linux-stable/include/linux/kref.h
Andi Kleen ec48c940da kref: remove WARN_ON for NULL release functions
The kref functions check for NULL release functions.  This WARN_ON seems
rather pointless.  We will eventually release and then just crash
nicely.  It is also somewhat expensive because these functions are
inlined in a lot of places.  Removing the WARN_ONs saves around 2.3k in
this kernel (likely more in others with more drivers)

     text    data     bss     dec     hex filename
  9083992 5367600 11116544        25568136        1862388 vmlinux-before-load-avg
  9070166 5367600 11116544        25554310        185ed86 vmlinux-load-avg

Link: http://lkml.kernel.org/r/20170315021431.13107-5-andi@firstfloor.org
Signed-off-by: Andi Kleen <ak@linux.intel.com>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2017-05-08 17:15:14 -07:00

118 lines
3.3 KiB
C

/*
* kref.h - library routines for handling generic reference counted objects
*
* Copyright (C) 2004 Greg Kroah-Hartman <greg@kroah.com>
* Copyright (C) 2004 IBM Corp.
*
* based on kobject.h which was:
* Copyright (C) 2002-2003 Patrick Mochel <mochel@osdl.org>
* Copyright (C) 2002-2003 Open Source Development Labs
*
* This file is released under the GPLv2.
*
*/
#ifndef _KREF_H_
#define _KREF_H_
#include <linux/spinlock.h>
#include <linux/refcount.h>
struct kref {
refcount_t refcount;
};
#define KREF_INIT(n) { .refcount = REFCOUNT_INIT(n), }
/**
* kref_init - initialize object.
* @kref: object in question.
*/
static inline void kref_init(struct kref *kref)
{
refcount_set(&kref->refcount, 1);
}
static inline unsigned int kref_read(const struct kref *kref)
{
return refcount_read(&kref->refcount);
}
/**
* kref_get - increment refcount for object.
* @kref: object.
*/
static inline void kref_get(struct kref *kref)
{
refcount_inc(&kref->refcount);
}
/**
* 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. 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.
*
* 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.
*/
static inline int kref_put(struct kref *kref, void (*release)(struct kref *kref))
{
if (refcount_dec_and_test(&kref->refcount)) {
release(kref);
return 1;
}
return 0;
}
static inline int kref_put_mutex(struct kref *kref,
void (*release)(struct kref *kref),
struct mutex *lock)
{
if (refcount_dec_and_mutex_lock(&kref->refcount, lock)) {
release(kref);
return 1;
}
return 0;
}
static inline int kref_put_lock(struct kref *kref,
void (*release)(struct kref *kref),
spinlock_t *lock)
{
if (refcount_dec_and_lock(&kref->refcount, lock)) {
release(kref);
return 1;
}
return 0;
}
/**
* kref_get_unless_zero - Increment refcount for object unless it is zero.
* @kref: object.
*
* Return non-zero if the increment succeeded. Otherwise return 0.
*
* This function is intended to simplify locking around refcounting for
* objects that can be looked up from a lookup structure, and which are
* removed from that lookup structure in the object destructor.
* Operations on such objects require at least a read lock around
* lookup + kref_get, and a write lock around kref_put + remove from lookup
* structure. Furthermore, RCU implementations become extremely tricky.
* With a lookup followed by a kref_get_unless_zero *with return value check*
* locking in the kref_put path can be deferred to the actual removal from
* the lookup structure and RCU lookups become trivial.
*/
static inline int __must_check kref_get_unless_zero(struct kref *kref)
{
return refcount_inc_not_zero(&kref->refcount);
}
#endif /* _KREF_H_ */