Messages in this thread | | | Date | Mon, 29 Nov 2010 11:56:49 -0800 | From | Greg KH <> | Subject | Re: [PATCH/RFC] core: add a function to safely try to get device driver owner |
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On Mon, Nov 29, 2010 at 08:43:28PM +0100, Guennadi Liakhovetski wrote: > When two drivers interoperate without an explicit dependency, it is often > required to prevent one of them from being unloaded safely by dereferencing > dev->driver->owner. This patch provides a generic function to do this in a > race-free way. > > Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de> > --- > > Not run-time tested in this form, but this is just a generalisation of the > code in drivers/media/video/sh_mobile_ceu_camera.c::sh_mobile_ceu_probe(). > If the idea is accepted in principle, I will replace that specific > implementation with a call to this function, test... But I am not sure, if > I'd be able to test it for races. If such testing is required on SMP, I'd > have to write some test-case for it. Thoughts? > > drivers/base/dd.c | 63 ++++++++++++++++++++++++++++++++++++++++++++++++ > include/linux/device.h | 1 + > 2 files changed, 64 insertions(+), 0 deletions(-) > > diff --git a/drivers/base/dd.c b/drivers/base/dd.c > index da57ee9..44c6672 100644 > --- a/drivers/base/dd.c > +++ b/drivers/base/dd.c > @@ -17,10 +17,12 @@ > * This file is released under the GPLv2 > */ > > +#include <linux/completion.h> > #include <linux/device.h> > #include <linux/delay.h> > #include <linux/module.h> > #include <linux/kthread.h> > +#include <linux/notifier.h> > #include <linux/wait.h> > #include <linux/async.h> > #include <linux/pm_runtime.h> > @@ -422,3 +424,64 @@ void dev_set_drvdata(struct device *dev, void *data) > dev->p->driver_data = data; > } > EXPORT_SYMBOL(dev_set_drvdata); > + > +struct bus_wait { > + struct notifier_block notifier; > + struct completion completion; > + struct device *dev; > +}; > + > +static int bus_notify(struct notifier_block *nb, > + unsigned long action, void *data) > +{ > + struct device *dev = data; > + struct bus_wait *wait = container_of(nb, struct bus_wait, notifier); > + > + if (wait->dev != dev) > + return NOTIFY_DONE; > + > + switch (action) { > + case BUS_NOTIFY_UNBOUND_DRIVER: > + /* Protect from module unloading */ > + wait_for_completion(&wait->completion); > + return NOTIFY_OK; > + } > + return NOTIFY_DONE; > +} > + > +int device_try_get_driver(struct device *dev)
Please create some kerneldoc information for this new function so that people know how to use it and what it is for.
Also, do you want to provide a device_put_driver() function as well to decrement the owner count once the person who grabed the driver is done with it?
> +{ > + struct bus_wait wait = { > + .completion = COMPLETION_INITIALIZER_ONSTACK(wait.completion), > + .dev = dev, > + .notifier.notifier_call = bus_notify, > + }; > + struct bus_type *bus; > + int ret; > + > + if (!dev || !dev->bus) > + return 0; > + > + bus = dev->bus; > + > + if (bus_register_notifier(bus, &wait.notifier) < 0) > + return 0; > + > + /* > + * From this point the driver module will not unload, until we complete > + * the completion. In the worst case it is hanging in device release on > + * our completion. So, _now_ dereferencing the "owner" is safe. > + */ > + if (dev->driver && dev->driver->owner) > + ret = try_module_get(dev->driver->owner); > + else > + /* Either no driver, or too late, or probing failed */ > + ret = 0; > + > + /* Let notifier complete, if it has been blocked */ > + complete(&wait.completion); > + bus_unregister_notifier(bus, &wait.notifier); > + > + return ret; > +} > +EXPORT_SYMBOL(device_try_get_driver);
EXPORT_SYMBOL_GPL() please.
thanks,
greg k-h
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