[Dovecot] unkillable imap process(es) with high CPU-usage

[Arno Wald]

Hello,

I am having a problem with my dovecot-daemon. It is forking one or more
(I saw up to perhaps 8 of them) imap processes under my user name. These
processes are consuming a lot of CPU time and are not killable:

>  PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND
> 8616 arno      20   0  2900 1600 1204 R   98  0.2   1196:38 imap

Stopping dovecot does not quit these processes. Killing them (even "kill
-9" as root) is not possible. The only solution to get rid of them is to
reboot.

I have found a mailing list post of one who seemed to have the same
problem. He solved it by upgrading to version 1.1. But in my case this
did not help.

Is this a known problem? What could I check or do?

My system:
very up to date debian/sid (sidux)
kernel 2.6.27-8.slh.1-sidux-686
CPU: Intel(R) Core(TM)2 CPU    4300  @ 1.80GHz
Filesystem: ext3fs

tried dovecot from sid: 1:1.0.15-2.3
tried dovecot from experimental: 1:1.1.2-3

My dovecot.conf is the original debian configuration with only one line
changed into:
  protocols = imaps

# dovecot -n
# 1.1.2: /etc/dovecot/dovecot.conf
log_timestamp: %Y-%m-%d %H:%M:%S
protocols: imaps
login_dir: /var/run/dovecot/login
login_executable: /usr/lib/dovecot/imap-login
mail_privileged_group: mail
auth default:
  passdb:
    driver: pam
  userdb:
    driver: passwd

I am using dovecot locally on my system with me as the only user. As
client I am using thunderbird alias icedove 2.0.0.17-1. Icedove
retrieves the Mails from another imap server and sorts them into
Maildir-folders in dovecot. I do not know when the imap-process are
going mad. It happens after the system (and the mail-client) is up for a
while.

Do you need more information?

Thanks,
Arno