linux-kernel - Re: [PATCH 02/13] bluetooth: hci

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Date:	Thu, 24 Apr 2014 11:01:07 +0200
From:	Andreas Bießmann <andreas@...ssmann.de>
To:	Felipe Balbi <balbi@...com>
Cc:	Greg KH <gregkh@...uxfoundation.org>, marcel@...tmann.org,
	gustavo@...ovan.org, johan.hedberg@...il.com, jslaby@...e.cz,
	grant.likely@...aro.org,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-bluetooth@...r.kernel.org, linux-serial@...r.kernel.org,
	devicetree@...r.kernel.org,
	Linux OMAP Mailing List <linux-omap@...r.kernel.org>,
	Tony Lindgren <tony@...mide.com>
Subject: Re: [PATCH 02/13] bluetooth: hci_ldisc: fix deadlock condition

Dear Felipe Balbi,

On Wed, Apr 23, 2014 at 09:58:26AM -0500, Felipe Balbi wrote:
> LDISCs shouldn't call tty->ops->write() from within
> ->write_wakeup().
> 
> ->write_wakeup() is called with port lock taken and
> IRQs disabled, tty->ops->write() will try to acquire
> the same port lock and we will deadlock.
> 
> Acked-by: Marcel Holtmann <marcel@...tmann.org>
> Reviewed-by: Peter Hurley <peter@...leysoftware.com>
> Reported-by: Huang Shijie <b32955@...escale.com>
> Signed-off-by: Felipe Balbi <balbi@...com>

Tested-by: Andreas Bießmann <andreas@...ssmann.de>

on custom TI AM37xx board with 3.4.87. Therefore I vote for adding this to
stable branches (at least 3.4). It applies with a slight line shifting
(init_work is not available there).

I wonder if you have seen my approach [1] to fix this deadlock.  This stuff is
quiet new to me. As I understood the work_queue has a bit more overhead than a
tasklet. Therefore I implemented my fix with a tasklet. Would be great if one
could shed some light on that.

Best regards

Andreas Bießmann

[1] https://lkml.org/lkml/2014/4/16/425

> ---
>  drivers/bluetooth/hci_ldisc.c | 24 +++++++++++++++++++-----
>  drivers/bluetooth/hci_uart.h  |  1 +
>  2 files changed, 20 insertions(+), 5 deletions(-)
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