Subject: Fwd: Kernel Oops in __inet_twsk_kill()

From: Daniel Borkmann <[email-masked]>
Date: Wed, 05 Nov 2014 17:00:52 +0100

[ moving to netdev ]

-------- Original Message --------
Subject: Kernel Oops in __inet_twsk_kill()
Date: Tue, 4 Nov 2014 23:47:18 +0000
From: Charley (Hao Chuan) Chu <[email-masked]>
To: [email-masked] <[email-masked]>

We have situation on our system. It brings the network interface up and down every
a few seconds. Eventually, it brings down the system - the kernel crashed due to BUG
on in __inet_twsk_kill(). The debug message show following call flow.

1) time-wait socket is created by tcp_time_wait() when the socket gets into "TIME_WAIT" state.
     inet_twsk_alloc()               - refcnt= 0
     inet_twsk_hashdance()  - refcnt = 3
     inet_twsk_schedule()      - refcnt = 4
     inet_twsk_put()                 - refcnt = 3
2) tcp_v4_timewait_ack() is called when sync is received
     inet_twsk_put()                  - refcnt= 2      <== where we thing the problem is
     occasionally, second sync is received, so the inet_twsk_put is called twice - refcnt = 1
3) twdr_do_twkill_work() is called when timed out
     call __inet_twsk_kill - BUG_ON!!! as refcnt=2 (supposed to be 3).
     call inet_twsk_put()

In a normal case, the callflow only has step 1 and step 3.  Our understanding is
the time-wait socket has three references - ehash, bhash and timer death row. In
step 2, none of them are touched. Can anyone here explain to us why the inet_twsk_put()
is called in tcp_v4_timewait_ack()?

our system has 3.14 kernel.

Any help would be highly appreciated.

Charley Chu