netdev - Possible locking problem with register

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Date:	Thu, 17 Jul 2008 02:21:41 +0200
From:	Frédéric Weisbecker <fweisbec@...il.com>
To:	linux-next@...r.kernel.org
CC:	netdev@...r.kernel.org
Subject: Possible locking problem with register_netdev

Hi,

On each boot I get a locking alert during loopback device init.
I'm not sure if it's really a bug and where is the origin of that.

Here is the message and my .config in attachment.

 =============================================
 [ INFO: possible recursive locking detected ]
 2.6.26-next-20080716 #5
 --------------------------------------------
 swapper/1 is trying to acquire lock:
  (&queue->lock){-...}, at: [inet_twsk_alloc+195/256] 
qdisc_lock_tree+0x23/0x30

 but task is already holding lock:
  (&queue->lock){-...}, at: [inet_twsk_alloc+188/256] 
qdisc_lock_tree+0x1c/0x30

 other info that might help us debug this:
 3 locks held by swapper/1:
  #0:  (net_mutex){--..}, at: [netlink_insert+288/304] 
register_pernet_device+0x20/0x60
  #1:  (rtnl_mutex){--..}, at: [ip_finish_output+308/736] 
rtnl_lock+0x14/0x20
  #2:  (&queue->lock){-...}, at: [inet_twsk_alloc+188/256] 
qdisc_lock_tree+0x1c/0x30

 stack backtrace:
 Pid: 1, comm: swapper Not tainted 2.6.26-next-20080716 #5
  [sys_init_module+3779/7568] __lock_acquire+0xf23/0x1160
  [sys_init_module+4481/7568] lock_acquire+0x81/0xa0
  [inet_twsk_alloc+195/256] ? qdisc_lock_tree+0x23/0x30
  [proc_sysrq_trigger_operations+45/108] _spin_lock+0x3d/0x70
  [inet_twsk_alloc+195/256] ? qdisc_lock_tree+0x23/0x30
  [inet_twsk_alloc+195/256] qdisc_lock_tree+0x23/0x30
  [inet_twsk_put+16/112] dev_init_scheduler+0x10/0x50
  [genl_ctrl_event+710/800] register_netdevice+0x1d6/0x330
  [math_state_restore+75/112] ? mcount_call+0x5/0xa
  [genl_unregister_family+239/256] register_netdev+0x3f/0x60
  [empty_zero_page+2750/4096] loopback_net_init+0x3e/0x80
  [netlink_insert+152/304] register_pernet_operations+0x18/0x20
  [netlink_insert+300/304] register_pernet_device+0x2c/0x60
  [empty_zero_page+2674/4096] loopback_init+0x12/0x20
  [rtnetlink_init+42/304] kernel_init+0x10a/0x2e0
  [sysfs_dir_operations+18/128] ? _spin_unlock_irq+0x32/0x50
  [empty_zero_page+2656/4096] ? loopback_init+0x0/0x20
  [show_modinfo_version+23/48] ? trace_hardirqs_on_caller+0xc7/0x150
  [pci_find_slot+76/80] ? trace_hardirqs_on_thunk+0xc/0x10
  [work_notifysig_v86+14/24] ? restore_nocheck_notrace+0x0/0xe
  [dev_mc_net_init+0/48] ? kernel_init+0x0/0x2e0
  [dev_mc_net_init+0/48] ? kernel_init+0x0/0x2e0
  [math_state_restore+51/112] kernel_thread_helper+0x7/0x10
 =======================

View attachment "config" of type "text/plain" (48573 bytes)