dovecot - Dec 2008 - Dovecot imap processes pinning CPU

In recent days, dovecot's "imap" processes keep getting stuck. 
Each
time I check my server (running dovecot 1.1.7) there's a bunch of
"imap"
processes (sometimes 2 of them, sometimes 4, sometimes 6) that are using 
all of the box's CPU.

And worse, there's no way to kill the processes either (neither kill -15 
or kill -9 works), which means that I wind up having to reboot the box 
every time this happens.  REALLY irritating.

I don't normally even *see* the imap processes in htop, as I think 
they're pretty short lived.  And I'm not sure what they're looping 
trying to do.  My debugging skills on Linux are a bit weak, and so I 
don't know how to look at the process and see what it's doing.

Also, not sure what's changed on my system to cause this, as this is
definitely a recent problem.  Maybe the upgrade to Thunderbird 2.0.0.18
(since I usually use T'Bird to access my email).  I don't seem to run 
into this problem when I use Squirrelmail.

Anyone have any idea what the problem might be?  Or, if not, then 
suggestions on how I might be able to debug the situation myself?

TIA,

DR

On Dec 13, 2008, at 3:40 AM, David Rosenstrauch wrote:
> In recent days, dovecot's "imap" processes keep getting
stuck.  Each
> time I check my server (running dovecot 1.1.7) there's a bunch of  
> "imap" processes (sometimes 2 of them, sometimes 4, sometimes 6)
> that are using all of the box's CPU.
>
> And worse, there's no way to kill the processes either (neither kill  
> -15 or kill -9 works), which means that I wind up having to reboot  
> the box every time this happens.  REALLY irritating.
I wonder what's going on. You're the 3rd person who has started a  
thread about this within a few days. See the "unkillable imap  
process(es) with high CPU-usage" thread that's going on, with the  
exact same issue..
http://dovecot.org/list/dovecot/2008-December/035662.html
> I don't normally even *see* the imap processes in htop, as I think  
> they're pretty short lived.
Depends on the clients, but many clients keep IMAP connections open  
for a long time, so the imap processes should be long living.

What distribution and kernel version are you using?

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On Sat, December 13, 2008 12:28 am, Timo Sirainen wrote:
> On Dec 13, 2008, at 3:40 AM, David Rosenstrauch wrote:
>
>> In recent days, dovecot's "imap" processes keep getting
stuck.  Each
>> time I check my server (running dovecot 1.1.7) there's a bunch of
>> "imap" processes (sometimes 2 of them, sometimes 4, sometimes
6)
>> that are using all of the box's CPU.
>
> I wonder what's going on. You're the 3rd person who has started a
> thread about this within a few days. See the "unkillable imap
> process(es) with high CPU-usage" thread that's going on, with the
> exact same issue..
> http://dovecot.org/list/dovecot/2008-December/035662.html

Wow.  Yeah, *some*thing's changed recently to cause this.  If I had to
guess, I'd say it's a recent Thunderbird upgrade that's triggering
it, as
it's been 2-3 weeks since my last dovecot upgrade.

I'll take a look at that thread.

> What distribution and kernel version are you using?
Arch Linux, kernel 2.6.27.8

Thanks,

DR

Just saw this thread on 
http://dovecot.org/list/dovecot/2008-December/035707.html and I hope 
that this email gets through (I'm not subscribed).

The described behaviour seems to be a bug in Linux 2.6.27.8: 
http://lkml.indiana.edu/hypermail/linux/kernel/0812.1/00006.html

This fix seems to work for me: 
http://lkml.indiana.edu/hypermail/linux/kernel/0812.1/00998.html

It is not fixed in 2.6.27.9, but will be fixed in 2.6.27.10 according to 
Greg KH: http://lkml.org/lkml/2008/12/14/162

Hope that helps
Steffen

Steffen Weber wrote:
> Just saw this thread on
> This fix seems to work for me:
> http://lkml.indiana.edu/hypermail/linux/kernel/0812.1/00998.html
That fixed it for me as well. You can get the patch from gitweb at
(formatting is a bit nicer for patching):

http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=711a49a07f84f914aac26a52143f6e7526571143
> It is not fixed in 2.6.27.9, but will be fixed in 2.6.27.10 according to
> Greg KH: http://lkml.org/lkml/2008/12/14/162
Good, I guess we just picked the wrong time to update our mail server to
the latest stable kernel.

> That fixed it for me as well. You can get the patch from gitweb at
> (formatting is a bit nicer for patching):
>
>
http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=711a49a07f84f914aac26a52143f6e7526571143
>
>> It is not fixed in 2.6.27.9, but will be fixed in 2.6.27.10 according
to
>> Greg KH: http://lkml.org/lkml/2008/12/14/162
>
> Good, I guess we just picked the wrong time to update our mail server to
> the latest stable kernel.
That patch seems to have fixed it for me too