Commit 186bddb2 authored by Ezequiel Garcia's avatar Ezequiel Garcia Committed by Greg Kroah-Hartman
Browse files

kref/kobject: Improve documentation 



The current kref and kobject documentation may be
insufficient to understand these common pitfalls regarding
object lifetime and object releasing.

Add a bit more documentation and improve the warnings
seen by the user, pointing to the right piece of documentation.

Also, it's important to understand that making fun of people
publicly is not at all helpful, doesn't provide any value,
and it's not a healthy way of encouraging developers to do better.

"Mocking mercilessly" will, if anything, make developers feel bad
and go away. This kind of behavior should not be encouraged or justified.

Signed-off-by: default avatarEzequiel Garcia <ezequiel@collabora.com>
Signed-off-by: default avatarEnric Balletbo i Serra <enric.balletbo@collabora.com>
Signed-off-by: default avatarGustavo Padovan <gustavo.padovan@collabora.com>
Signed-off-by: default avatarMatthias Brugger <mbrugger@suse.com>
Acked-by: default avatarDaniel Vetter <daniel.vetter@ffwll.ch>
Acked-by: default avatarGuenter Roeck <linux@roeck-us.net>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 3f8e9178

Documentation/kobject.txt

+7 −3
Original line number Diff line number Diff line
@@ -281,8 +281,12 @@ release() method, and the kobject must persist (in a consistent state) 
until that method is called. If these constraints are not met, the code is

flawed. Note that the kernel will warn you if you forget to provide a

release() method.  Do not try to get rid of this warning by providing an

"empty" release function; you will be mocked mercilessly by the kobject

maintainer if you attempt this.

"empty" release function.



If all your cleanup function needs to do is call kfree(), then you must

create a wrapper function which uses container_of() to upcast to the correct

type (as shown in the example above) and then calls kfree() on the overall

structure.



Note, the name of the kobject is available in the release function, but it

must NOT be changed within this callback.  Otherwise there will be a memory

drivers/base/core.c

+1 −2
Original line number Diff line number Diff line
@@ -897,8 +897,7 @@ static void device_release(struct kobject *kobj) 
	else if (dev->class && dev->class->dev_release)

		dev->class->dev_release(dev);

	else

		WARN(1, KERN_ERR "Device '%s' does not have a release() "

			"function, it is broken and must be fixed.\n",

		WARN(1, KERN_ERR "Device '%s' does not have a release() function, it is broken and must be fixed. See Documentation/kobject.txt.\n",

			dev_name(dev));

	kfree(p);

}

include/linux/kref.h

+1 −4
Original line number Diff line number Diff line
@@ -53,10 +53,7 @@ static inline void kref_get(struct kref *kref) 
 * @release: pointer to the function that will clean up the object when the

 *	     last reference to the object is released.

 *	     This pointer is required, and it is not acceptable to pass kfree

 *	     in as this function.  If the caller does pass kfree to this

 *	     function, you will be publicly mocked mercilessly by the kref

 *	     maintainer, and anyone else who happens to notice it.  You have

 *	     been warned.

 *	     in as this function.

 *

 * Decrement the refcount, and if 0, call release().

 * Return 1 if the object was removed, otherwise return 0.  Beware, if this

lib/kobject.c

+1 −1
Original line number Diff line number Diff line
@@ -639,7 +639,7 @@ static void kobject_cleanup(struct kobject *kobj) 
		 kobject_name(kobj), kobj, __func__, kobj->parent);



	if (t && !t->release)

		pr_debug("kobject: '%s' (%p): does not have a release() function, it is broken and must be fixed.\n",

		pr_debug("kobject: '%s' (%p): does not have a release() function, it is broken and must be fixed. See Documentation/kobject.txt.\n",

			 kobject_name(kobj), kobj);



	/* send "remove" if the caller did not do it but sent "add" */

CRA Git | Maintained and supported by SUSTech CRA and CCSE