netdev - Re: WARNING: at include/net/sock.h:417 udp_lib

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Date:	Tue, 07 Jul 2009 09:21:47 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Emil S Tantilov <emils.tantilov@...il.com>
CC:	"Tantilov, Emil S" <emil.s.tantilov@...el.com>,
	NetDev <netdev@...r.kernel.org>,
	"Brandeburg, Jesse" <jesse.brandeburg@...el.com>,
	"Kirsher, Jeffrey T" <jeffrey.t.kirsher@...el.com>,
	Jiri Olsa <jolsa@...hat.com>,
	"David S. Miller" <davem@...emloft.net>
Subject: Re: WARNING: at include/net/sock.h:417 udp_lib_unhash

Emil S Tantilov a écrit :
> On Wed, Jul 1, 2009 at 11:10 PM, Eric Dumazet<eric.dumazet@...il.com> wrote:
>> Tantilov, Emil S a écrit :
>>> I see the following trace during netperf stress mixed UDP/TCP IPv4/6 traffic. This is on recent pulls from net-2.6 and net-next.
>>>
>>> [45197.989163] ------------[ cut here ]------------
>>> [45197.994309] WARNING: at include/net/sock.h:417 udp_lib_unhash+0x81/0xab()
>>> [45197.994311] Hardware name: X7DA8
>>> [45197.994314] Modules linked in: e1000 [last unloaded: e1000]
>>> [45197.994326] Pid: 7110, comm: netserver Tainted: G        W  2.6.31-rc1-net-next-e1000-06250902 #8
>>> [45197.994331] Call Trace:
>>> [45197.994336]  [<ffffffff8135e0dc>] ? udp_lib_unhash+0x81/0xab
>>> [45197.994344]  [<ffffffff8103cac9>] warn_slowpath_common+0x77/0x8f
>>> [45197.994349]  [<ffffffff8103caf0>] warn_slowpath_null+0xf/0x11
>>> [45197.994352]  [<ffffffff8135e0dc>] udp_lib_unhash+0x81/0xab
>>> [45197.994357]  [<ffffffff81301acb>] sk_common_release+0x2f/0xb4
>>> [45197.994364]  [<ffffffff813a0256>] udp_lib_close+0x9/0xb
>>> [45197.994369]  [<ffffffff81364259>] inet_release+0x58/0x5f
>>> [45197.994374]  [<ffffffff8138c8bd>] inet6_release+0x30/0x35
>>> [45197.994383]  [<ffffffff812ff273>] sock_release+0x1a/0x6c
>>> [45197.994386]  [<ffffffff812ff763>] sock_close+0x22/0x26
>>> [45197.994392]  [<ffffffff810c69a0>] __fput+0xf0/0x18c
>>> [45197.994395]  [<ffffffff810c6d00>] fput+0x15/0x19
>>> [45197.994399]  [<ffffffff810c3c3e>] filp_close+0x5c/0x67
>>> [45197.994404]  [<ffffffff810c3cc4>] sys_close+0x7b/0xb6
>>> [45197.994412]  [<ffffffff8100baeb>] system_call_fastpath+0x16/0x1b
>>> [45197.994418] ---[ end trace 5acab6fc0afdaaa3 ]---
>>>
>>> Emil--
>> Thanks for this report Emil.
>>
>> I could not find a recent change in this area in last kernels.
>> If struct sk is hashed (sk_hashed() true), then sk_refcnt was incremented
>> in sk_nulls_add_node_rcu(), thus its value should be >= 2.
>>
>> Maybe we have a missing memory barrier somewhere or a list corruption.
>>
>> 1) Could you try CONFIG_DEBUG_LIST=y ?
> I am running a test with this option now. Sorry for the delayed
> response, I was out last week.
> 
>> 2) Could you give model of cpu, since it reminds me the ongoing discussion raised by Jiri Olsa.
> 
> processor	: 0
> vendor_id	: GenuineIntel
> cpu family	: 6
> model		: 23
> model name	: Intel(R) Xeon(R) CPU           E5450  @ 3.00GHz
> stepping	: 6
> cpu MHz		: 2999.790
> cache size	: 6144 KB
> physical id	: 0
> siblings	: 4
> core id		: 0
> cpu cores	: 4
> apicid		: 0
> initial apicid	: 0
> fpu		: yes
> fpu_exception	: yes
> cpuid level	: 10
> wp		: yes
> flags		: fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov
> pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe syscall nx
> lm constant_tsc arch_perfmon pebs bts rep_good pni dtes64 monitor
> ds_cpl vmx est tm2 ssse3 cx16 xtpr pdcm dca sse4_1 lahf_lm tpr_shadow
> vnmi flexpriority
> bogomips	: 5999.58
> clflush size	: 64
> 
> 2 quad core Xeons, I only included the output from the first to reduce clutter.
> 
>> CPU1 does an atomic_inc(&sk->sk_refcnt)  : refcnt changes from 1 to 2
>> then CPU2 does an atomic_read(&sk->sk_refcnt) and reads 1 instead of 2
>>
>> David, maybe this test is not safe and if we really want to do a check
>> we need to use a stronger atomic function.
>>
>> If you can reproduce this problem easily could you try following patch ?
> 
> It varies from few minutes to hours, but it does reproduce
> consistently in my tests so far. I will try your patch once I manage
> to get a trace with CONFIG_DEBUG_LIST
> 


Eventually, could you also use following debug/quick&dirty patch ?


diff --git a/include/net/sock.h b/include/net/sock.h
index 352f06b..548f822 100644
--- a/include/net/sock.h
+++ b/include/net/sock.h
@@ -376,6 +376,7 @@ static __inline__ int __sk_del_node_init(struct sock *sk)
 
 static inline void sock_hold(struct sock *sk)
 {
+	WARN_ON(atomic_read(&sk->sk_refcnt) == 0);
 	atomic_inc(&sk->sk_refcnt);
 }
 
@@ -385,6 +386,7 @@ static inline void sock_hold(struct sock *sk)
 static inline void __sock_put(struct sock *sk)
 {
 	atomic_dec(&sk->sk_refcnt);
+	WARN_ON(atomic_read(&sk->sk_refcnt) == 0);
 }
 
 static __inline__ int sk_del_node_init(struct sock *sk)

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