linux-kernel - Re: [PATCH 04/24] tty: Fix ref counting for port krefs

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Message-ID: <20140213183616.GA13509@kroah.com>
Date:	Thu, 13 Feb 2014 10:36:16 -0800
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	Peter Hurley <peter@...leysoftware.com>
Cc:	Marcel Holtmann <marcel@...tmann.org>,
	Gustavo Padovan <gustavo@...ovan.org>,
	Johan Hedberg <johan.hedberg@...il.com>,
	Gianluca Anzolin <gianluca@...tospazio.it>,
	Alexander Holler <holler@...oftware.de>,
	Andrey Vihrov <andrey.vihrov@...il.com>,
	Sander Eikelenboom <linux@...elenboom.it>,
	linux-bluetooth@...r.kernel.org, linux-kernel@...r.kernel.org,
	Jiri Slaby <jslaby@...e.cz>
Subject: Re: [PATCH 04/24] tty: Fix ref counting for port krefs

On Sun, Feb 09, 2014 at 08:59:04PM -0500, Peter Hurley wrote:
> The tty core supports two models for handling tty_port lifetimes;
> the tty_port can use the kref supplied by tty_port (which will
> automatically destruct the tty_port when the ref count drops to
> zero) or it can destruct the tty_port manually.
> 
> For tty drivers that choose to use the port kref to manage the
> tty_port lifetime, it is not possible to safely acquire a port
> reference conditionally. If the last reference is released after
> evaluating the condition but before acquiring the reference, a
> bogus reference will be held while the tty_port destruction
> commences.
> 
> Rather, only acquire a port reference if the ref count is non-zero
> and allow the caller to distinguish if a reference has successfully
> been acquired.
> 
> Cc: Jiri Slaby <jslaby@...e.cz>
> Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> Signed-off-by: Peter Hurley <peter@...leysoftware.com>

Acked-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

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