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Date: Tue, 11 Nov 2008 12:07:08 +0100
From: Ingo Molnar <mingo@elte.hu>
To: Oleg Nesterov <oleg@redhat.com>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>,
       "Rafael J. Wysocki" <rjw@sisk.pl>,
       Dmitry Torokhov <dmitry.torokhov@gmail.com>,
       Dmitry Adamushko <dmitry.adamushko@gmail.com>,
       Max Krasnyansky <maxk@qualcomm.com>,
       Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
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Subject: Re: [Bug #11380] lockdep warning: cpu_add_remove_lock
	at:cpu_maps_update_begin+0x14/0x16
Message-ID: <20081111110708.GE15645@elte.hu>
References: <20081110073047.GA28578@elte.hu> <20081110132208.GB10294@redhat.com> <20081111105706.6174.KOSAKI.MOTOHIRO@jp.fujitsu.com> <20081111120111.GA3503@redhat.com>
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* Oleg Nesterov <oleg@redhat.com> wrote:

> On 11/11, KOSAKI Motohiro wrote:
> >
> > it seem simple ABBA lock, right?
> >
> > -> #4 (&dev->mutex){--..}:
> >        [<c0160f87>] validate_chain+0x831/0xaa2
> >        [<c0161872>] __lock_acquire+0x67a/0x6e0
> >        [<c0161933>] lock_acquire+0x5b/0x81
> >        [<c0a660e4>] mutex_lock_interruptible_nested+0xde/0x2f8
> >        [<c0782d02>] input_register_handle+0x26/0x7a			dev->mutex
>                                                                         ^^^^^^^^^^
> >        [<c04a62c9>] kbd_connect+0x64/0x8d
> >        [<c0782842>] input_attach_handler+0x38/0x6b
> >        [<c0784216>] input_register_handler+0x74/0xc3			input_mutex
> >        [<c0f54e4b>] kbd_init+0x66/0x91
> >        [<c0f54f7b>] vty_init+0xce/0xd7
> >        [<c0f54952>] tty_init+0x193/0x197
> >        [<c010112a>] do_one_initcall+0x42/0x133
> >        [<c0f2d5cb>] kernel_init+0x16e/0x1d5
> >        [<c0117c03>] kernel_thread_helper+0x7/0x10
> >        [<ffffffff>] 0xffffffff
> >
> > -> #3 (input_mutex){--..}:
> >        [<c0160f87>] validate_chain+0x831/0xaa2
> >        [<c0161872>] __lock_acquire+0x67a/0x6e0
> >        [<c0161933>] lock_acquire+0x5b/0x81
> >        [<c0a660e4>] mutex_lock_interruptible_nested+0xde/0x2f8
> >        [<c0783fbe>] input_register_device+0xff/0x17f		input_mutex
> >        [<c048a889>] acpi_button_add+0x31e/0x429
> >        [<c04889f4>] acpi_device_probe+0x43/0xde
> >        [<c052c67f>] driver_probe_device+0xa5/0x120
> >        [<c052c73c>] __driver_attach+0x42/0x64			dev->sem
>                                                                 ^^^^^^^^
> input_dev->mutex != device->sem
> 
> > ...
> >        [<c0f2d201>] do_async_initcalls+0x1a/0x2a
> >        [<c0150eec>] run_workqueue+0xc3/0x193			
> >        [<c015195d>] worker_thread+0xbb/0xc7
> >        [<c0153e2a>] kthread+0x40/0x66
> 
> What is the kernel version, btw? I can't find do_async_initcalls
> in 2.6.27 or 2.6.28.

i suspect it's an older version of tip/master that still had async 
initcalls.

> Anyway, this really looks like lockdep bug to me. Even if we really 
> have the circular dependency (will try to grep more) I can't 
> understand why lockdep claims that polldev_mutex depends on 
> cpu_add_remove_lock.

ok, will re-report if i can trigger it again with latest kernels. 
Rafael, please close this bug as cannot-reproduce for now.

	Ingo
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