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Leaking skbuff_heads in 2.2.19 due to pumpd?

To: netdev@xxxxxxxxxxx
Subject: Leaking skbuff_heads in 2.2.19 due to pumpd?
From: Joseph Zbiciak <im14u2c@xxxxxxxxxxxx>
Date: Mon, 1 Oct 2001 10:13:01 -0500
Sender: owner-netdev@xxxxxxxxxxx
User-agent: Mutt/1.2.5i
Hello,

Alan Cox gave me this address to report a problem I'm seeing in
Linux 2.2.19.  I have an old 486 box configured as a masquerading
firewall/web server/squid cache.  It sits on a cablemodem and runs
pumpd to acquire a DHCP lease for our IP address.

It appears that every time pumpd renews our lease, the kernel leaks
about 200 skbuffs.  I noticed this because the number of active
skbuff_heads shown in /proc/slabinfo seemed unusually large prior
to my last reboot (approx 180000).

I rebooted, and then set up a cron job to monitor the "skbuff_head_cache"
line in /proc/slabinfo every 5 minutes, so I could correlate the
increases back to a specific event.  (Prior to that, I had tried
to trigger a leak by exercising the various services on the box,
such as the squid cache, etc. with no success.)  I discovered that
the number of active skbuff_head's would increase by 200 or so
around the same time as pumpd would renew my lease:

/var/log/messages:
Sep 30 23:32:33 asylum pumpd[215]: renewed lease for interface eth0
Oct  1 04:47:37 asylum pumpd[215]: renewed lease for interface eth0

/var/log/skbuff_head.log:  (my adhoc "grep skbuff_head >> log" script)
Sun Sep 30 23:30:00 CDT 2001 skbuff_head_cache   1010   1058
Sun Sep 30 23:35:00 CDT 2001 skbuff_head_cache   1066   1081
Sun Sep 30 23:40:00 CDT 2001 skbuff_head_cache   1211   1219
Sun Sep 30 23:45:00 CDT 2001 skbuff_head_cache   1288   1311
...
Mon Oct  1 04:45:00 CDT 2001 skbuff_head_cache   1290   1311
Mon Oct  1 04:50:00 CDT 2001 skbuff_head_cache   1299   1311
Mon Oct  1 04:55:00 CDT 2001 skbuff_head_cache   1355   1357
Mon Oct  1 05:00:00 CDT 2001 skbuff_head_cache   1447   1449
Mon Oct  1 05:05:00 CDT 2001 skbuff_head_cache   1475   1495


It appears that right after the lease is renewed, other traffic seems
to leak skbuffs.

It's probably worth describing what other sorts of connections are 
open on the box most of the time (and most importantly, are live
across a DCHP lease renewal, which might be why I leak skbuffs after
a renewal):

 -- I typically have one or two rsh connections open to the box
    from another box on the local LAN. 

 -- I have a Jabber client (Gabber) running through a "redir"
    session on the 486.  Redir is a simple proxy program that
    accepts a connection on the "listening" side, and opens a
    connection on my behalf from the firewall box.  (I do this so
    that Gabber doesn't choke when I fire up the VPN software on
    my other box.  I don't run VPN on the 486 in question.)

 -- I often have a remote telnet session into the box open from 
    work.  (Our firewall has a telnet proxy, but not an SSH proxy. 
    *sigh*)

 -- There are a bunch of connections over the loopback interface
    that come from Apache.  I imagine these are for managing the
    child threads:

    tcp   0 0 127.0.0.1:1032 127.0.0.1:1033 ESTABLISHED 
    tcp   0 0 127.0.0.1:1033 127.0.0.1:1032 ESTABLISHED 
    tcp   0 0 127.0.0.1:1030 127.0.0.1:1031 ESTABLISHED 
    tcp   0 0 127.0.0.1:1031 127.0.0.1:1030 ESTABLISHED 
    tcp   0 0 127.0.0.1:1028 127.0.0.1:1029 ESTABLISHED 
    tcp   0 0 127.0.0.1:1029 127.0.0.1:1028 ESTABLISHED 
    tcp   0 0 127.0.0.1:1026 127.0.0.1:1027 ESTABLISHED 
    tcp   0 0 127.0.0.1:1027 127.0.0.1:1026 ESTABLISHED 
    tcp   0 0 127.0.0.1:1024 127.0.0.1:1025 ESTABLISHED 
    tcp   0 0 127.0.0.1:1025 127.0.0.1:1024 ESTABLISHED

So the question is, what might be causing the leak?  Where should I
look?  What information (aside from the above) might be relevant?

I presume this email address goes to a mailing list.  Please copy
me directly on any replies, since I don't presently subscribe to any
of the lists.

Thanks in advance for any insight.  I'd love to help stomp this bug.
It doesn't affect me horribly (that is, I could live with it easily),
but I'd rather not have to reboot once a month when I could instead
help make Linux perfect.  :-)

Regards,

--Joe

--
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