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    SubjectRe: Using statically allocated memory for platform_data.
    On Mon, Nov 02, 2009 at 11:39:40AM +0100, Uwe Kleine-K?nig wrote:
    > Hello,
    >
    > On Mon, Nov 02, 2009 at 11:23:16AM +0100, Antonio Ospite wrote:
    > > Hi,
    > >
    > > I noted that in some mfd drivers (drivers/mfd/ezx-pcap.c and
    > > drivers/mfd/da903x.c) there is code like this:
    > >
    > > static int __devinit pcap_add_subdev(struct pcap_chip *pcap,
    > > struct pcap_subdev *subdev)
    > > {
    > > struct platform_device *pdev;
    > >
    > > pdev = platform_device_alloc(subdev->name, subdev->id);
    > > pdev->dev.parent = &pcap->spi->dev;
    > > pdev->dev.platform_data = subdev->platform_data;
    > >
    > > return platform_device_add(pdev);
    > > }
    > >
    > > Note the _direct_assignment_ of platform data; then in board init code
    > > there are often global struct pointers passed as subdev platform data,
    > > see arch/arm/mach-pxa/em-x270.c::em_x270_da9030_subdevs for instance.
    > >
    > > In these cases, whenever the subdev platform device is unregistered,
    > > the call to platform_device_release() tries to kfree the platform data,
    > > and being it statically allocated memory this triggers a bug from SLAB:
    > > kernel BUG at mm/slab.c:521!
    > > In my case this prevented proper device poweroff.
    > >
    > > The question: should these mfd drivers use platform_device_add_data()
    > > which allocates dynamic memory for *a copy* of platform data? Is this
    > > simple solution acceptable even if there will be more memory used?
    > If you move the original data lives in .init there is no duplication.

    they you can't modprobe devices after loading the kernel, so udev
    autoload and the like become impossible.

    --
    Ben (ben@fluff.org, http://www.fluff.org/)

    'a smiley only costs 4 bytes'


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