Cyrus 2.3.8 imapd process periodically sticks at 100% CPU

[Mark Cave-Ayland]

Hi there,

I'm experiencing a problem with Cyrus 2.3.8 interacting with an Outlook 
client and was hoping this would be the right place to get some advice.

What happens is that periodically (maybe around once a month?) we have 
one particular user who contacts us complaining that they are unable 
access their mailbox. Generally we always find the same thing: there is 
an imapd process accessing his seen DB which is running at 100% CPU. 
Once this process is killed then things go back to normal and the user 
can log in.

The latest report we had of this problem happening again was this 
morning, and fortunately I was in a position to attack it with gdb and a 
file of debug symbols. This showed that the process in question was 
getting stuck in a loop in index_expungeuidlist(). I've uploaded the 
transcript of my gdb session to 
http://pastebin.siriusit.co.uk/cyrus-imapd-gdb.txt for people who are 
familiar with cyrus internals.

The short story appears to be that newseenuids (new) points to an empty 
string ('\0') and so the code gets stuck because of the following at 
line 532 of imap/index.c in index_checkseen():

oldseen = (*old == ':');

Since *old is an empty string, oldseen will always be 0, and so the 
while() loop never exits. Unfortunately this is the first time I've ever 
looked at cyrus internals, so am not really sure what the seen list 
should look like normally.

The confusing thing is that we have been using these packages for 
several clients and this is the *only* particular server and the *only* 
user on this server experiencing this problem. The one thing we have 
noticed is that this particular user has a larger mailbox compared to 
the other users (~1GB) but then it doesn't seem so large as if it would 
cause any problems.

Finally, one more thing to add is that we have already gone through the 
steps of rebuilding the seen DB skiplist using the skiplist.py script 
several times when this has happened in the past, and it has made no 
difference.


Many thanks,

Mark.

-- 
Mark Cave-Ayland
Sirius Corporation - The Open Source Experts
http://www.siriusit.co.uk
T: +44 870 608 0063