Skip to contentSkip to conversation

New: tcpi_state field in tcp_info structure reports TCP_CLOSE instead of TCP_TIME_WAIT state

Bugme-new Andrew Morton 2 participants 2 messages Apr 25, 2011 – Jun 7, 2011 1 message not in the archive

Subsystems (2)
Networking Network drivers
lore
Share & tools
lore

Andrew Morton

author
#1 lore raw
In reply to a message not in the archive

(switched to email. Please respond via emailed reply-to-all, not via the bugzilla web interface).

Quoted 38 lines · On Mon, 25 Apr 2011 08:08:36 GMT [email protected] wrote:

https://bugzilla.kernel.org/show_bug.cgi?id=33902

Summary: tcpi_state field in tcp_info structure reports
TCP_CLOSE instead of TCP_TIME_WAIT state
Product: Networking
Version: 2.5
Kernel Version: 2.6.38
Platform: All
OS/Version: Linux
Tree: Mainline
Status: NEW
Severity: normal
Priority: P1
Component: IPV4
AssignedTo: [email protected]
ReportedBy: [email protected]
Regression: No

Setup - TCP connection in ESTABLISHED state. Local socket calls shutdown(SHUT_RDWR). After that peer calls shutdown(SHUT_RDWR).

Local socket should now be in TIME_WAIT state (from specification point of view). And it's indeed in TIME_WAIT (TCP_TIME_WAIT) state if we look at /proc/net/tcp (or netstat -t). However, if one tries to get connection state via tcp_info (getsockopt(TCP_INFO)) the reported state is CLOSED (TCP_CLOSE).

Looks like the problem is in tcp_time_wait() function (net/ipv4/tcp_minisocks.c).
It's called with state=TCP_TIME_WAIT, and sets inet_timewaitk_sock *tw->tw_state field to TCP_TIME_WAIT. That's why the state is reported correctly when looking into /proc. However, at the end it calls tcp_done(sk), which itself calls tcp_set_state(TCP_CLOSE), so sk->sk_state is set to TCP_CLOSE instead of TCP_TIME_WAIT. And it's reported this way via TCP_INFO socket option.

Problem is reproduced on 2.6.26, 2.6.38 and is probably observed on earlier kernels.

maintainer
#2 lore raw

From: Andrew Morton <[email protected]>
Date: Mon, 25 Apr 2011 14:34:21 -0700

Quoted 20 lines
Quoted 17 lines · On Mon, 25 Apr 2011 08:08:36 GMT [email protected] wrote:

Setup - TCP connection in ESTABLISHED state. Local socket calls shutdown(SHUT_RDWR). After that peer calls shutdown(SHUT_RDWR).

Local socket should now be in TIME_WAIT state (from specification point of view). And it's indeed in TIME_WAIT (TCP_TIME_WAIT) state if we look at /proc/net/tcp (or netstat -t). However, if one tries to get connection state via tcp_info (getsockopt(TCP_INFO)) the reported state is CLOSED (TCP_CLOSE).

Looks like the problem is in tcp_time_wait() function (net/ipv4/tcp_minisocks.c).
It's called with state=TCP_TIME_WAIT, and sets inet_timewaitk_sock *tw->tw_state field to TCP_TIME_WAIT. That's why the state is reported correctly when looking into /proc. However, at the end it calls tcp_done(sk), which itself calls tcp_set_state(TCP_CLOSE), so sk->sk_state is set to TCP_CLOSE instead of TCP_TIME_WAIT. And it's reported this way via TCP_INFO socket option.

Quoted 2 lines
Quoted 2 lines

Problem is reproduced on 2.6.26, 2.6.38 and is probably observed on earlier kernels.

As far as the user side of the socket is concerned, it is TCP_CLOSE.

For timewait connections we create a completely seperate light-weight object to manage the network side visible state of the TCP flow. This is not accessible from, and is entirely differently from, the heavy-weight full socket we keep around until the user gives up his final reference.

So I do not see this behavior changing, it would be quite invasive and expensive to make this work as you expect, and only for marginal gain.