android_kernel_samsung_msm8976/include/linux/kref.h
Linus Torvalds 5c64e3a45d Merge branch 'queue' of git://git.kernel.org/pub/scm/linux/kernel/git/nab/target-pending
Pull target fixes from Nicholas Bellinger:
 "A handful of fixes + minor changes this time around, along with one
  important >= v3.9 regression fix for IBLOCK backends.  The highlights
  include:

   - Use FD_MAX_SECTORS in FILEIO for block_device as
     well as files (agrover)

   - Fix processing of out-of-order CmdSNs with
     iSBD driver (shlomo)

   - Close long-standing target_put_sess_cmd() vs.
     core_tmr_abort_task() race with the addition of
     kref_put_spinlock_irqsave() (joern + greg-kh)

   - Fix IBLOCK WCE=1 + DPOFUA=1 backend WRITE
     regression in >= v3.9 (nab + bootc)

  Note these four patches are CC'ed to stable.

  Also, there is still some work left to be done on the active I/O
  shutdown path in target_wait_for_sess_cmds() used by tcm_qla2xxx +
  ib_isert fabrics that is still being discussed on the list, and will
  hopefully be resolved soon."

* 'queue' of git://git.kernel.org/pub/scm/linux/kernel/git/nab/target-pending:
  target: close target_put_sess_cmd() vs. core_tmr_abort_task() race
  target: removed unused transport_state flag
  target/iblock: Fix WCE=1 + DPOFUA=1 backend WRITE regression
  MAINTAINERS: Update target git tree URL
  iscsi-target: Fix typos in RDMAEXTENSIONS macro usage
  target/rd: Add ramdisk bit for NULLIO operation
  iscsi-target: Fix processing of OOO commands
  iscsi-target: Make buf param of iscsit_do_crypto_hash_buf() const void *
  iscsi-target: Fix NULL pointer dereference in iscsit_send_reject
  target: Have dev/enable show if TCM device is configured
  target: Use FD_MAX_SECTORS/FD_BLOCKSIZE for blockdevs using fileio
  target: Remove unused struct members in se_dev_entry
2013-05-16 07:55:07 -07:00

171 lines
5.4 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/bug.h>
#include <linux/atomic.h>
#include <linux/kernel.h>
#include <linux/mutex.h>
#include <linux/spinlock.h>
struct kref {
atomic_t refcount;
};
/**
* kref_init - initialize object.
* @kref: object in question.
*/
static inline void kref_init(struct kref *kref)
{
atomic_set(&kref->refcount, 1);
}
/**
* kref_get - increment refcount for object.
* @kref: object.
*/
static inline void kref_get(struct kref *kref)
{
/* If refcount was 0 before incrementing then we have a race
* condition when this kref is freeing by some other thread right now.
* In this case one should use kref_get_unless_zero()
*/
WARN_ON_ONCE(atomic_inc_return(&kref->refcount) < 2);
}
/**
* kref_sub - subtract a number of refcounts for object.
* @kref: object.
* @count: Number of recounts to subtract.
* @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.
*
* Subtract @count from 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_sub(struct kref *kref, unsigned int count,
void (*release)(struct kref *kref))
{
WARN_ON(release == NULL);
if (atomic_sub_and_test((int) count, &kref->refcount)) {
release(kref);
return 1;
}
return 0;
}
/**
* 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))
{
return kref_sub(kref, 1, release);
}
/**
* kref_put_spinlock_irqsave - 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.
* @lock: lock to take in release case
*
* Behaves identical to kref_put with one exception. If the reference count
* drops to zero, the lock will be taken atomically wrt dropping the reference
* count. The release function has to call spin_unlock() without _irqrestore.
*/
static inline int kref_put_spinlock_irqsave(struct kref *kref,
void (*release)(struct kref *kref),
spinlock_t *lock)
{
unsigned long flags;
WARN_ON(release == NULL);
if (atomic_add_unless(&kref->refcount, -1, 1))
return 0;
spin_lock_irqsave(lock, flags);
if (atomic_dec_and_test(&kref->refcount)) {
release(kref);
local_irq_restore(flags);
return 1;
}
spin_unlock_irqrestore(lock, flags);
return 0;
}
static inline int kref_put_mutex(struct kref *kref,
void (*release)(struct kref *kref),
struct mutex *lock)
{
WARN_ON(release == NULL);
if (unlikely(!atomic_add_unless(&kref->refcount, -1, 1))) {
mutex_lock(lock);
if (unlikely(!atomic_dec_and_test(&kref->refcount))) {
mutex_unlock(lock);
return 0;
}
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 atomic_add_unless(&kref->refcount, 1, 0);
}
#endif /* _KREF_H_ */