Re: [PATCH 02/13] bluetooth: hci_ldisc: fix deadlock condition

[Andreas Bießmann]

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@xxxxxxxxxxxx>
> Reviewed-by: Peter Hurley <peter@xxxxxxxxxxxxxxxxxx>
> Reported-by: Huang Shijie <b32955@xxxxxxxxxxxxx>
> Signed-off-by: Felipe Balbi <balbi@xxxxxx>

Tested-by: Andreas Bießmann <andreas@xxxxxxxxxxxx>

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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