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    Subject[09/50] hwmon: (max1111) Fix race condition causing NULL pointer exception
    2.6.33-longterm review patch.  If anyone has any objections, please let us know.

    ------------------

    From: Pavel Herrmann <morpheus.ibis@gmail.com>

    commit d3f684f2820a7f42acef68bea6622d9032127fb2 upstream.

    spi_sync call uses its spi_message parameter to keep completion information,
    using a drvdata structure is not thread-safe. Use a mutex to prevent
    multiple access to shared driver data.

    Signed-off-by: Pavel Herrmann <morpheus.ibis@gmail.com>
    Acked-by: Russell King <rmk+kernel@arm.linux.org.uk>
    Acked-by: Pavel Machek <pavel@ucw.cz>
    Acked-by: Marek Vasut <marek.vasut@gmail.com>
    Acked-by: Cyril Hrubis <metan@ucw.cz>
    Tested-by: Stanislav Brabec <utx@penguin.cz>
    Signed-off-by: Jean Delvare <khali@linux-fr.org>
    Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

    ---
    drivers/hwmon/max1111.c | 11 +++++++++++
    1 file changed, 11 insertions(+)

    --- a/drivers/hwmon/max1111.c
    +++ b/drivers/hwmon/max1111.c
    @@ -39,6 +39,8 @@ struct max1111_data {
    struct spi_transfer xfer[2];
    uint8_t *tx_buf;
    uint8_t *rx_buf;
    + struct mutex drvdata_lock;
    + /* protect msg, xfer and buffers from multiple access */
    };

    static int max1111_read(struct device *dev, int channel)
    @@ -47,6 +49,9 @@ static int max1111_read(struct device *d
    uint8_t v1, v2;
    int err;

    + /* writing to drvdata struct is not thread safe, wait on mutex */
    + mutex_lock(&data->drvdata_lock);
    +
    data->tx_buf[0] = (channel << MAX1111_CTRL_SEL_SH) |
    MAX1111_CTRL_PD0 | MAX1111_CTRL_PD1 |
    MAX1111_CTRL_SGL | MAX1111_CTRL_UNI | MAX1111_CTRL_STR;
    @@ -54,12 +59,15 @@ static int max1111_read(struct device *d
    err = spi_sync(data->spi, &data->msg);
    if (err < 0) {
    dev_err(dev, "spi_sync failed with %d\n", err);
    + mutex_unlock(&data->drvdata_lock);
    return err;
    }

    v1 = data->rx_buf[0];
    v2 = data->rx_buf[1];

    + mutex_unlock(&data->drvdata_lock);
    +
    if ((v1 & 0xc0) || (v2 & 0x3f))
    return -EINVAL;

    @@ -175,6 +183,8 @@ static int __devinit max1111_probe(struc
    if (err)
    goto err_free_data;

    + mutex_init(&data->drvdata_lock);
    +
    data->spi = spi;
    spi_set_drvdata(spi, data);

    @@ -212,6 +222,7 @@ static int __devexit max1111_remove(stru

    hwmon_device_unregister(data->hwmon_dev);
    sysfs_remove_group(&spi->dev.kobj, &max1111_attr_group);
    + mutex_destroy(&data->drvdata_lock);
    kfree(data->rx_buf);
    kfree(data->tx_buf);
    kfree(data);



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