Subject: Re: [bug] __nf_ct_refresh_acct(): WARNING: at lib/list_debug.c:30 __list_add+0x7d/0xad()

From: Ingo Molnar <[email-masked]>
Date: Thu, 18 Jun 2009 07:23:56 +0200

* Ingo Molnar <[email-masked]> wrote:

> > IPS_CONFIRMED_BIT is set under nf_conntrack_lock (in 
> > __nf_conntrack_confirm()), we probably want to add a 
> > synchronisation under ct->lock as well, or 
> > __nf_ct_refresh_acct() could set ct->timeout.expires to 
> > extra_jiffies, while a different cpu could confirm the 
> > conntrack.
> > 
> > Following patch as RFC
> 
> A quick test suggests that it seems to works here - thanks Eric!

a test-box still triggered this crash overnight:

[  252.433471] ------------[ cut here ]------------
[  252.436031] WARNING: at lib/list_debug.c:30 __list_add+0x95/0xa0()
[  252.436031] Hardware name: System Product Name
[  252.436031] list_add corruption. prev->next should be next (ffff88003fa1d460), but was ffffffff82e560a0. (prev=ffff880003b458c0).
[  252.436031] Pid: 7348, comm: ssh Tainted: G        W  2.6.30-tip #54604
[  252.436031] Call Trace:
[  252.436031]  [<ffffffff8149eda5>] ? __list_add+0x95/0xa0
[  252.436031]  [<ffffffff8105c79b>] warn_slowpath_common+0x7b/0xd0
[  252.436031]  [<ffffffff8105c851>] warn_slowpath_fmt+0x41/0x50
[  252.436031]  [<ffffffff8149eda5>] __list_add+0x95/0xa0
[  252.436031]  [<ffffffff8106937e>] internal_add_timer+0x9e/0xf0
[  252.436031]  [<ffffffff8106a5ef>] mod_timer+0x10f/0x160
[  252.436031]  [<ffffffff8106a658>] add_timer+0x18/0x20
[  252.436031]  [<ffffffff81f6e42a>] __nf_conntrack_confirm+0x1da/0x3c0
[  252.436031]  [<ffffffff81fdb8dd>] ipv4_confirm+0xfd/0x160
[  252.436031]  [<ffffffff81f6a130>] nf_iterate+0x70/0xd0
[  252.436031]  [<ffffffff81f99180>] ? ip_finish_output+0x0/0x380
[  252.436031]  [<ffffffff81f6a4c4>] nf_hook_slow+0xe4/0x160
[  252.436031]  [<ffffffff81f99180>] ? ip_finish_output+0x0/0x380
[  252.436031]  [<ffffffff81f995f5>] ip_output+0xf5/0x110
[  252.436031]  [<ffffffff81f96b05>] ip_local_out+0x25/0x40
[  252.436031]  [<ffffffff81f97434>] ip_queue_xmit+0x224/0x420
[  252.436031]  [<ffffffff81111118>] ? __kmalloc_node_track_caller+0xd8/0x1f0
[  252.436031]  [<ffffffff8108df19>] ? trace_hardirqs_on_caller+0x29/0x1f0
[  252.436031]  [<ffffffff81fae0dd>] tcp_transmit_skb+0x50d/0x7e0
[  252.436031]  [<ffffffff81faf547>] tcp_connect+0x3c7/0x500
[  252.436031]  [<ffffffff81fb4693>] tcp_v4_connect+0x433/0x520
[  252.436031]  [<ffffffff81fc446f>] inet_stream_connect+0x22f/0x2d0
[  252.436031]  [<ffffffff81118719>] ? fget_light+0x19/0x110
[  252.436031]  [<ffffffff81f294b8>] sys_connect+0xb8/0xd0
[  252.436031]  [<ffffffff8100ccf9>] ? retint_swapgs+0x13/0x1b
[  252.436031]  [<ffffffff8108df19>] ? trace_hardirqs_on_caller+0x29/0x1f0
[  252.436031]  [<ffffffff8217a49f>] ? trace_hardirqs_on_thunk+0x3a/0x3f
[  252.436031]  [<ffffffff8100c252>] system_call_fastpath+0x16/0x1b
[  252.436031] ---[ end trace a7919e7f17c0a73d ]---

With your patch (repeated below) applied. Is Patrick's alternative 
patch supposed to fix something that yours does not?

