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

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 [off-list ref]
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 [off-list ref]



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

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);