Subject: suspicious RCU usage in xfrm_net_init()

From: Fengguang Wu <[email-masked]>
Date: Thu, 16 Aug 2012 15:37:24 +0800

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