HEADS UP: tcp wrongly persist timer detection
sepherosa at gmail.com
Tue Dec 21 01:33:41 PST 2010
HEAD users only.
It could panic your system upon TCP activities, so please backup your
working kernel :). If the panic happens, please send us the link to
the core dumps.
Thank you for your help in advance.
---------- Forwarded message ----------
From: Sepherosa Ziehau <sephe at crater.dragonflybsd.org>
Date: Tue, Dec 21, 2010 at 5:11 PM
Subject: git: tcp: Don't allow persist timer if TCP connection is not
Author: Sepherosa Ziehau <sephe at dragonflybsd.org>
Date: Tue Dec 21 16:26:34 2010 +0800
tcp: Don't allow persist timer if TCP connection is not established yet
This probably could move the un-updated snd_nxt panic earlier.
The dump of the panic in http://bugs.dragonflybsd.org/issue1939 shows
- snd_nxt is less than snd_una
- A persist timer was fired (frame 16, tp->tt_msg->tt_prev_tasks).
- The TCP segment triggered the panic has SYN|ACK (frame 17, th->th_flags).
This TCP segment is considered as valid (frame 17, list), so tp->t_state
This explains why snd_nxt is less than snd_una:
If tcp_output() is called by persist timer, then the persist timer is
active and the "forced" is turned on, this causes the snd_nxt not updated
MISSING CHIAN IN THE LINK:
How is the persist timer got set in the SYN_SENT in the first place?
Hope the new panic could lift the veil...
Summary of changes:
sys/netinet/tcp_output.c | 5 ++++-
1 files changed, 4 insertions(+), 1 deletions(-)
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