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    SubjectRe: i2c_powermac: Kernel access of bad area
    Hi Christian, hi Ben,

    On Tue, 29 Dec 2009 20:34:15 +1100, Benjamin Herrenschmidt wrote:
    > On Mon, 2009-12-28 at 20:40 -0800, Christian Kujau wrote:
    > > Hi there,
    > >
    > > I was trying to find out if I still need i2c_powermac to get details off
    > > /sys/devices/temperatures, since lm-sensors isn't working for me anyway.

    This is because the macintosh/therm_adt746x driver doesn't follow the
    standard hwmon sysfs interface. I would love to see that change.

    > > After unloading this module, I noticed that reading certain objects would
    > > fail with a segfault on the prompt and an Oops in the kernel log:
    > Definitely looks like we fail to clean things up on remove.


    > I don't have much time to look into this right now, so best is you file
    > a bug report on, make sure I'm CCed.
    > Jean (added on CC), in case you already know what's up, please share :-)

    I don't know anything about this for now. But I'll help if I can.

    Christian, did you happen to try removing the i2c-powermac driver
    before? I am curious if this is a recent problem, possibly caused by
    changes to the i2c stack, or if older kernels already had this problem
    and nobody ever noticed. I suspect the latter.

    Looking at drivers/macintosh/therm_adt746x.c, the sysfs files are
    created in thermostat_init() and removed in thermostat_exit(), which
    are the driver's init and exit functions. These files are backed-up by
    a per-device structure, so it looks like the wrong thing to do. I think
    this is the problem: the sysfs files have a lifetime longer than the
    data structure that is backing it up. This is somewhat different from
    "we fail to clean things up on remove": I suspect that even if
    i2c-powermac was never ever loaded, the same problem would happen.

    I think that sysfs files creation should be moved to the end of
    probe_thermostat() and sysfs files removal should be moved to the
    beginning of remove_thermostat(). Something like the totally untested
    patch below (no ppc machine at hand):

    drivers/macintosh/therm_adt746x.c | 34 ++++++++++++++++++++++++----------
    1 file changed, 24 insertions(+), 10 deletions(-)

    --- linux-2.6.33-rc3.orig/drivers/macintosh/therm_adt746x.c 2010-01-06 17:30:48.000000000 +0100
    +++ linux-2.6.33-rc3/drivers/macintosh/therm_adt746x.c 2010-01-06 17:36:35.000000000 +0100
    @@ -90,6 +90,8 @@ static struct task_struct *thread_therm

    static void write_both_fan_speed(struct thermostat *th, int speed);
    static void write_fan_speed(struct thermostat *th, int speed, int fan);
    +static void thermostat_create_files(void);
    +static void thermostat_remove_files(void);

    static int
    write_reg(struct thermostat* th, int reg, u8 data)
    @@ -161,6 +163,8 @@ remove_thermostat(struct i2c_client *cli
    struct thermostat *th = i2c_get_clientdata(client);
    int i;

    + thermostat_remove_files();
    if (thread_therm != NULL) {
    @@ -449,6 +453,8 @@ static int probe_thermostat(struct i2c_c
    return -ENOMEM;

    + thermostat_create_files();
    return 0;

    @@ -566,7 +572,6 @@ thermostat_init(void)
    struct device_node* np;
    const u32 *prop;
    int i = 0, offset = 0;
    - int err;

    np = of_find_node_by_name(NULL, "fan");
    if (!np)
    @@ -633,6 +638,17 @@ thermostat_init(void)
    return -ENODEV;

    +#ifndef CONFIG_I2C_POWERMAC
    + request_module("i2c-powermac");
    + return i2c_add_driver(&thermostat_driver);
    +static void thermostat_create_files(void)
    + int err;
    err = device_create_file(&of_dev->dev, &dev_attr_sensor1_temperature);
    err |= device_create_file(&of_dev->dev, &dev_attr_sensor2_temperature);
    err |= device_create_file(&of_dev->dev, &dev_attr_sensor1_limit);
    @@ -647,16 +663,9 @@ thermostat_init(void)
    if (err)
    "Failed to create tempertaure attribute file(s).\n");
    -#ifndef CONFIG_I2C_POWERMAC
    - request_module("i2c-powermac");
    - return i2c_add_driver(&thermostat_driver);

    -static void __exit
    +static void thermostat_remove_files(void)
    if (of_dev) {
    device_remove_file(&of_dev->dev, &dev_attr_sensor1_temperature);
    @@ -673,9 +682,14 @@ thermostat_exit(void)

    - of_device_unregister(of_dev);
    +static void __exit
    + of_device_unregister(of_dev);

    Jean Delvare

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      Last update: 2010-01-06 17:41    [W:0.037 / U:0.352 seconds]
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