Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752447Ab0K2Tne (ORCPT ); Mon, 29 Nov 2010 14:43:34 -0500 Received: from moutng.kundenserver.de ([212.227.126.171]:59001 "EHLO moutng.kundenserver.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751493Ab0K2Tnd (ORCPT ); Mon, 29 Nov 2010 14:43:33 -0500 Date: Mon, 29 Nov 2010 20:43:28 +0100 (CET) From: Guennadi Liakhovetski X-X-Sender: lyakh@axis700.grange To: linux-kernel@vger.kernel.org cc: Greg KH Subject: [PATCH/RFC] core: add a function to safely try to get device driver owner Message-ID: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII X-Provags-ID: V02:K0:3/ddqxrsGJ+YzIWl8M4smJd8Xt8cQ3oLPEVy6cs4uea q5npWwcNPW1jMmYoQuYEjrhZAeGpvOKVBnXweu8cVQxYmbcNIt tPESc75OMQLlc06vU4S9lUPNi31kUFPWwl48PBiX3SXJEHsvAi LUpG1XosK6WnvyDW8iubzemQo3p2M4oE7eoP3tToWD9txZdeyM R8Cq9jrP9mYjOteP1+tQ6TjytSPl0f57giTQZMVP3g= Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3738 Lines: 121 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 --- 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 #include #include #include #include +#include #include #include #include @@ -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 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/