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SubjectRe: kernel panic: bug in sch_sfq.c
Hi devik!

In this case, I added the rules the morning, but there was no traffic
flowing through the machine. That evening we redirected traffic through the
box (so HTB obviously kicked in). About 10 minutes later it crashed.

I think the only common thing I've seen so far is that it crashes when htb
is actually doing a lot of shaping/prioritizing - that doesn't help much.

Also, if I compile the kernel with all debugging enabled (CONFIG_DEBUG_SLAB,
etc) I can reliably trigger the BUG() on line 1263 in mm/slab.c - don't know
if this is related to the HTB problem - I've tested this on many different
machines with many different kernels. If I disable CONFIG_DEBUG_SLAB, I
don't get that (obviously). The first crash since I've started disabling
CONFIG_DEBUG_SLAB on our Linux QoS boxes have been this one.

> Hmm,
> I looked at it. It seems that skb linked list was corrupted
> (containing NULL pointer). It could be because of two problems,
> either someone (maybe htb too)'ve overwritten memory or HTB
> called dequeue with wrong argument.
> Latter is unlikely because I call q->dequeue and sfq's
> dequeue was really called. Thus pointer is ok.
> Let's examine how could HTB mungle with qdisc internals. If
> htb would think that leaf is inner node, inner.feed[0] is
> pointer equal to leaf.q. I examined code but there is no
> way to make this mistake.
>
> Last 3 days I got 3 bugreports. Each crashes in different
> place and all seem unrelated. Each is NULL pointer dereference
> though.
> I think there is some place in some code which writes in
> bad random places in memory :-\
>
> To ask all people whose have seen such Oops, have you used
> dynamic tc classes changes ? Like creating/deleting/changing/viewving
> classes offten at runtime ? (I'm trying to find common trigger).
>
> thanks, devik
> HTB maintainer
>
> On Tue, 11 Mar 2003, bert hubert wrote:
>
> > On Tue, Mar 11, 2003 at 11:14:09AM +0200, Abraham van der Merwe wrote:
> > > Hi!
> > >
> > > I have a box that crashed today. Below is the decoded kernel panic. If you
> > > track down the bug PLEASE send me a patch.
> >
> > Weird, Alexeys code is normally very very solid. Perhaps HTB is also
> > involved. Devik?
> >
> > >
> > > ------------< snip <------< snip <------< snip <------------
> > > ksymoops 2.4.8 on i686 2.4.20-rc1. Options used
> > > -v vmlinux-2.4.21-pre5 (specified)
> > > -K (specified)
> > > -L (specified)
> > > -O (specified)
> > > -m System.map-2.4.21-pre5 (specified)
> > >
> > > Unable to handle kernel NULL pointer dereference at virtual address 00000004
> > > *pde = 00000000
> > > Oops: 0002
> > > CPU: 0
> > > EIP: 0010:[<c01a5399>] Not tainted
> > > Using defaults from ksymoops -t elf32-i386 -a i386
> > > EFLAGS: 00010202
> > > eax: 00000000 ebx: c7b9a9e8 ecx: 0000007f edx: c7a8eef8
> > > esi: c7b9ab08 edi: 000007f0 ebp: c7a8e060 esp: c021deb8
> > > ds: 0018 es: 0018 ss: 0018
> > > Process swapper (pid: 0, stackpage=c021d000)
> > > Stack: c7b9a9e8 c7b9ab08 c7f7ee00 c7b9a860 c7b893c0 c7f7ee00 c7b9a860 00000000
> > > c01a3507 c7b5c680 7fb9a9f0 c01a339e c7a8e000 ffffffff 00000018 00000006
> > > c7b9a800 00000018 00000006 c7b9a800 c7b9a9e8 c7b9ab08 c7f7ee00 c01a371c
> > > Call Trace: [<c01a3507>] [<c01a339e>] [<c01a371c>] [<c019f7a3>] [>c019949d>]
> > > [<c0115a6a>] [<c01082bd>] [<c0105240>] [<c0105240>] [<c010a528>] [<c0105240>]
> > > [<c0105240>] [<c0105263>] [<c01052d2>] [<c0105000>] [<c0105027>]
> > > Code: 89 50 04 89 02 8b 5c 24 24 c7 03 00 00 00 00 c7 43 04 00 00
> > >
> > >
> > > >>EIP; c01a5399 <sfq_dequeue+59/1b0> <=====
> > >
> > > >>esp; c021deb8 <init_task_union+1eb8/2000>
> > >
> > > Trace; c01a3507 <htb_dequeue_tree+217/230>
> > > Trace; c01a339e <htb_dequeue_tree+ae/230>
> > > Trace; c01a371c <htb_dequeue+16c/250>
> > > Trace; c019f7a3 <qdisc_restart+13/d0>
> > > Trace; c0115a6a <do_softirq+5a/b0>
> > > Trace; c01082bd <do_IRQ+9d/b0>
> > > Trace; c0105240 <default_idle+0/30>
> > > Trace; c0105240 <default_idle+0/30>
> > > Trace; c010a528 <call_do_IRQ+5/d>
> > > Trace; c0105240 <default_idle+0/30>
> > > Trace; c0105240 <default_idle+0/30>
> > > Trace; c0105263 <default_idle+23/30>
