Re: [lm-sensors] [patch 1/5] hwmon: Convert fschmd to unlocked_ioctl

[Hans de Goede]

Hi,

On 11/06/2009 02:15 PM, Jean Delvare wrote:
> Hi Thomas,
>
> Sorry for the late answer.
>
> On Thu, 15 Oct 2009 20:28:31 -0000, Thomas Gleixner wrote:
> > The conversion of fschmd watchdog ioctl to unlocked_ioctl needs to
> > protect the static watchdog_info variable for the WDIOC_GETSUPPORT
> > command.
> >
> > All other commands are safe w/o BKL as the called watchdog functions
> > are already serialized with watchdog_lock of the sensor.
> >
> > Signed-off-by: Thomas Gleixner<tglx@xxxxxxxxxxxxx>
> > Cc: lm-sensors@xxxxxxxxxxxxxx
> > ---
> >   drivers/hwmon/fschmd.c |    8 +++++---
> >   1 file changed, 5 insertions(+), 3 deletions(-)
> >
> > Index: linux-2.6-tip/drivers/hwmon/fschmd.c
> > ===================================================================
> > --- linux-2.6-tip.orig/drivers/hwmon/fschmd.c
> > +++ linux-2.6-tip/drivers/hwmon/fschmd.c
> > @@ -844,8 +844,8 @@ static ssize_t watchdog_write(struct fil
> >   	return count;
> >   }
> >
> > -static int watchdog_ioctl(struct inode *inode, struct file *filp,
> > -	unsigned int cmd, unsigned long arg)
> > +static long watchdog_ioctl(struct file *filp, unsigned int cmd,
> > +			   unsigned long arg)
> >   {
> >   	static struct watchdog_info ident = {
> >   		.options = WDIOF_KEEPALIVEPING | WDIOF_SETTIMEOUT |
> > @@ -857,11 +857,13 @@ static int watchdog_ioctl(struct inode *
> >
> >   	switch (cmd) {
> >   	case WDIOC_GETSUPPORT:
> > +		mutex_lock(&watchdog_data_mutex);
> >   		ident.firmware_version = data->revision;
> >   		if (!nowayout)
> >   			ident.options |= WDIOF_MAGICCLOSE;
> >   		if (copy_to_user((void __user *)arg,&ident, sizeof(ident)))
> >   			ret = -EFAULT;
> > +		mutex_unlock(&watchdog_data_mutex);
> >   		break;
>
> I'm not sure why we need to hold the mutex here? My understanding is
> that watchdog_data_mutex protects watchdog_data_list and each
> watchdog's kref. And the above code doesn't touch either.
>
> What I am more worried about is why ident is declared static. This
> looks like a bug to me. Instead of abusing watchdog_data_mutex to
> workaround this, I'd rather remove the "static". I guess that the
> current code happens to work because neither data->revision nor
> nowayout can change over time, but this looks needlessly fragile.
>
> Hans, any comment?

Note I'm on the road so do not have the code at question handy, but
I agree having ident static is not needed and is what needs to be fixed
here.

Regards,

Hans
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/