Re: ip_conntrack related slab error (Re: Fw: Re: 2.6.16-rc1-mm3)

From: Reuben Farrelly
Date: Tue Jan 31 2006 - 05:04:44 EST


On 31/01/2006 10:24 p.m., Harald Welte wrote:
Begin forwarded message:

Date: Sat, 28 Jan 2006 00:47:06 +1300
From: Reuben Farrelly <reuben-lkml@xxxxxxxx>
To: Andrew Morton <akpm@xxxxxxxx>
Cc: linux-kernel@xxxxxxxxxxxxxxx, netdev@xxxxxxxxxxxxxxx
Subject: Re: 2.6.16-rc1-mm3

Just triggered this one, which had a fairly bad effect on connectivity to the box:

i2c /dev entries driver
slab error in kmem_cache_destroy(): cache `ip_conntrack': Can't free all objects
[<b010412b>] show_trace+0xd/0xf
[<b01041cc>] dump_stack+0x17/0x19
[<b0155d04>] kmem_cache_destroy+0x9b/0x1a9
[<f0ebf701>] ip_conntrack_cleanup+0x5d/0x10e [ip_conntrack]
[<f0ebe31e>] init_or_cleanup+0x1f8/0x283 [ip_conntrack]
[<f0ec2c4e>] fini+0xa/0x66 [ip_conntrack]
[<b0136d06>] sys_delete_module+0x161/0x1fb
[<b0102b3f>] sysenter_past_esp+0x54/0x75
Removing netfilter NETLINK layer.
[root@tornado log]#

I was just reading IMAP mail at the time, ie same as I'd been doing for an hour or two beforehand and not altering config of the box in any way. I was able to log on via console but lost all network connectivity and had to reboot :(

The codepath you see in that backtrace is only hit during load or
removal of the 'ip_conntrack' module. While this certainly still should
not oops, your description of 'not doing anything but IMAP reading' is
certainly not true.

With the greatest of respect (which I do have for you Harald), I don't think being essentially called a liar is very fair.

I've no reason to not report exactly what I observed and noted and what I did or didn't do before noting it, and while you may argue that it doesn't match with what you expect, that doesn't mean that I'm making stuff up. More likely it means that neither you or I understand quite what was happening at the time.

Could you please describe what actually happened when that bug happened?
It looks to me that you were unloading ip_conntrack_netlink.ko followed
by ip_conntrack.ko.

It's now four days later. I wrote the email a few minutes after noting the oops, so if I was fiddling with iptables at the time I'm sure I would have said so. I mean, why wouldn't I?

I'll try to reproduce it, but as I've no idea what triggered it in the first place it may be a bit tricky.

Noting that a reboot of the box does not even load the ip_conntrack_netlink module, which if I was indeed messing with it, I would have probably had to force the module to load. I think I'd know if I was doing that.........

Generic details such as .config is at http://www.reub.net/files/kernel/

You don't have permission to access /files/kernel/ on this server.

Apologies. My bad, it's fixed now.

Anyway, let's get to the bottom of the problem rather than get personal about what actually happened.

Reuben

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