Re: [PATCH] cifs: do not fail __smb_send_rqst if non-fatal signals are pending

[Pavel Shilovsky <piastryyy@gmail.com>]

пн, 25 янв. 2021 г. в 08:39, Shyam Prasad N <nspmangalore@gmail.com>:
>
> Hi Pavel,
>
> Sorry for the late review on this. A few minor comments on __smb_send_rqst():
>
>     if ((total_len > 0) && (total_len != send_length)) { <<<< what's
> special about total_len == 0? I'm guessing send_length will also be 0
> in such a case.


Should be. I don't think there should be a case of sending zero-length SMBs.


>         cifs_dbg(FYI, "partial send (wanted=%u sent=%zu): terminating
> session\n",
>              send_length, total_len);
>         /*
>          * If we have only sent part of an SMB then the next SMB could
>          * be taken as the remainder of this one. We need to kill the
>          * socket so the server throws away the partial SMB
>          */
>         server->tcpStatus = CifsNeedReconnect;
>         trace_smb3_partial_send_reconnect(server->CurrentMid,
>                           server->hostname);
>     }
>
> I'm not an expert on kernel socket programming, but if total_len !=
> sent_length, shouldn't we iterate retrying till they become equal (or
> abort if there's no progress)?

Given that this is a blocking send, total_len != send_length may
happen for several reasons: tcp buffers are full and signal is pending
or a connection is reset or closed.

> I see that we cork the connection before send, and I guess it's
> unlikely why only a partial write will occur (Since these are just
> in-memory writes).

For the reasons mentioned above partial send may occur any time.

> But what is the reason for reconnecting on partial writes?

partially sent SMBs would mean corrupted packets on the server and the
server will close the connection anyway.

>
> smbd_done:
>     if (rc < 0 && rc != -EINTR)   <<<<< Not very critical, but
> shouldn't we also check for rc != -ERESTARTSYS?

It doesn't seem like ERESTARTSYS may occur above but not 100% sure
here - needs investigations.


>         cifs_server_dbg(VFS, "Error %d sending data on socket to server\n",
>              rc);
>     else if (rc > 0)
>         rc = 0;
>
>     return rc;
> }
>
> Regards,
> Shyam



--
Best regards,
Pavel Shilovsky