Re: [RFC 0/4] clk/driver: platform: Fix kfree() of const memory on setting driver_override

From: Stephen Boyd <sboyd@kernel.org>
To: Geert Uytterhoeven <geert@linux-m68k.org>,
	Krzysztof Kozlowski <krzk@kernel.org>
Cc: Russell King <linux@armlinux.org.uk>,
	Mark Brown <broonie@kernel.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	linux-spi <linux-spi@vger.kernel.org>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	"Rafael J. Wysocki" <rafael@kernel.org>,
	Sylwester Nawrocki <s.nawrocki@samsung.com>,
	Tomasz Figa <tomasz.figa@gmail.com>,
	Chanwoo Choi <cw00.choi@samsung.com>,
	Michael Turquette <mturquette@baylibre.com>,
	Kukjin Kim <kgene@kernel.org>, Andy Gross <andy.gross@linaro.org>,
	David Brown <david.brown@linaro.org>,
	Srinivas Kandagatla <srinivas.kandagatla@linaro.org>,
	"linux-samsung-soc@vger.kernel.org"
	<linux-samsung-soc@vger.kernel.org>,
	linux-clk <linux-clk@vger.kernel.org>,
	Linux ARM <linux-arm-kernel@lists.infradead.org>,
	linux-a
Subject: Re: [RFC 0/4] clk/driver: platform: Fix kfree() of const memory on setting driver_override
Date: Wed, 20 Feb 2019 14:01:42 -0800	[thread overview]
Message-ID: <155070010208.77512.17397936280518534534@swboyd.mtv.corp.google.com> (raw)
In-Reply-To: <CAJKOXPe1CW4k4ivbh4QhKEbuVc3RRNmzUwQcL0BsrAn=hCdjZg@mail.gmail.com>

Quoting Krzysztof Kozlowski (2019-02-18 03:14:29)
> On Mon, 18 Feb 2019 at 11:40, Geert Uytterhoeven <geert@linux-m68k.org> wrote:
> >
> > Hi Krzysztof,
> >
> > On Mon, Feb 18, 2019 at 11:27 AM Krzysztof Kozlowski <krzk@kernel.org> wrote:
> > > The problem
> > > ===========
> > > Several device types (platform, amba, spi etc.) provide a driver_override
> > > field.  On sysfs store or during device removal, they kfree() the
> > > existing value.
> > >
> > > However the users are unaware of this and set the driver_override like:
> > >
> > >         pdev->driver_override = "exynos5-subcmu";
> > >
> > > which obviously leads to error.
> >
> > IMHO driver_override is not meant to be set by a driver, only from userspace,
> > for binding the device to vfio (is there another use case?).
> >
> > >   clk: samsung: exynos5: Fix kfree() of const memory on setting
> > >     driver_override
> > >   slimbus: ngd: Fix kfree() of const memory on setting driver_override
> >
> > I see all users set override immediately after allocating a platform device.
> > Can't they just allocate a platform device using the override name instead?
> > What am I missing?
> 
> For the clk-exynos5-subcmu.c case, driver registers several
> sub-devices. Each sub-devices is a clock controller associated with
> power domain. I guess the author wanted to have meaningful names of
> these sub-devices (DISP, CAM etc. like names of power domains),
> instead of just exynos5-subcmu.1, exynos5-subcmu.2 ...
> 
> If driver_override should not be used for such case, then I could
> replace it with what you said.

Looking at the introduction of the code into the platform bus makes it
sound like it was all for vfio devices. If the clk driver doesn't need
it for that purpose and can get by with more generic names then it seems
best to avoid using it entirely. So can you do that and resend the first
patch in this series too? Effectively splitting the clk parts from the
larger issue of kfree()ing of const memory.