linux-kernel - Re: [PATCH RESEND] spi: erase pointer to drvdata on removal

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Date:	Tue, 4 Dec 2012 14:56:15 +0000
From:	Grant Likely <grant.likely@...retlab.ca>
To:	Vivien Didelot <vivien.didelot@...oirfairelinux.com>
Cc:	spi-devel-general@...ts.sourceforge.net,
	Rob Herring <rob.herring@...xeda.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [PATCH RESEND] spi: erase pointer to drvdata on removal

On Mon, Dec 3, 2012 at 8:28 PM, Vivien Didelot
<vivien.didelot@...oirfairelinux.com> wrote:
> Without this patch, a SPI device may keep its drvdata whereas it was unbound
> from its driver. This may result in accessing an invalid pointer.
>
> As for i2c-core, let the SPI core handle the removal of the device's drvdata,
> after a remove(), or a probe() failure.
>
> This is a resent of the previous patch https://lkml.org/lkml/2012/11/1/314
>
> Signed-off-by: Vivien Didelot <vivien.didelot@...oirfairelinux.com>

Are you seeing a real bug without this patch? If so, then that is a
driver bug. I don't want to mask over bugs silently. The kernel should
complain.

There are actually lots of things that drivers should/should-not do
that could be checked by the probe/remove hooks, and not just in the
SPI code. spi_set_drvdata() is actually just a wrapper around
dev_set_drvdata().

Instead of clearing the pointer only in the spi code, perhaps the
checks should be in really_probe() and __device_release_driver() so it
covers all bus types. Also, don't clear the pointer. Just use
dev_err() to report on the driver bug so that it gets fixed properly.

g.

> ---
>  drivers/spi/spi.c | 14 ++++++++++++--
>  1 file changed, 12 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/spi/spi.c b/drivers/spi/spi.c
> index 84c2861..fe636fe 100644
> --- a/drivers/spi/spi.c
> +++ b/drivers/spi/spi.c
> @@ -233,15 +233,25 @@ EXPORT_SYMBOL_GPL(spi_bus_type);
>  static int spi_drv_probe(struct device *dev)
>  {
>         const struct spi_driver         *sdrv = to_spi_driver(dev->driver);
> +       struct spi_device               *sdev = to_spi_device(dev);
> +       int                             status;
>
> -       return sdrv->probe(to_spi_device(dev));
> +       status = sdrv->probe(sdev);
> +       if (status)
> +               spi_set_drvdata(sdev, NULL);
> +       return status;
>  }
>
>  static int spi_drv_remove(struct device *dev)
>  {
>         const struct spi_driver         *sdrv = to_spi_driver(dev->driver);
> +       struct spi_device               *sdev = to_spi_device(dev);
> +       int                             status;
>
> -       return sdrv->remove(to_spi_device(dev));
> +       status = sdrv->remove(sdev);
> +       if (status == 0)
> +               spi_set_drvdata(sdev, NULL);
> +       return status;
>  }
>
>  static void spi_drv_shutdown(struct device *dev)
> --
> 1.7.11.7
>
> --
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--
Grant Likely, B.Sc., P.Eng.
Secret Lab Technologies Ltd.
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