	Ingo

------------------>
From 16b663c1ac11c31d05a0768eb9aeba743b4f49ed Mon Sep 17 00:00:00 2001
From: Eric Dumazet <[email-masked]>
Date: Wed, 17 Jun 2009 12:18:27 +0200
Subject: [PATCH] net: Fix: __nf_ct_refresh_acct(): WARNING: at lib/list_debug.c:30 __list_add+0x7d/0xad()
MIME-Version: 1.0
Content-Type: text/plain; charset=utf-8
Content-Transfer-Encoding: 8bit

Ingo Molnar a écrit :
> here's another bug i triggered today - some sort of memory/list
> corruption going on in the timer code. Then i turned on debugobjects
> and got a pretty specific assert in the TCP code:
>
> [   48.320340] ------------[ cut here ]------------
> [   48.324031] WARNING: at lib/list_debug.c:30 __list_add+0x7d/0xad()
> [   48.324031] Hardware name: System Product Name
> [   48.324031] list_add corruption. prev->next should be next (ffffffff81fe2280), but was ffff88003f901440. (prev=ffff880002a9bcf0).
> [   48.324031] Modules linked in:
> [   48.324031] Pid: 0, comm: swapper Tainted: G        W  2.6.30-tip #54394
> [   48.324031] Call Trace:
> [   48.324031]  <IRQ>  [<ffffffff812b3098>] ? __list_add+0x7d/0xad
> [   48.324031]  [<ffffffff810581a2>] warn_slowpath_common+0x8d/0xd0
> [   48.324031]  [<ffffffff81058272>] warn_slowpath_fmt+0x50/0x66
> [   48.324031]  [<ffffffff812b3098>] __list_add+0x7d/0xad
> [   48.324031]  [<ffffffff810650c3>] internal_add_timer+0xd1/0xe7
> [   48.324031]  [<ffffffff81065797>] __mod_timer+0x107/0x139
> [   48.324031]  [<ffffffff810658cb>] mod_timer_pending+0x28/0x3e
> [   48.324031]  [<ffffffff8163d5d3>] __nf_ct_refresh_acct+0x71/0xf9
> [   48.324031]  [<ffffffff81643d92>] tcp_packet+0x60c/0x6a2
> [   48.324031]  [<ffffffff8163da60>] ? nf_conntrack_find_get+0xb7/0xef
> [   48.324031]  [<ffffffff8163d9a9>] ? nf_conntrack_find_get+0x0/0xef
> [   48.324031]  [<ffffffff8163f0fd>] nf_conntrack_in+0x3a3/0x534
> [   48.324031]  [<ffffffff81665a5c>] ? ip_rcv_finish+0x0/0x3bc
> [   48.324031]  [<ffffffff816a48b1>] ipv4_conntrack_in+0x34/0x4a
> [   48.324031]  [<ffffffff8163a79f>] nf_iterate+0x5d/0xb1
> [   48.324031]  [<ffffffff81012cd6>] ? ftrace_call+0x5/0x2b
> [   48.324031]  [<ffffffff81665a5c>] ? ip_rcv_finish+0x0/0x3bc
> [   48.324031]  [<ffffffff8163a897>] nf_hook_slow+0xa4/0x133
> [   48.324031]  [<ffffffff81665a5c>] ? ip_rcv_finish+0x0/0x3bc
> [   48.324031]  [<ffffffff816660c6>] ip_rcv+0x2ae/0x30d
> [   48.324031]  [<ffffffff816139f0>] ? netpoll_rx+0x14/0x9d
> [   48.324031]  [<ffffffff81613e2a>] netif_receive_skb+0x3b1/0x402
> [   48.324031]  [<ffffffff81613bf4>] ? netif_receive_skb+0x17b/0x402
> [   48.324031]  [<ffffffff81607661>] ? skb_pull+0xd/0x59
> [   48.324031]  [<ffffffff8162a0c5>] ? eth_type_trans+0x48/0x104
> [   48.324031]  [<ffffffff814cfc21>] nv_rx_process_optimized+0x15a/0x227
