[ClusterLabs] Antw: Re: Antw: Re: Antw: Re: [Cluster-devel] DLM connection channel switch take too long time (> 5mins)

[Ulrich Windl]

>>> Guoqing Jiang <gqjiang at suse.com> schrieb am 13.03.2018 um 08:42 in Nachricht
<6f0f512b-c641-72cd-d03b-0a903c84a57f at suse.com>:

> 
> On 03/13/2018 03:09 PM, Ulrich Windl wrote:
>>
>>>>> Guoqing Jiang <gqjiang at suse.com> schrieb am 13.03.2018 um 05:00 in Nachricht
>> <87a8e0e7-63f3-2329-6598-1fa80b1b12d5 at suse.com>:
>>
>>> On 03/08/2018 07:24 PM, Ulrich Windl wrote:
>>>> Hi!
>>>>
>>>> What surprises me most is that a connect(...O_NONBLOCK) actually blocks:
>>>>
>>>> EINPROGRESS
>>>>                 The  socket  is  non-blocking  and the connection cannot be
>>> com-
>>>>                 pleted immediately.
>>>>
>>> Maybe it is because that the socket is created by sock_create_kern, and
>>> O_NONBLOCK flag is not worked  since __sctp_connect has the following
>>> description.
>>>
>>>          /* in-kernel sockets don't generally have a file allocated to them
>>>            * if all they do is call sock_create_kern().
>>>            */
>>>           if (sk->sk_socket->file)
>>>                   f_flags = sk->sk_socket->file->f_flags;
>>>
>>>           timeo = sock_sndtimeo(sk, f_flags & O_NONBLOCK);
>> But O_NONBLOCK is still passed to sock_sndtimeo() (unless the intention was 
> "f_flags & ~O_NONBLOCK").
>>
> 
> If I am not reading wrong, the O_NONBLOCK doesn't have effective above
> since f_flags is still 0.

OK; I didn't look close enough; you are right.

> 
> So, in this case, timeo is set to sk->sk_sndtimeo. In sctp_wait_for_connect
> you also can see nonblock is only work when timeo is set to 0.
> 
>              if (!*timeo_p)
>                          goto do_nonblock;


Another point would be to signal an error for a socket operation with unsupported flags, like O_NONBLOCK here. In the end it's probably better to remove O_NONBLOCK from the call reather than assuming it would have an effect in this case.

The other question (for the kernel developers) is whether the file structure is the best place to pass flags like O_NONBLOCK then.

Regards,
Ulrich