> > > Trace; c01052d2 <cpu_idle+42/60>
> > > Trace; c0105000 <_stext+0/0>
> > > Trace; c0105027 <rest_init+27/30>
> > >
> > > Code; c01a5399 <sfq_dequeue+59/1b0>
> > > 00000000 <_EIP>:
> > > Code; c01a5399 <sfq_dequeue+59/1b0> <=====
> > > 0: 89 50 04 mov %edx,0x4(%eax) <=====
> > > Code; c01a539c <sfq_dequeue+5c/1b0>
> > > 3: 89 02 mov %eax,(%edx)
> > > Code; c01a539e <sfq_dequeue+5e/1b0>
> > > 5: 8b 5c 24 24 mov 0x24(%esp,1),%ebx
> > > Code; c01a53a2 <sfq_dequeue+62/1b0>
> > > 9: c7 03 00 00 00 00 movl $0x0,(%ebx)
> > > Code; c01a53a8 <sfq_dequeue+68/1b0>
> > > f: c7 43 04 00 00 00 00 movl $0x0,0x4(%ebx)
> > >
> > > <0>Kernel panic: Aiee, killing interrupt handler!
> > > ------------< snip <------< snip <------< snip <------------
> > >
> > > Below are the rules that were installed on the system:
> > >
> > > ------------< snip <------< snip <------< snip <------------
> > > /sbin/tc qdisc del dev eth0 root
> > > /sbin/tc qdisc del dev eth1 root
> > > /sbin/iptables -t mangle -F qos
> > > /sbin/iptables -t mangle -Z qos
> > > /sbin/tc qdisc add dev eth0 root handle 1: htb default 5 r2q 1
> > > /sbin/tc class add dev eth0 parent 1: classid 1:1 htb rate 96kbit
> > > /sbin/tc class add dev eth0 parent 1:1 classid 1:2 htb rate 96kbit ceil 96kbit
> > > /sbin/tc class add dev eth0 parent 1:2 classid 1:3 htb rate 48kbit ceil 96kbit prio 1
> > > /sbin/tc qdisc add dev eth0 handle 3: parent 1:3 sfq perturb 10 limit 31
> > > /sbin/tc class add dev eth0 parent 1:2 classid 1:4 htb rate 24kbit ceil 96kbit prio 1
> > > /sbin/tc qdisc add dev eth0 handle 4: parent 1:4 sfq perturb 10 limit 31
> > > /sbin/tc class add dev eth0 parent 1:2 classid 1:5 htb rate 16kbit ceil 96kbit prio 2
> > > /sbin/tc qdisc add dev eth0 handle 5: parent 1:5 sfq perturb 10 limit 31
> > > /sbin/iptables -t mangle -A qos -o eth0 -s 66.8.85.0/28 -j CLASSIFY --set-class 1:3
> > > /sbin/iptables -t mangle -A qos -o eth0 -s 66.8.85.80/28 -j CLASSIFY --set-class 1:4
> > > /sbin/iptables -t mangle -A qos -o eth0 -s 192.116.106.192/29 -j CLASSIFY --set-class 1:0
> > > /sbin/iptables -t mangle -A qos -o eth0 -s 66.8.28.48/29 -j CLASSIFY --set-class 1:0
> > > /sbin/tc qdisc add dev eth1 root handle 1: htb default 5 r2q 2
> > > /sbin/tc class add dev eth1 parent 1: classid 1:1 htb rate 512kbit
> > > /sbin/tc class add dev eth1 parent 1:1 classid 1:2 htb rate 256kbit ceil 512kbit
> > > /sbin/tc class add dev eth1 parent 1:2 classid 1:3 htb rate 128kbit ceil 512kbit prio 1
> > > /sbin/tc qdisc add dev eth1 handle 3: parent 1:3 sfq perturb 10 limit 169
> > > /sbin/tc class add dev eth1 parent 1:2 classid 1:4 htb rate 64kbit ceil 512kbit prio 1
> > > /sbin/tc qdisc add dev eth1 handle 4: parent 1:4 sfq perturb 10 limit 169
> > > /sbin/tc class add dev eth1 parent 1:2 classid 1:5 htb rate 32kbit ceil 512kbit prio 2
> > > /sbin/tc qdisc add dev eth1 handle 5: parent 1:5 sfq perturb 10 limit 169
> > > /sbin/iptables -t mangle -A qos -o eth1 -d 66.8.85.0/28 -j CLASSIFY --set-class 1:3
> > > /sbin/iptables -t mangle -A qos -o eth1 -d 66.8.85.80/28 -j CLASSIFY --set-class 1:4
> > > /sbin/iptables -t mangle -A qos -o eth1 -d 192.116.106.192/29 -j CLASSIFY --set-class 1:0
> > > /sbin/iptables -t mangle -A qos -o eth1 -d 66.8.28.48/29 -j CLASSIFY --set-class 1:0
> > > ------------< snip <------< snip <------< snip <------------
> > >
> > > I've made tons of info available on my home page for you to look at (proc
> > > files, vmlinux, System.map, original panic message, etc.
> > >
> > > http://oasis.frogfoot.net/sfq/

> >
> > --
> > http://www.PowerDNS.com Open source, database driven DNS Software
> > http://lartc.org Linux Advanced Routing & Traffic Control HOWTO
> > http://netherlabs.nl Consulting
> >
>
> -
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--

Regards
Abraham

Reporter (to Mahatma Gandhi): Mr Gandhi, what do you think of Western
Civilization?
Gandhi: I think it would be a good idea.

___________________________________________________
Abraham vd Merwe - Frogfoot Networks CC
9 Kinnaird Court, 33 Main Street, Newlands, 7700
Phone: +27 21 686 1674 Cell: +27 82 565 4451
Http: http://www.frogfoot.net/ Email: abz@frogfoot.net

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