> [   48.324031]  [<ffffffff814d3326>] nv_napi_poll+0x2a9/0x2cd
> [   48.324031]  [<ffffffff81611aeb>] net_rx_action+0xd1/0x249
> [   48.324031]  [<ffffffff81611c02>] ? net_rx_action+0x1e8/0x249
> [   48.324031]  [<ffffffff8105f758>] __do_softirq+0xcb/0x1bb
> [   48.324031]  [<ffffffff8101420c>] call_softirq+0x1c/0x30
> [   48.324031]  [<ffffffff810164cb>] do_softirq+0x5f/0xd7
> [   48.324031]  [<ffffffff8105f0a4>] irq_exit+0x66/0xb9
> [   48.324031]  [<ffffffff817c1fc3>] do_IRQ+0xbb/0xe8
> [   48.324031]  [<ffffffff81def140>] ? early_idt_handler+0x0/0x71
> [   48.324031]  [<ffffffff810139d3>] ret_from_intr+0x0/0x16
> [   48.324031]  <EOI>  [<ffffffff8101c938>] ? default_idle+0x59/0x9d
> [   48.324031]  [<ffffffff81088399>] ? trace_hardirqs_on+0x20/0x36
> [   48.324031]  [<ffffffff810301a9>] ? native_safe_halt+0xb/0xd
> [   48.324031]  [<ffffffff810301a7>] ? native_safe_halt+0x9/0xd
> [   48.324031]  [<ffffffff8101c93d>] ? default_idle+0x5e/0x9d
> [   48.324031]  [<ffffffff810b9cbd>] ? stop_critical_timings+0x3d/0x54
> [   48.324031]  [<ffffffff81011feb>] ? cpu_idle+0xbe/0x107
> [   48.324031]  [<ffffffff81def140>] ? early_idt_handler+0x0/0x71
> [   48.324031]  [<ffffffff8177f135>] ? rest_init+0x79/0x8f
> [   48.324031]  [<ffffffff81def140>] ? early_idt_handler+0x0/0x71
> [   48.324031]  [<ffffffff81deff5d>] ? start_kernel+0x2d8/0x2f3
> [   48.324031]  [<ffffffff81def140>] ? early_idt_handler+0x0/0x71
> [   48.324031]  [<ffffffff81def2a4>] ? x86_64_start_reservations+0x8f/0xaa
> [   48.324031]  [<ffffffff81def000>] ? __init_begin+0x0/0x140
> [   48.324031]  [<ffffffff81def3c3>] ? x86_64_start_kernel+0x104/0x127
> [   48.324031] ---[ end trace 5a5d197966b56a31 ]---
> modprobe: FATAL: Could not load /lib/modules/2.6.30-tip/modules.dep: No such file or directory
>
> this too is a new pattern. Config and full bootlog attached.
>
> Unfortunately it's not clearly reproducible - needs some networking
> load to trigger, and sometimes the symptoms are just a straight hang
> (with no console messages) - so not very bisection friendly.
>
> 	Ingo
>

commit 65cb9fda32be613216f601a330b311c3bd7a8436 seems the origin...
(and/or 440f0d588555892601cfe511728a0fc0c8204063)

commit 65cb9fda32be613216f601a330b311c3bd7a8436
Author: Patrick McHardy <[email-masked]>
Date:   Sat Jun 13 12:21:49 2009 +0200

    netfilter: nf_conntrack: use mod_timer_pending() for conntrack refresh

    Use mod_timer_pending() instead of atomic sequence of del_timer()/
    add_timer(). mod_timer_pending() does not rearm an inactive timer,
    so we don't need the conntrack lock anymore to make sure we don't
    accidentally rearm a timer of a conntrack which is in the process
    of being destroyed.

