On Tue, 20 May 2008 12:01:34 +0200 Mariusz Kozlowski <m.kozlowski@tuxland.pl> wrote:

quoted text
> Hello,
> 
> 	This lockdep warning is seen when I remove pcmcia wifi card
> from the slot. Doesn't happen every time. It's x86_32.
> 
> =======================================================
> [ INFO: possible circular locking dependency detected ]
> 2.6.26-rc2-mm1 #2
> -------------------------------------------------------
> pccardd/1037 is trying to acquire lock:
>  (rtnl_mutex){--..}, at: [<c02870f1>] rtnl_lock+0x14/0x16
> 
> but task is already holding lock:
>  (&socket->skt_mutex){--..}, at: [<c02608ba>] pccardd+0x161/0x28c
> 
> which lock already depends on the new lock.
> 
> 
> the existing dependency chain (in reverse order) is:

OK, three locks are involved here.

quoted text
> -> #2 (&socket->skt_mutex){--..}:
>        [<c013fff0>] __lock_acquire+0xf3b/0x103b
>        [<c0140169>] lock_acquire+0x79/0x92
>        [<c02cfcd5>] mutex_lock_nested+0x90/0x290
>        [<c02600a6>] pccard_register_pcmcia+0x22/0x78
>        [<ded5af02>] pcmcia_bus_add_socket+0x9f/0xe0 [pcmcia]
>        [<c0251c02>] class_interface_register+0x83/0xb2
>        [<ded6003a>] 0xded6003a
>        [<c0146115>] sys_init_module+0x11e/0x18e4
>        [<c0103001>] sysenter_past_esp+0x6a/0xa5
>        [<ffffffff>] 0xffffffff

	cls->mutex
	  socket->skt_mutex

quoted text
> -> #1 (&cls->mutex){--..}:
>        [<c013fff0>] __lock_acquire+0xf3b/0x103b
>        [<c0140169>] lock_acquire+0x79/0x92
>        [<c02cfcd5>] mutex_lock_nested+0x90/0x290
>        [<c024f4a0>] device_add+0x42f/0x557
>        [<c02895a1>] netdev_register_kobject+0x76/0x7b
>        [<c027e3f6>] register_netdevice+0x22e/0x39a
>        [<c027e599>] register_netdev+0x37/0x44
>        [<c03ce7fb>] loopback_net_init+0x38/0x7d
>        [<c027bb59>] register_pernet_operations+0x18/0x1a
>        [<c027bbd3>] register_pernet_device+0x24/0x51
>        [<c03ce7c1>] loopback_init+0x12/0x14
>        [<c03b9721>] kernel_init+0x80/0x227
>        [<c0103c13>] kernel_thread_helper+0x7/0x10
>        [<ffffffff>] 0xffffffff

	rtnl_lock
	  cls->mutex

quoted text
> -> #0 (rtnl_mutex){--..}:
>        [<c013fb8e>] __lock_acquire+0xad9/0x103b
>        [<c0140169>] lock_acquire+0x79/0x92
>        [<c02cfcd5>] mutex_lock_nested+0x90/0x290
>        [<c02870f1>] rtnl_lock+0x14/0x16
>        [<c027e04d>] unregister_netdev+0x10/0x1f
>        [<ded9d11f>] orinoco_cs_detach+0x20/0x32 [orinoco_cs]
>        [<ded5775a>] pcmcia_device_remove+0x3c/0xcf [pcmcia]
>        [<c0250efe>] __device_release_driver+0x5e/0x84
>        [<c0250fe2>] device_release_driver+0x20/0x2b
>        [<c0250434>] bus_remove_device+0x73/0x8b
>        [<c024ef95>] device_del+0xdb/0x14b
>        [<c024f015>] device_unregister+0x10/0x1a
>        [<ded5768e>] pcmcia_card_remove+0x76/0x8c [pcmcia]
>        [<ded5825d>] ds_event+0x59/0x9e [pcmcia]
>        [<c025ffa6>] send_event+0x7c/0xa8
>        [<c02601da>] socket_remove_drivers+0x17/0x19
>        [<c02601ef>] socket_shutdown+0x13/0xcc
>        [<c02602d3>] socket_remove+0x2b/0x31
>        [<c026098f>] pccardd+0x236/0x28c
>        [<c01318bb>] kthread+0x3b/0x5d
>        [<c0103c13>] kernel_thread_helper+0x7/0x10
>        [<ffffffff>] 0xffffffff

