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

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Date:	Mon, 2 Apr 2012 09:55:27 +0300
From:	Andrei Emeltchenko <andrei.emeltchenko.news@...il.com>
To:	Alexander Holler <holler@...oftware.de>
Cc:	linux-bluetooth@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: bluetooth: fix deadlock on device reset and power down

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?

Best regards 
Andrei Emeltchenko 

>                 hci_dev_unlock(hdev);
> 
> Signed-off-by: Alexander Holler <holler@...oftware.de>
> ---
>  net/bluetooth/hci_core.c |    4 ++--
>  1 files changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/net/bluetooth/hci_core.c b/net/bluetooth/hci_core.c
> index 5aeb624..3428036 100644
> --- a/net/bluetooth/hci_core.c
> +++ b/net/bluetooth/hci_core.c
> @@ -629,8 +629,8 @@ static int hci_dev_do_close(struct hci_dev *hdev)
> 
>  	hci_dev_lock(hdev);
>  	inquiry_cache_flush(hdev);
> -	hci_conn_hash_flush(hdev);
>  	hci_dev_unlock(hdev);
> +	hci_conn_hash_flush(hdev);
> 
>  	hci_notify(hdev, HCI_DEV_DOWN);
> 
> @@ -713,8 +713,8 @@ int hci_dev_reset(__u16 dev)
> 
>  	hci_dev_lock(hdev);
>  	inquiry_cache_flush(hdev);
> -	hci_conn_hash_flush(hdev);
>  	hci_dev_unlock(hdev);
> +	hci_conn_hash_flush(hdev);
> 
>  	if (hdev->flush)
>  		hdev->flush(hdev);

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