linux-kernel - Re: [PATCH] tty: Prevent deadlock in n

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Date:	Wed, 30 Jan 2013 11:10:58 +0100
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	Dirkjan Bussink <dirkjan.bussink@...ap.com>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] tty: Prevent deadlock in n_gsm driver

On Wed, Jan 30, 2013 at 10:51:59AM +0100, Dirkjan Bussink wrote:
> This change fixes a deadlock when the multiplexer is closed while there
> are still client side ports open.
> 
> When the multiplexer is closed and there are active tty's it tries to
> close them with tty_vhangup. This has a problem though, because
> tty_vhangup needs the tty_lock. This patch changes it to unlock the
> tty_lock before attempting the hangup and relocks afterwards. The
> additional call to tty_port_tty_set is needed because otherwise the
> port stays active because of the reference counter.
> 
> This change also exposed another problem that other code paths don't
> expect that the multiplexer could have been closed. This patch also adds
> checks for these cases in the gsmtty_ class of function that could be
> called.
> 
> The documentation explicitly states that "first close all virtual ports
> before closing the physical port" but we've found this to not always
> reality in our field situations. The GPRS / UTMS modem sometimes crashes
> and needs a power cycle in that case which means cleanly shutting down
> everything is not always possible. This change makes it much more robust
> for our situation where at least the system is recoverable with this patch
> and doesn't hang in a deadlock situation inside the kernel.
> 
> The patch is against the long term support kernel (3.4.27) and should
> apply cleanly to more recent branches. Tested with a Telit GE864-QUADV2
> and Telit HE910 modem.
> 
> Signed-off-by: Dirkjan Bussink <dirkjan.bussink@...ap.com>
> Cc: stable <stable@...r.kernel.org>

This patch breaks the build in the tty-next tree:

drivers/tty/n_gsm.c: In function ‘gsm_dlci_release’:
drivers/tty/n_gsm.c:1713:3: error: too few arguments to function ‘tty_unlock’
In file included from drivers/tty/n_gsm.c:44:0:
include/linux/tty.h:596:24: note: declared here
drivers/tty/n_gsm.c:1715:3: error: too few arguments to function ‘tty_lock’
In file included from drivers/tty/n_gsm.c:44:0:
include/linux/tty.h:595:24: note: declared here

Can you fix this up (get it to build on the linux-next tree) and resend
it?

thanks,

greg k-h
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