file descripter leak in current with Qmail?

[Arjan van Leeuwen]

Hi,

On Monday 07 June 2004 19:06, Robert Watson wrote:
> On Mon, 7 Jun 2004, David A. Benfell wrote:
(...)
>
> However, I think the more serious element here is the reason why you reach
> the limit: this happens "naturally" under some workloads simply because of
> large numbers of open files and network connections.  However, in some
> workloads, it's a symptom of a system or application bug, such as a
> resource leak.
>
> Because the resources were returned when qmail was killed, that largely
> eliminates the possibility of a kernel resource leak (not entirely, but
> largely), as most kernel resource leaks involving file descriptors have
> the symptom that even after the process exits, the resources aren't
> release (i.e., a reference counting bug or race).  This suggests a user
> space issue -- that doesn't eliminate a system bug, as it could be a bug
> in a library that manages descriptors, but it also suggests the
> possibility of an application bug, or at least, a poor application
> interaction with a system bug.  Occasionally, we've seen bugs in the
> threading libraries that result in leaked descriptors, but my recollection
> is that qmail doesn't use threads.  So that suggests either a support
> library (perhaps crypto or the like), or qmail itself.  Or that you just
> hit an extremely high load. :-)
>
> In terms of debugging it: your first task it to identify if there's one
> process that's holding all the fd's, or if it is distributed over many
> proceses.  After that, you want to track down what kind of fd is being
> left open, which may help you track down why it's left open...

Just as I'm reading this, I'm seeing the same thing on my -CURRENT server, 
which has a _very_ low load (atm, it's only routing the internet traffic for 
3 users and serving SMTP for 2 of them). I'm also running qmail. The kernel 
is from June 6. How do I go about investigating this further?

Best regards,

Arjan van Leeuwen
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