linux-kernel - Re: bluetooth: fix deadlock on device reset and power down

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Message-ID: <20120402090337.GB29687@aemeltch-MOBL1>
Date:	Mon, 2 Apr 2012 12:03:46 +0300
From:	Andrei Emeltchenko <andrei.emeltchenko.news@...il.com>
To:	David Herrmann <dh.herrmann@...glemail.com>
Cc:	Alexander Holler <holler@...oftware.de>,
	linux-bluetooth@...r.kernel.org, linux-kernel@...r.kernel.org,
	"Gustavo F. Padovan" <padovan@...fusion.mobi>
Subject: Re: bluetooth: fix deadlock on device reset and power down

Hi guys,

On Mon, Apr 02, 2012 at 10:44:43AM +0200, David Herrmann wrote:
> Hi Andrei and Alexander
> 
> On Mon, Apr 2, 2012 at 10:29 AM, Alexander Holler <holler@...oftware.de> wrote:
> > Am 02.04.2012 08:55, schrieb Andrei Emeltchenko:
> >> Hi Alexander,
> >>
> >> On Sat, Mar 31, 2012 at 03:23:38PM +0200, Alexander Holler wrote:
> >>> I've experienced a deadlock on shutdown using kernel 3.3 and tracked
> >>> it down. Because I'm not very familiar with the bluetooth stack I'm
> >>> not sure if the below patch is correct, but it fixed the problem
> >>> here.
> >>
> >> Could you please attach deadlock dump?
> >>
> >>>
> >>> Commit 09fd0de5bd8f8ef3317e5365f92f1a13dcd89aa9 introduced a deadlock:
> >>>
> >>> bluetoothd calls ioctl HCIDEVDOWN
> >>>     hci_sock_ioctl()
> >>>         hci_dev_close()
> >>>             hci_dev_do_close()
> >>>                 hci_dev_lock(hdev);
> >>>                 inquiry_cache_flush();
> >>>                 hci_conn_hash_flush();
> >>>                     hci_conn_del()
> >>>                         cancel_delayed_work_sync()
> >>>                             hci_conn_timeout()
> >>>                                 hci_dev_lock(hdev); /* DEADLOCK */
> >>
> >> I am actually not sure that hci_conn_timeout locks hdev. Why do you think
> >> so?
> >
> > By reading the source, printk and suffering through the deadlock. It's
> > especially painfull when using a bt-keyboard and systemd, because
> > systemd tries 4 times (~ some minutes) to kill bluetoothd before it
> > marks the service as failed and finally continues to shut down.
> 
> hci_conn_timeout does lock the device. See the source. But the problem

I think you need to check commit e72acc13c770a82b4ce4a07e9716f29320eae0f8

commit e72acc13c770a82b4ce4a07e9716f29320eae0f8
Author: Andre Guedes <andre.guedes@...nbossa.org>
Date:   Fri Jan 27 19:42:03 2012 -0300

    Bluetooth: Remove unneeded locking
    
    We don't need locking hdev in hci_conn_timeout() since it doesn't
    access any hdev's shared resources, it basically queues HCI commands.

Best regards 
Andrei Emeltchenko 

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