dovecot - Mar 2016 - ETOOMANYREFS related errors

Hi,

I'm starting to see, on a pretty standard Debian Jessie installation, some
error messages that are apparently related to the ETOOMANYREFS errno.

Firstly, the mail log shows this:
dovecot: pop3-login: Error: fd_send(pop3, 18) failed: Too many references:
cannot splice

And then the login process fails:
dovecot: pop3-login: Internal login failure (pid=34388 id=1) (internal
failure, 1 successful auths): user=<username>, method=PLAIN, rip=rip,
lip=lip, session=<session>

Is this something that Dovecot should be able to handle, or is it strictly
Debian/libc/MySillyMistake related?

#uname -a
Linux server 3.16.0-4-amd64 #1 SMP Debian 3.16.7-ckt20-1+deb8u3
(2016-01-17) x86_64 GNU/Linux

#dovecot --version
2.2.13

#dpkg -l | grep -E 'dovecot-core|libc6|linux-image'
ii  dovecot-core                   1:2.2.13-12~deb8u1        amd64
ii  libc6:amd64                    2.19-18+deb8u3            amd64
ii  libc6-i386                     2.19-18+deb8u3            amd64
ii  linux-image-3.16.0-4-amd64     3.16.7-ckt20-1+deb8u3     amd64

Best Regards,
Luis

On 11 Mar 2016, at 03:48, Luis Ugalde <forondarena at gmail.com>
wrote:
> 
> Hi,
> 
> I'm starting to see, on a pretty standard Debian Jessie installation,
some
> error messages that are apparently related to the ETOOMANYREFS errno.
> 
> Firstly, the mail log shows this:
> dovecot: pop3-login: Error: fd_send(pop3, 18) failed: Too many references:
> cannot splice
Apparently because Linux thinks the same fd has been passed around recursively
too many times: http://lkml.iu.edu/hypermail/linux/kernel/1101.0/01917.html

But Dovecot doesn't pass it recursively. It's only passed once from
pop3-login to pop3 process.
> Is this something that Dovecot should be able to handle, or is it strictly
> Debian/libc/MySillyMistake related?
> 
> #uname -a
> Linux server 3.16.0-4-amd64 #1 SMP Debian 3.16.7-ckt20-1+deb8u3
> (2016-01-17) x86_64 GNU/Linux
I wonder if there's a new kernel change that started detecting the recursion
wrong.

El vie., 11 mar. 2016 a las 2:08, Timo Sirainen (<tss at iki.fi>)
escribi?:
> On 11 Mar 2016, at 03:48, Luis Ugalde <forondarena at gmail.com>
wrote:
> >
> > Hi,
> >
> > I'm starting to see, on a pretty standard Debian Jessie
installation,
> some
> > error messages that are apparently related to the ETOOMANYREFS errno.
> >
> > Firstly, the mail log shows this:
> > dovecot: pop3-login: Error: fd_send(pop3, 18) failed: Too many
> references:
> > cannot splice
>
> Apparently because Linux thinks the same fd has been passed around
> recursively too many times:
> http://lkml.iu.edu/hypermail/linux/kernel/1101.0/01917.html
>
> But Dovecot doesn't pass it recursively. It's only passed once from
> pop3-login to pop3 process.
>
> > Is this something that Dovecot should be able to handle, or is it
> strictly
> > Debian/libc/MySillyMistake related?
> >
> > #uname -a
> > Linux server 3.16.0-4-amd64 #1 SMP Debian 3.16.7-ckt20-1+deb8u3
> > (2016-01-17) x86_64 GNU/Linux
>
> I wonder if there's a new kernel change that started detecting the
> recursion wrong.
>
>
Yes, It's started to happen with the latest kernels from the Stable branch.
This is the latest I have installed:
3.16.0-4-amd64 #1 SMP Debian 3.16.7-ckt20-1+deb8u3 (2016-01-17) x86_64

Older Debian kernels are not showing up anything. This one, for example:
 3.16.0-4-amd64 #1 SMP Debian 3.16.7-ckt11-1+deb8u6 (2015-11-09) x86_64


Regards.