From: Karsten Graul <kgraul@linux.ibm.com>
To: Guangguan Wang <guangguan.wang@linux.alibaba.com>,
davem@davemloft.net, kuba@kernel.org, pabeni@redhat.com
Cc: linux-s390@vger.kernel.org, netdev@vger.kernel.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH net-next v2] net/smc: align the connect behaviour with TCP
Date: Tue, 24 May 2022 14:04:06 +0200 [thread overview]
Message-ID: <26d43c65-1f23-5b83-6377-3327854387c4@linux.ibm.com> (raw)
In-Reply-To: <45a19f8b-1b64-3459-c28c-aebab4fd8f1e@linux.alibaba.com>
On 24/05/2022 04:59, Guangguan Wang wrote:
>
>
> On 2022/5/23 20:24, Karsten Graul wrote:
>> On 13/05/2022 04:24, Guangguan Wang wrote:
>>> Connect with O_NONBLOCK will not be completed immediately
>>> and returns -EINPROGRESS. It is possible to use selector/poll
>>> for completion by selecting the socket for writing. After select
>>> indicates writability, a second connect function call will return
>>> 0 to indicate connected successfully as TCP does, but smc returns
>>> -EISCONN. Use socket state for smc to indicate connect state, which
>>> can help smc aligning the connect behaviour with TCP.
>>>
>>> Signed-off-by: Guangguan Wang <guangguan.wang@linux.alibaba.com>
>>> Acked-by: Karsten Graul <kgraul@linux.ibm.com>
>>> ---
>>> net/smc/af_smc.c | 50 ++++++++++++++++++++++++++++++++++++++++++++----
>>> 1 file changed, 46 insertions(+), 4 deletions(-)
>>>
>>> diff --git a/net/smc/af_smc.c b/net/smc/af_smc.c
>>> index fce16b9d6e1a..5f70642a8044 100644
>>> --- a/net/smc/af_smc.c
>>> +++ b/net/smc/af_smc.c
>>> @@ -1544,9 +1544,29 @@ static int smc_connect(struct socket *sock, struct sockaddr *addr,
>>> goto out_err;
>>>
>>> lock_sock(sk);
>>> + switch (sock->state) {
>>> + default:
>>> + rc = -EINVAL;
>>> + goto out;
>>> + case SS_CONNECTED:
>>> + rc = sk->sk_state == SMC_ACTIVE ? -EISCONN : -EINVAL;
>>> + goto out;
>>> + case SS_CONNECTING:
>>> + if (sk->sk_state == SMC_ACTIVE)
>>> + goto connected;
>>
>> I stumbled over this when thinking about the fallback processing. If for whatever reason
>> fallback==true during smc_connect(), the "if (smc->use_fallback)" below would set sock->state
>> to e.g. SS_CONNECTED. But in the fallback case sk_state keeps SMC_INIT. So during the next call
>> the SS_CONNECTING case above would break because sk_state in NOT SMC_ACTIVE, and we would end
>> up calling kernel_connect() again. Which seems to be no problem when kernel_connect() returns
>> -EISCONN and we return this to the caller. But is this how it should work, or does it work by chance?
>>
>
> Since the sk_state keeps SMC_INIT and does not correctly indicate the state of clcsock, it should end
> up calling kernel_connect() again to get the actual connection state of clcsock.
>
> And I'm sorry there is a problem that if sock->state==SS_CONNECTED and sk_state==SMC_INIT, further call
> of smc_connect will return -EINVAL where -EISCONN is preferred.
> The steps to reproduce:
> 1)switch fallback before connect, such as setsockopt TCP_FASTOPEN
> 2)connect with noblocking and returns -EINPROGRESS. (sock->state changes to SS_CONNECTING)
> 3) end up calling connect with noblocking again and returns 0. (kernel_connect() returns 0 and sock->state changes to
> SS_CONNECTED but sk->sk_state stays SMC_INIT)
> 4) call connect again, maybe by mistake, will return -EINVAL, but -EISCONN is preferred.
>
> What do you think about if we synchronize the sk_state to SMC_ACTIVE instead of keeping SMC_INIT when clcsock
> connected successfully in fallback case described above.
>
> ...
I start thinking that the fix in 86434744 introduced a problem. Before that fix a connect with
fallback always reached __smc_connect() and on top of that function in case of fallback
smc_connect_fallback() is called, which itself sets sk_state to SMC_ACTIVE.
86434744 removed that code path and I wonder what it actually fixed, because at this time the
fallback check in __smc_connect() was already present.
Without that "goto out;" the state would be set correctly in smc_connect_fallback(), and the
socket close processing would work as expected.
next prev parent reply other threads:[~2022-05-24 12:04 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-05-13 2:24 [PATCH net-next v2] net/smc: align the connect behaviour with TCP Guangguan Wang
2022-05-16 9:50 ` patchwork-bot+netdevbpf
2022-05-23 12:24 ` Karsten Graul
2022-05-24 2:59 ` Guangguan Wang
2022-05-24 12:04 ` Karsten Graul [this message]
2022-05-24 12:57 ` liuyacan
2022-05-24 13:05 ` Karsten Graul
2022-06-29 20:29 ` Wenjia Zhang
[not found] ` <8a15e288-4534-501c-8b3d-c235ae93238f@linux.ibm.com>
2022-06-30 14:29 ` Guangguan Wang
2022-06-30 20:16 ` Wenjia Zhang
2022-07-01 2:03 ` Guangguan Wang
2022-07-01 12:45 ` Wenjia Zhang
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=26d43c65-1f23-5b83-6377-3327854387c4@linux.ibm.com \
--to=kgraul@linux.ibm.com \
--cc=davem@davemloft.net \
--cc=guangguan.wang@linux.alibaba.com \
--cc=kuba@kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-s390@vger.kernel.org \
--cc=netdev@vger.kernel.org \
--cc=pabeni@redhat.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).