linux-kernel - Re: [PATCH 1/1] ser_gigaset: use container

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Message-ID: <56C63AB7.9060401@imap.cc>
Date:	Thu, 18 Feb 2016 22:42:15 +0100
From:	Tilman Schmidt <tilman@...p.cc>
To:	Paul Bolle <pebolle@...cali.nl>, netdev@...r.kernel.org
Cc:	Dmitry Vyukov <dvyukov@...gle.com>,
	Uwe Kleine-König <u.kleine-koenig@...gutronix.de>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Martin Wilck <Martin.Wilck@...fujitsu.com>,
	Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>,
	linux-kernel@...r.kernel.org,
	gigaset307x-common@...ts.sourceforge.net
Subject: Re: [PATCH 1/1] ser_gigaset: use container_of() instead of detour

Am 18.02.2016 um 21:29 schrieb Paul Bolle:
> The purpose of gigaset_device_release() is to kfree() the struct
> ser_cardstate that contains our struct device. This is done via a bit of
> a detour. First we make our struct device's driver_data point to the
> container of our struct ser_cardstate (which is a struct cardstate). In
> gigaset_device_release() we then retrieve that driver_data again. And
> after that we finally kfree() the struct ser_cardstate that was saved in
> the struct cardstate.
> 
> All of this can be achieved much easier by using container_of() to get
> from our struct device to its container, struct ser_cardstate. Do so.

You're absolutely right. Very nice!

> Note that at the time the detour was implemented commit b8b2c7d845d5
> ("base/platform: assert that dev_pm_domain callbacks are called
> unconditionally") had just entered the tree. That commit disconnected
> our platform_device and our platform_driver. These were reconnected
> again in v4.5-rc2 through commit 25cad69f21f5 ("base/platform: Fix
> platform drivers with no probe callback"). And one of the consequences
> of that fix was that it broke the detour via driver_data. That's because
> it made __device_release_driver() stop being a NOP for our struct device
> and actually do stuff again. One of the things it now does, is setting
> our driver_data to NULL. That, in turn, makes it impossible for
> gigaset_device_release() to get to our struct cardstate. Which has the
> net effect of leaking a struct ser_cardstate at every call of this
> driver's tty close() operation. So using container_of() has the
> additional benefit of actually working.
> 
> Reported-by: Dmitry Vyukov <dvyukov@...gle.com>
> Tested-by: Dmitry Vyukov <dvyukov@...gle.com>
> Signed-off-by: Paul Bolle <pebolle@...cali.nl>

Acked-by: Tilman Schmidt <tilman@...p.cc>

Thanks for cleaning up the mess I left behind.

Tilman

-- 
Tilman Schmidt                              E-Mail: tilman@...p.cc
Bonn, Germany
Nous, on a des fleurs et des bougies pour nous protéger.


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