Return-Path: <cyrus@holtmann.org>
Date: Mon, 2 Apr 2012 12:03:46 +0300
From: Andrei Emeltchenko <andrei.emeltchenko.news@gmail.com>
To: David Herrmann <dh.herrmann@googlemail.com>
Cc: Alexander Holler <holler@ahsoftware.de>,
	linux-bluetooth@vger.kernel.org, linux-kernel@vger.kernel.org,
	"Gustavo F. Padovan" <padovan@profusion.mobi>
Subject: Re: bluetooth: fix deadlock on device reset and power down
Message-ID: <20120402090337.GB29687@aemeltch-MOBL1>
References: <4F77055A.2070502@ahsoftware.de>
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 <4F796377.2050008@ahsoftware.de>
 <CANq1E4RCQvQX6deGOTjdhbEkAahZD9MmAmfgz-Y-+wDfRtx0dw@mail.gmail.com>
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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@ahsoftware.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@openbossa.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