Messages in this thread Patch in this message | | | Date | Mon, 29 Nov 2010 20:43:28 +0100 (CET) | From | Guennadi Liakhovetski <> | Subject | [PATCH/RFC] core: add a function to safely try to get device driver owner |
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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) +{ + 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); diff --git a/include/linux/device.h b/include/linux/device.h index dd48953..5932169 100644 --- a/include/linux/device.h +++ b/include/linux/device.h @@ -559,6 +559,7 @@ extern const char *device_get_devnode(struct device *dev, mode_t *mode, const char **tmp); extern void *dev_get_drvdata(const struct device *dev); extern void dev_set_drvdata(struct device *dev, void *data); +int device_try_get_driver(struct device *dev); /* * Root device objects for grouping under /sys/devices -- 1.7.2.3
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