Date:	Tue, 2 Jan 2007 08:39:09 +0100
From:	Jarek Poplawski <jarkao2@...pl>
To:	Ben Greear <greearb@...delatech.com>
Cc:	NetDev <netdev@...r.kernel.org>
Subject: Re: BUG: soft lockup detected on CPU#0!  (2.6.18.2 plus hacks)

On Mon, Jan 01, 2007 at 09:00:05PM -0800, Ben Greear wrote:
> I finally had time to look through the code in this backtrace in 
> detail.  I think it *could*
> be a race between ip_rcv and inetdev_init, but I am not certain.  Other 
> than that, I'm real
> low on ideas.  I found a few more stack trace debugging options to 
> enable..perhaps that
> will give a better backtrace if we can reproduce it again.
> 
> I do have lock-debugging enabled, so it should have caught this if was 
> an un-initialized access
> problem, however.
> 
> More details below inline.
> 
> Ben Greear wrote:
> >This is from 2.6.18.2 kernel with my patch set.  The MAC-VLANs are in 
> >active use.
> >From the backtrace, I am thinking this might be a generic problem, 
> >however.
> >
> >Any ideas about what this could be?  It seems to be reproducible every 
> >day or
> >two, but no known way to make it happen quickly...
> >
> >Kernel is SMP, PREEMPT.
> >
> >
> >Dec 19 04:49:33 localhost kernel: BUG: soft lockup detected on CPU#0!
> >Dec 19 04:49:33 localhost kernel:  [<78104252>] show_trace+0x12/0x20
> >Dec 19 04:49:33 localhost kernel:  [<78104929>] dump_stack+0x19/0x20
> >Dec 19 04:49:33 localhost kernel:  [<7814c88b>] softlockup_tick+0x9b/0xd0
> >Dec 19 04:49:33 localhost kernel:  [<7812a992>] 
> >run_local_timers+0x12/0x20
> >Dec 19 04:49:33 localhost kernel:  [<7812ac08>] 
> >update_process_times+0x38/0x80
> >Dec 19 04:49:33 localhost kernel:  [<78112796>] 
> >smp_apic_timer_interrupt+0x66/0x70
> >Dec 19 04:49:33 localhost kernel:  [<78103baa>] 
> >apic_timer_interrupt+0x2a/0x30
> >Dec 19 04:49:33 localhost kernel:  [<78354e8c>] _read_lock+0x3c/0x50
> > Dec 19 04:49:33 localhost kernel:  [<78331f42>] ip_check_mc+0x22/0xb0
> This is blocked on:
> igmp.c:    read_lock(&in_dev->mc_list_lock);
> 
> >Dec 19 04:49:33 localhost kernel:  [<783068bf>] 
> >ip_route_input+0x17f/0xef0
> route.c:            int our = ip_check_mc(in_dev, daddr, saddr, 
> skb->nh.iph->protocol);
> >Dec 19 04:49:33 localhost kernel:  [<78309c59>] ip_rcv+0x349/0x580
> ?? Called by a macro maybe?  Can't find an obvious call to the 

Probably deliver_skb.

