path: root/net/ipv4/inet_timewait_sock.c
diff options
authorOctavian Purdila <opurdila@ixiacom.com>2009-08-29 00:00:35 -0700
committerDavid S. Miller <davem@davemloft.net>2009-08-29 00:00:35 -0700
commit80a1096bac73ce6e98dbbce10cc00a154460bcbd (patch)
treed0c520d42e0e72bd2c1b86000a793ea4cf923c5a /net/ipv4/inet_timewait_sock.c
parentfib_trie: resize rework (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/inet_timewait_sock.c')
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);