Hey Nick and Florian,

Starting in 4.14 iscsi logins will fail around 50% of the time.

I git bisected the issue down to this commit:

commit e7942d0633c47c791ece6afa038be9cf977226de
Author: Florian Westphal <fw@strlen.de>
Date:   Sun Jul 30 03:57:18 2017 +0200

    tcp: remove prequeue support

Nick, attached is the iscsi target log info when the login fails.

You can see at:

Dec 13 17:55:01 rhel73n1 kernel: Got Login Command, Flags 0x81, ITT:
0x00000000, CmdSN: 0x00000000, ExpStatSN: 0xf86dc69b, CID: 0, Length: 65

we have got a login command and we seem to then go into
iscsit_do_rx_data -> sock_recvmsg

We seem to get stuck in there though, because we stay blocked until:

Dec 13 17:55:01 rhel73n1 kernel: Entering iscsi_target_sk_data_ready:
conn: ffff88b35cbb3000
Dec 13 17:55:01 rhel73n1 kernel: Got LOGIN_FLAGS_READ_ACTIVE=1, conn:
ffff88b35cbb3000 >>>>

where initiator side timeout fires 15 seconds later and it disconnects
the tcp connection, and we eventually break out of the recvmsg call:

Dec 13 17:55:16 rhel73n1 kernel: Entering iscsi_target_sk_state_change
Dec 13 17:55:16 rhel73n1 kernel: __iscsi_target_sk_check_close:
TCP_CLOSE_WAIT|TCP_CLOSE,returning FALSE

....

Dec 13 17:55:16 rhel73n1 kernel: rx_loop: 68, total_rx: 68, data: 68
Dec 13 17:55:16 rhel73n1 kernel: iscsi_target_do_login_rx after
rx_login_io, ffff88b35cbb3000, kworker/2:2:1829

Is the iscsi target doing something incorrect in its use of
sk_data_ready and sock_recvmsg or is the tcp patch at fault?