Re: [PATCH 1/2] Initial support for Allwinner's Security ID fuses

[Greg KH <gregkh@linuxfoundation.org>]

On Wed, Jun 26, 2013 at 11:22:30AM +0200, Geert Uytterhoeven wrote:
> On Mon, Jun 24, 2013 at 6:04 PM, Greg KH <gregkh@linuxfoundation.org> wrote:
> > On Mon, Jun 24, 2013 at 11:29:42AM +0200, Maxime Ripard wrote:
> >> On Mon, Jun 17, 2013 at 03:58:47PM -0700, Greg KH wrote:
> >> > On Mon, Jun 17, 2013 at 10:59:37PM +0200, Oliver Schinagl wrote:
> >> > > +static int __init sunxi_sid_probe(struct platform_device *pdev)
> >> > > +{
> >> > > + u8 entropy[SID_SIZE];
> >> > > + unsigned int i;
> >> > > + struct resource *res;
> >> > > + void __iomem *sid_reg_base;
> >> > > + int ret;
> >> > > +
> >> > > + res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
> >> > > + sid_reg_base = devm_ioremap_resource(&pdev->dev, res);
> >> > > + if (IS_ERR(sid_reg_base))
> >> > > +         return PTR_ERR(sid_reg_base);
> >> > > + platform_set_drvdata(pdev, sid_reg_base);
> >> > > +
> >> > > + ret = device_create_bin_file(&pdev->dev, &sid_bin_attr);
> >> > > + if (ret)
> >> > > +         return ret;
> >> >
> >> > You just raced with userspace, having the file show up after the device
> >> > was announced to users that it was there.  Please use the proper device
> >> > file api to add default attributes to prevent this from happening.
> >>
> >> Sorry if the question looks dumb, but what kind of race can we generate
> >> here?
> >
> > Userspace gets told about the device from the driver core, udev runs and
> > reads all of the attributes, then your probe function comes along and
> > adds a new attribute.  Userspace will then not know about it at all.
> >
> >> The device_create_bin_file is the last call that we make (if we except
> >> the entropy stuff, but it doesn't really matter here), so after we
> >> created the file, we have everything properly initialised so that our
> >> functions can be called, right?
> >>
> >> And another dumb question for you, what is the "proper device file API"
> >> you are referring to ? :)
> >
> > Please read Documentation/driver_model/device.txt and see the section on
> > Attributes for what to do.  If you have specific questions after reading
> > that, please let me know.
> 
> Woops, then we have plenty of existing drivers to fix, e.g. all/most RTC drivers
> exposing an NVRAM file through sysfs:
> 
> $ git grep -w sysfs_create_bin_file drivers/rtc/
> drivers/rtc/rtc-cmos.c: retval = sysfs_create_bin_file(&dev->kobj, &nvram);
> drivers/rtc/rtc-ds1305.c: status =
> sysfs_create_bin_file(&spi->dev.kobj, &nvram);
> drivers/rtc/rtc-ds1307.c: err =
> sysfs_create_bin_file(&client->dev.kobj, ds1307->nvram);
> drivers/rtc/rtc-ds1511.c: ret = sysfs_create_bin_file(&pdev->dev.kobj,
> &ds1511_nvram_attr);
> drivers/rtc/rtc-ds1553.c: ret = sysfs_create_bin_file(&pdev->dev.kobj,
> &ds1553_nvram_attr);
> drivers/rtc/rtc-ds1742.c: ret = sysfs_create_bin_file(&pdev->dev.kobj,
> &pdata->nvram_attr);
> drivers/rtc/rtc-m48t59.c: ret = sysfs_create_bin_file(&pdev->dev.kobj,
> &m48t59_nvram_attr);
> drivers/rtc/rtc-rp5c01.c: error =
> sysfs_create_bin_file(&dev->dev.kobj, &priv->nvram_attr);
> drivers/rtc/rtc-stk17ta8.c: ret =
> sysfs_create_bin_file(&pdev->dev.kobj, &stk17ta8_nvram_attr);
> drivers/rtc/rtc-tx4939.c: ret = sysfs_create_bin_file(&pdev->dev.kobj,
> &tx4939_rtc_nvram_attr);

Yes, they should all be fixed, along with any platform device that
creates a sysfs file in the probe function.

thanks,

greg k-h