linux-stable/lib/kref.c
Oliver Neukum 1b0b3b9980 kref: fix CPU ordering with respect to krefs
some atomic operations are only atomic, not ordered. Thus a CPU is allowed
to reorder memory references to an object to before the reference is
obtained. This fixes it.

Signed-off-by: Oliver Neukum <oneukum@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
2007-04-27 10:57:29 -07:00

66 lines
1.6 KiB
C

/*
* kref.c - library routines for handling generic reference counted objects
*
* Copyright (C) 2004 Greg Kroah-Hartman <greg@kroah.com>
* Copyright (C) 2004 IBM Corp.
*
* based on lib/kobject.c which was:
* Copyright (C) 2002-2003 Patrick Mochel <mochel@osdl.org>
*
* This file is released under the GPLv2.
*
*/
#include <linux/kref.h>
#include <linux/module.h>
/**
* kref_init - initialize object.
* @kref: object in question.
*/
void kref_init(struct kref *kref)
{
atomic_set(&kref->refcount,1);
smp_mb();
}
/**
* kref_get - increment refcount for object.
* @kref: object.
*/
void kref_get(struct kref *kref)
{
WARN_ON(!atomic_read(&kref->refcount));
atomic_inc(&kref->refcount);
smp_mb__after_atomic_inc();
}
/**
* kref_put - decrement refcount for object.
* @kref: object.
* @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.
*
* Decrement the refcount, and if 0, call release().
* Return 1 if the object was removed, otherwise return 0. Beware, if this
* function returns 0, you still can not count on the kref from remaining in
* memory. Only use the return value if you want to see if the kref is now
* gone, not present.
*/
int kref_put(struct kref *kref, void (*release)(struct kref *kref))
{
WARN_ON(release == NULL);
WARN_ON(release == (void (*)(struct kref *))kfree);
if (atomic_dec_and_test(&kref->refcount)) {
release(kref);
return 1;
}
return 0;
}
EXPORT_SYMBOL(kref_init);
EXPORT_SYMBOL(kref_get);
EXPORT_SYMBOL(kref_put);