On Thu, Nov 12, 2020 at 07:52:14PM +0200, Andy Shevchenko wrote:
> On Thu, Nov 12, 2020 at 6:40 PM Nicolas Saenz Julienne
> <nsaenzjulienne@xxxxxxx> wrote:
> >
> > When unbinding the firmware device we need to make sure it has no
> > consumers left. Otherwise we'd leave them with a firmware handle
> > pointing at freed memory.
> >
> > Keep a reference count of all consumers and introduce rpi_firmware_put()
> > which will permit automatically decrease the reference count upon
> > unbinding consumer drivers.
>
> ...
>
> > /**
> > - * rpi_firmware_get - Get pointer to rpi_firmware structure.
> > * @firmware_node: Pointer to the firmware Device Tree node.
> > *
> > + * The reference to rpi_firmware has to be released with rpi_firmware_put().
> > + *
> > * Returns NULL is the firmware device is not ready.
> > */
> > struct rpi_firmware *rpi_firmware_get(struct device_node *firmware_node)
> > {
> > struct platform_device *pdev = of_find_device_by_node(firmware_node);
> > + struct rpi_firmware *fw;
> >
> > if (!pdev)
> > return NULL;
> >
> > - return platform_get_drvdata(pdev);
> > + fw = platform_get_drvdata(pdev);
> > + if (!fw)
> > + return NULL;
> > +
> > + if (!kref_get_unless_zero(&fw->consumers))
> > + return NULL;
>
> Don't we have a more traditional way of doing this, i.e.
> try_module_get() coupled with get_device() ?
get_device() will make sure that device is there, but gives no
assurances that device is bound to a driver, so it will not help with
the racy access to firmware via platform_get_drvdata() call.
Thanks.
--
Dmitry
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