	cls->mutex
	  rtnl_lock

quoted text
> other info that might help us debug this:
> 
> 1 lock held by pccardd/1037:
>  #0:  (&socket->skt_mutex){--..}, at: [<c02608ba>] pccardd+0x161/0x28c
> 
> stack backtrace:
> Pid: 1037, comm: pccardd Not tainted 2.6.26-rc2-mm1 #2
>  [<c013d8d6>] print_circular_bug_tail+0x68/0x71
>  [<c013cfd5>] ? print_circular_bug_entry+0x43/0x4b
>  [<c013fb8e>] __lock_acquire+0xad9/0x103b
>  [<c013f42f>] ? __lock_acquire+0x37a/0x103b
>  [<c013f42f>] ? __lock_acquire+0x37a/0x103b
>  [<c0108587>] ? native_sched_clock+0x66/0xaf
>  [<c0140169>] lock_acquire+0x79/0x92
>  [<c02870f1>] ? rtnl_lock+0x14/0x16
>  [<c02cfcd5>] mutex_lock_nested+0x90/0x290
>  [<c02870f1>] ? rtnl_lock+0x14/0x16
>  [<c02870f1>] ? rtnl_lock+0x14/0x16
>  [<c02870f1>] rtnl_lock+0x14/0x16
>  [<c027e04d>] unregister_netdev+0x10/0x1f
>  [<ded9d11f>] orinoco_cs_detach+0x20/0x32 [orinoco_cs]
>  [<ded5775a>] pcmcia_device_remove+0x3c/0xcf [pcmcia]
>  [<c0250efe>] __device_release_driver+0x5e/0x84
>  [<c0250fe2>] device_release_driver+0x20/0x2b
>  [<c0250434>] bus_remove_device+0x73/0x8b
>  [<c024ef95>] device_del+0xdb/0x14b
>  [<c024f015>] device_unregister+0x10/0x1a
>  [<ded5768e>] pcmcia_card_remove+0x76/0x8c [pcmcia]
>  [<ded5825d>] ds_event+0x59/0x9e [pcmcia]
>  [<c02601da>] ? socket_remove_drivers+0x17/0x19
>  [<c025ffa6>] send_event+0x7c/0xa8
>  [<c02601da>] socket_remove_drivers+0x17/0x19
>  [<c02601ef>] socket_shutdown+0x13/0xcc
>  [<c0120d15>] ? printk+0x20/0x22
>  [<c02602d3>] socket_remove+0x2b/0x31
>  [<c026098f>] pccardd+0x236/0x28c
>  [<c02cf0e8>] ? schedule+0x2c4/0x46f
>  [<c011b3eb>] ? sub_preempt_count+0x76/0xbd
>  [<c011b15f>] ? default_wake_function+0x0/0x12
>  [<c0260759>] ? pccardd+0x0/0x28c
>  [<c01318bb>] kthread+0x3b/0x5d
>  [<c0131880>] ? kthread+0x0/0x5d
>  [<c0103c13>] kernel_thread_helper+0x7/0x10

This bug has always been there, and is now exposed by the conversion
of cls->mutex from a semaphore to a mutex.  Because lockdep doesn't
check semaphores.

I don't know how to get this fixed, sorry.  I'll just push
struct-class-sem-to-mutex-converting.patch at Greg until it sticks,
then it will go into mainline, then we'll get a shower of bug reports,
including this one, then someone someday will do soemthing about it.

Fun.
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