diff options
| author | Octavian Purdila <opurdila@ixiacom.com> | 2009-08-29 00:00:35 -0700 |
|---|---|---|
| committer | David S. Miller <davem@davemloft.net> | 2009-08-29 00:00:35 -0700 |
| commit | 80a1096bac73ce6e98dbbce10cc00a154460bcbd (patch) | |
| tree | d0c520d42e0e72bd2c1b86000a793ea4cf923c5a /net/ipv4 | |
| parent | 80b71b80df14d885f7e50e115c1348398f418759 (diff) | |
tcp: fix premature termination of FIN_WAIT2 time-wait sockets
There is a race condition in the time-wait sockets code that can lead
to premature termination of FIN_WAIT2 and, subsequently, to RST
generation when the FIN,ACK from the peer finally arrives:
Time TCP header
0.000000 30755 > http [SYN] Seq=0 Win=2920 Len=0 MSS=1460 TSV=282912 TSER=0
0.000008 http > 30755 aSYN, ACK] Seq=0 Ack=1 Win=2896 Len=0 MSS=1460 TSV=...
0.136899 HEAD /1b.html?n1Lg=v1 HTTP/1.0 [Packet size limited during capture]
0.136934 HTTP/1.0 200 OK [Packet size limited during capture]
0.136945 http > 30755 [FIN, ACK] Seq=187 Ack=207 Win=2690 Len=0 TSV=270521...
0.136974 30755 > http [ACK] Seq=207 Ack=187 Win=2734 Len=0 TSV=283049 TSER=...
0.177983 30755 > http [ACK] Seq=207 Ack=188 Win=2733 Len=0 TSV=283089 TSER=...
0.238618 30755 > http [FIN, ACK] Seq=207 Ack=188 Win=2733 Len=0 TSV=283151...
0.238625 http > 30755 [RST] Seq=188 Win=0 Len=0
Say twdr->slot = 1 and we are running inet_twdr_hangman and in this
instance inet_twdr_do_twkill_work returns 1. At that point we will
mark slot 1 and schedule inet_twdr_twkill_work. We will also make
twdr->slot = 2.
Next, a connection is closed and tcp_time_wait(TCP_FIN_WAIT2, timeo)
is called which will create a new FIN_WAIT2 time-wait socket and will
place it in the last to be reached slot, i.e. twdr->slot = 1.
At this point say inet_twdr_twkill_work will run which will start
destroying the time-wait sockets in slot 1, including the just added
TCP_FIN_WAIT2 one.
To avoid this issue we increment the slot only if all entries in the
slot have been purged.
This change may delay the slots cleanup by a time-wait death row
period but only if the worker thread didn't had the time to run/purge
the current slot in the next period (6 seconds with default sysctl
settings). However, on such a busy system even without this change we
would probably see delays...
Signed-off-by: Octavian Purdila <opurdila@ixiacom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'net/ipv4')
| -rw-r--r-- | net/ipv4/inet_timewait_sock.c | 2 |
1 files changed, 1 insertions, 1 deletions
diff --git a/net/ipv4/inet_timewait_sock.c b/net/ipv4/inet_timewait_sock.c index 61283f928825..13f0781f35cd 100644 --- a/net/ipv4/inet_timewait_sock.c +++ b/net/ipv4/inet_timewait_sock.c @@ -218,8 +218,8 @@ void inet_twdr_hangman(unsigned long data) /* We purged the entire slot, anything left? */ if (twdr->tw_count) need_timer = 1; + twdr->slot = ((twdr->slot + 1) & (INET_TWDR_TWKILL_SLOTS - 1)); } - twdr->slot = ((twdr->slot + 1) & (INET_TWDR_TWKILL_SLOTS - 1)); if (need_timer) mod_timer(&twdr->tw_timer, jiffies + twdr->period); out: |