Subject: Re: suspicious RCU usage in xfrm_net_init()

From: Fan Du <[email-masked]>
Date: Thu, 16 Aug 2012 17:36:35 +0800

Hi, Fengguang

Could you please try the below patch, see if spewing still there?
thanks

 From a3f86ecc3ee16ff81d49416bbf791780422988b3 Mon Sep 17 00:00:00 2001
From: Fan Du <[email-masked]>
Date: Thu, 16 Aug 2012 17:31:25 +0800
Subject: [PATCH] Use rcu_dereference_bh to deference pointer protected 
by rcu_read_lock_bh

Signed-off-by: Fan Du <[email-masked]>
---
  net/xfrm/xfrm_policy.c |    2 +-
  1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/net/xfrm/xfrm_policy.c b/net/xfrm/xfrm_policy.c
index 5ad4d2c..75a9d6a 100644
--- a/net/xfrm/xfrm_policy.c
+++ b/net/xfrm/xfrm_policy.c
@@ -2501,7 +2501,7 @@ static void __net_init xfrm_dst_ops_init(struct 
net *net)
  	struct xfrm_policy_afinfo *afinfo;

  	rcu_read_lock_bh();
-	afinfo = rcu_dereference(xfrm_policy_afinfo[AF_INET]);
+	afinfo = rcu_dereference_bh(xfrm_policy_afinfo[AF_INET]);
  	if (afinfo)
  		net->xfrm.xfrm4_dst_ops = *afinfo->dst_ops;
  #if IS_ENABLED(CONFIG_IPV6)
-- 
1.7.1

On 2012年08月16日 15:37, Fengguang Wu wrote:
> Hi Priyanka,
>
> The below warning shows up, probably related to this commit:
>
> 418a99ac6ad487dc9c42e6b0e85f941af56330f2 Replace rwlock on xfrm_policy_afinfo with rcu
>
> [    0.921216]
> [    0.921645] ===============================
> [    0.922766] [ INFO: suspicious RCU usage. ]
> [    0.923887] 3.5.0-01540-g1669891 #64 Not tainted
> [    0.925123] -------------------------------
> [    0.932860] /c/kernel-tests/src/tip/net/xfrm/xfrm_policy.c:2504 suspicious rcu_dereference_check() usage!
> [    0.935361]
> [    0.935361] other info that might help us debug this:
> [    0.935361]
> [    0.937472]
> [    0.937472] rcu_scheduler_active = 1, debug_locks = 0
> [    0.939182] 2 locks held by swapper/1:
> [    0.940171]  #0:  (net_mutex){+.+.+.}, at: [<ffffffff814e1ad0>] register_pernet_subsys+0x21/0x57
> [    0.942705]  #1:  (rcu_read_lock_bh){......}, at: [<ffffffff822c7329>] xfrm_net_init+0x1e4/0x437
> [    0.951507]
> [    0.951507] stack backtrace:
> [    0.952660] Pid: 1, comm: swapper Not tainted 3.5.0-01540-g1669891 #64
> [    0.954364] Call Trace:
> [    0.955074]  [<ffffffff8108b375>] lockdep_rcu_suspicious+0x174/0x187
> [    0.956736]  [<ffffffff822c7453>] xfrm_net_init+0x30e/0x437
> [    0.958205]  [<ffffffff822c7329>] ? xfrm_net_init+0x1e4/0x437
> [    0.959712]  [<ffffffff814e134a>] ops_init+0x1bb/0x1ff
> [    0.961067]  [<ffffffff810861f9>] ? trace_hardirqs_on+0x1b/0x24
> [    0.962644]  [<ffffffff814e17cd>] register_pernet_operations.isra.5+0x9d/0xfe
> [    0.971376]  [<ffffffff814e1adf>] register_pernet_subsys+0x30/0x57
> [    0.972992]  [<ffffffff822c7130>] xfrm_init+0x17/0x2c
> [    0.974316]  [<ffffffff822c2f8c>] ip_rt_init+0x82/0xe7
> [    0.975668]  [<ffffffff822c31dc>] ip_init+0x10/0x25
> [    0.976952]  [<ffffffff822c3f77>] inet_init+0x235/0x360
> [    0.978352]  [<ffffffff822c3d42>] ? devinet_init+0xf2/0xf2
> [    0.979808]  [<ffffffff82283252>] do_one_initcall+0xb4/0x203
> [    0.981313]  [<ffffffff8228354a>] kernel_init+0x1a9/0x29a
> [    0.982732]  [<ffffffff822826d9>] ? loglevel+0x46/0x46
> [    0.990889]  [<ffffffff816d3d84>] kernel_thread_helper+0x4/0x10
> [    0.992472]  [<ffffffff816d262c>] ? retint_restore_args+0x13/0x13
> [    0.994076]  [<ffffffff822833a1>] ? do_one_initcall+0x203/0x203
> [    0.995636]  [<ffffffff816d3d80>] ? gs_change+0x13/0x13
> [    0.997197] TCP established hash table entries: 8192 (order: 5, 131072 bytes)
> [    1.000074] TCP bind hash table entries: 8192 (order: 7, 655360 bytes)
>
> Thanks,
> Fengguang

-- 

Love each day!
--fan