    With this change, we don't need to take the global lock anymore at all,
    counter updates can be performed under the per-conntrack lock.

    Signed-off-by: Patrick McHardy <[email-masked]>
Cc: David Miller <[email-masked]>
Cc: [email-masked]
Cc: [email-masked]
Cc: Patrick McHardy <[email-masked]>
LKML-Reference: <[email-masked]>
Signed-off-by: Ingo Molnar <[email-masked]>
IPS_CONFIRMED_BIT is set under nf_conntrack_lock (in __nf_conntrack_confirm()),
we probably want to add a synchronisation under ct->lock as well,
or __nf_ct_refresh_acct() could set ct->timeout.expires to extra_jiffies,
while a different cpu could confirm the conntrack.

Following patch as RFC
---
 net/netfilter/nf_conntrack_core.c |    7 +++++--
 1 files changed, 5 insertions(+), 2 deletions(-)

diff --git a/net/netfilter/nf_conntrack_core.c b/net/netfilter/nf_conntrack_core.c
index 5f72b94..24034c4 100644
--- a/net/netfilter/nf_conntrack_core.c
+++ b/net/netfilter/nf_conntrack_core.c
@@ -408,6 +408,7 @@ __nf_conntrack_confirm(struct sk_buff *skb)
 	NF_CT_ASSERT(!nf_ct_is_confirmed(ct));
 	pr_debug("Confirming conntrack %p\n", ct);
 
+	spin_lock_bh(&ct->lock);
 	spin_lock_bh(&nf_conntrack_lock);
 
 	/* See if there's one in the list already, including reverse:
@@ -435,6 +436,7 @@ __nf_conntrack_confirm(struct sk_buff *skb)
 	set_bit(IPS_CONFIRMED_BIT, &ct->status);
 	NF_CT_STAT_INC(net, insert);
 	spin_unlock_bh(&nf_conntrack_lock);
+	spin_unlock_bh(&ct->lock);
 	help = nfct_help(ct);
 	if (help && help->helper)
 		nf_conntrack_event_cache(IPCT_HELPER, ct);
@@ -446,6 +448,7 @@ __nf_conntrack_confirm(struct sk_buff *skb)
 out:
 	NF_CT_STAT_INC(net, insert_failed);
 	spin_unlock_bh(&nf_conntrack_lock);
+	spin_unlock_bh(&ct->lock);
 	return NF_DROP;
 }
 EXPORT_SYMBOL_GPL(__nf_conntrack_confirm);
@@ -848,6 +851,7 @@ void __nf_ct_refresh_acct(struct nf_conn *ct,
 	NF_CT_ASSERT(ct->timeout.data == (unsigned long)ct);
 	NF_CT_ASSERT(skb);
 
+	spin_lock_bh(&ct->lock);
 	/* Only update if this is not a fixed timeout */
 	if (test_bit(IPS_FIXED_TIMEOUT_BIT, &ct->status))
 		goto acct;
@@ -871,13 +875,12 @@ acct:
 
 		acct = nf_conn_acct_find(ct);
 		if (acct) {
-			spin_lock_bh(&ct->lock);
 			acct[CTINFO2DIR(ctinfo)].packets++;
 			acct[CTINFO2DIR(ctinfo)].bytes +=
 				skb->len - skb_network_offset(skb);
-			spin_unlock_bh(&ct->lock);
 		}
 	}
+	spin_unlock_bh(&ct->lock);
 }
 EXPORT_SYMBOL_GPL(__nf_ct_refresh_acct);