25 10:40       ` Jakub Sitnicki
2019-11-25 22:07         ` Martin Lau
2019-11-26 14:30           ` Jakub Sitnicki
2019-11-26 19:03             ` Martin Lau
2019-11-27 21:34               ` Jakub Sitnicki [this message]
2019-11-23 11:07 ` [PATCH bpf-next 6/8] libbpf: Recognize SK_REUSEPORT programs from section name Jakub Sitnicki
2019-11-24  5:57   ` John Fastabend
2019-11-23 11:07 ` [PATCH bpf-next 7/8] selftests/bpf: Extend SK_REUSEPORT tests to cover SOCKMAP Jakub Sitnicki
2019-11-24  6:00   ` John Fastabend
2019-11-25 22:30   ` Martin Lau
2019-11-26 14:32     ` Jakub Sitnicki
2019-12-12 10:30     ` Jakub Sitnicki
2019-11-23 11:07 ` [PATCH bpf-next 8/8] selftests/bpf: Tests for SOCKMAP holding listening sockets Jakub Sitnicki
2019-11-24  6:04   ` John Fastabend
2019-11-24  6:10 ` [PATCH bpf-next 0/8] Extend SOCKMAP to store " John Fastabend
2019-11-25  9:22   ` Jakub Sitnicki

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