> ip_route_input.
> >Dec 19 04:49:33 localhost kernel:  [<782ec98d>] 
> >netif_receive_skb+0x36d/0x3b0
> >Dec 19 04:49:33 localhost kernel:  [<782ee50c>] 
> >process_backlog+0x9c/0x130
> >Dec 19 04:49:33 localhost kernel:  [<782ee795>] net_rx_action+0xc5/0x1f0
> >Dec 19 04:49:33 localhost kernel:  [<78125e58>] __do_softirq+0x88/0x110
> >Dec 19 04:49:33 localhost kernel:  [<78125f59>] do_softirq+0x79/0x80
> >Dec 19 04:49:33 localhost kernel:  [<781260ed>] irq_exit+0x5d/0x60
> >Dec 19 04:49:33 localhost kernel:  [<78105a6d>] do_IRQ+0x4d/0xa0
> >Dec 19 04:49:33 localhost kernel:  [<78103ae9>] 
> >common_interrupt+0x25/0x2c
> >Dec 19 04:49:33 localhost kernel:  [<78354c45>] _spin_lock+0x35/0x50
> >Dec 19 04:49:33 localhost kernel:  [<781aab1d>] proc_register+0x2d/0x110
> >Dec 19 04:49:33 localhost kernel:  [<781ab23d>] 
> >create_proc_entry+0x5d/0xd0
> >Dec 19 04:49:33 localhost kernel:  [<7812873b>] 
> >register_proc_table+0x6b/0x110
> >Dec 19 04:49:33 localhost kernel:  [<78128771>] 
> >register_proc_table+0xa1/0x110
> >Dec 19 04:49:33 localhost last message repeated 3 times
> >Dec 19 04:49:33 localhost kernel:  [<7812886d>] 
> >register_sysctl_table+0x8d/0xc0
> >Dec 19 04:49:33 localhost kernel:  [<7832f0c9>] 
> >devinet_sysctl_register+0x109/0x150
> 
> This devinet_sysctl_register is called right before the ip_mc_init_dev 
> call is made, and
> that call is used to initialize the multicast lock that is blocked on at 
> the top of this backtrace.
> This *could* be the race, but only if the entities in question are the 
> same thing.  I don't see
> any way to determine whether they are or not based on the backtrace.
> 
> I looked through all of the uses of the mc_list_lock, and the places 
> where it does a write_lock
> are few and appear to be correct with no possibility of deadlocking.  If 
> a lock was un-initialized, then
> that could perhaps explain why it is able to deadlock (though, that 
> should have triggered a different
> bug report since I have spin/rw-lock debugging enabled.)
> 

It is hard to say what kind of bug to expect
because at the same time other net_rx_action
with the same vlan dev could take place on
other processor and this inetdev_init could
do more.

The main thing is the possibility of processing
skb with not entirely open source dev which isn't
expected (and checked) by receive functions.
I think the easiest way to convince yourself is
to add temporarily IFF_UP flag checking with
dropping at the beginning of netif_receive_skb and
__vlan_hwaccel_rx.

Jarek P.

> >Dec 19 04:49:33 localhost kernel:  [<7832f2ea>] inetdev_init+0xea/0x160
> >Dec 19 04:49:33 localhost kernel:  [<7832fa2e>] 
> >inet_rtm_newaddr+0x16e/0x190
> >Dec 19 04:49:33 localhost kernel:  [<782f58a9>] 
> >rtnetlink_rcv_msg+0x169/0x230
> >Dec 19 04:49:33 localhost kernel:  [<78300ed0>] 
> >netlink_run_queue+0x90/0x140
> >Dec 19 04:49:33 localhost kernel:  [<782f56dc>] rtnetlink_rcv+0x2c/0x50
> >Dec 19 04:49:33 localhost kernel:  [<783014a5>] 
> >netlink_data_ready+0x15/0x60
> >Dec 19 04:49:33 localhost kernel:  [<78300167>] netlink_sendskb+0x27/0x50
> >Dec 19 04:49:33 localhost kernel:  [<78300bab>] 
> >netlink_unicast+0x15b/0x1f0
> >Dec 19 04:49:33 localhost kernel:  [<783013ab>] 
> >netlink_sendmsg+0x20b/0x2f0
> >Dec 19 04:49:33 localhost kernel:  [<782e12bc>] sock_sendmsg+0xfc/0x120
> >Dec 19 04:49:33 localhost kernel:  [<782e1a5a>] sys_sendmsg+0x10a/0x220
> >Dec 19 04:49:33 localhost kernel:  [<782e3311>] 
> >sys_socketcall+0x261/0x290
> >Dec 19 04:49:33 localhost kernel:  [<7810307d>] 
> >sysenter_past_esp+0x56/0x8d
> >Dec 19 04:52:17 localhost sshd[32311]: gethostby*.getanswer: asked for 
> >"203.60.60.10.in-addr.arpa IN PTR", got type "A"
> >
> 
> 
> -- 
> Ben Greear <greearb@...delatech.com> 
> Candela Technologies Inc  http://www.candelatech.com
> 
> 
> 
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