![Will Deacon](/assets/img/avatar_default.png)
The cmpxchg() function tends not to support 64-bit arguments on 32-bit architectures. This could be either due to use of unsigned long arguments (like on ARM) or lack of instruction support (cmpxchgq on x86). However, these architectures may implement a specific cmpxchg64() function to provide 64-bit cmpxchg support instead. Since the lockref code requires a 64-bit cmpxchg and relies on the architecture selecting ARCH_USE_CMPXCHG_LOCKREF, move to using cmpxchg64 instead of cmpxchg and allow 32-bit architectures to make use of the lockless lockref implementation. Cc: Waiman Long <Waiman.Long@hp.com> Signed-off-by: Will Deacon <will.deacon@arm.com> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
167 lines
3.4 KiB
C
167 lines
3.4 KiB
C
#include <linux/export.h>
|
|
#include <linux/lockref.h>
|
|
|
|
#ifdef CONFIG_CMPXCHG_LOCKREF
|
|
|
|
/*
|
|
* Note that the "cmpxchg()" reloads the "old" value for the
|
|
* failure case.
|
|
*/
|
|
#define CMPXCHG_LOOP(CODE, SUCCESS) do { \
|
|
struct lockref old; \
|
|
BUILD_BUG_ON(sizeof(old) != 8); \
|
|
old.lock_count = ACCESS_ONCE(lockref->lock_count); \
|
|
while (likely(arch_spin_value_unlocked(old.lock.rlock.raw_lock))) { \
|
|
struct lockref new = old, prev = old; \
|
|
CODE \
|
|
old.lock_count = cmpxchg64(&lockref->lock_count, \
|
|
old.lock_count, new.lock_count); \
|
|
if (likely(old.lock_count == prev.lock_count)) { \
|
|
SUCCESS; \
|
|
} \
|
|
cpu_relax(); \
|
|
} \
|
|
} while (0)
|
|
|
|
#else
|
|
|
|
#define CMPXCHG_LOOP(CODE, SUCCESS) do { } while (0)
|
|
|
|
#endif
|
|
|
|
/**
|
|
* lockref_get - Increments reference count unconditionally
|
|
* @lockref: pointer to lockref structure
|
|
*
|
|
* This operation is only valid if you already hold a reference
|
|
* to the object, so you know the count cannot be zero.
|
|
*/
|
|
void lockref_get(struct lockref *lockref)
|
|
{
|
|
CMPXCHG_LOOP(
|
|
new.count++;
|
|
,
|
|
return;
|
|
);
|
|
|
|
spin_lock(&lockref->lock);
|
|
lockref->count++;
|
|
spin_unlock(&lockref->lock);
|
|
}
|
|
EXPORT_SYMBOL(lockref_get);
|
|
|
|
/**
|
|
* lockref_get_not_zero - Increments count unless the count is 0
|
|
* @lockref: pointer to lockref structure
|
|
* Return: 1 if count updated successfully or 0 if count was zero
|
|
*/
|
|
int lockref_get_not_zero(struct lockref *lockref)
|
|
{
|
|
int retval;
|
|
|
|
CMPXCHG_LOOP(
|
|
new.count++;
|
|
if (!old.count)
|
|
return 0;
|
|
,
|
|
return 1;
|
|
);
|
|
|
|
spin_lock(&lockref->lock);
|
|
retval = 0;
|
|
if (lockref->count) {
|
|
lockref->count++;
|
|
retval = 1;
|
|
}
|
|
spin_unlock(&lockref->lock);
|
|
return retval;
|
|
}
|
|
EXPORT_SYMBOL(lockref_get_not_zero);
|
|
|
|
/**
|
|
* lockref_get_or_lock - Increments count unless the count is 0
|
|
* @lockref: pointer to lockref structure
|
|
* Return: 1 if count updated successfully or 0 if count was zero
|
|
* and we got the lock instead.
|
|
*/
|
|
int lockref_get_or_lock(struct lockref *lockref)
|
|
{
|
|
CMPXCHG_LOOP(
|
|
new.count++;
|
|
if (!old.count)
|
|
break;
|
|
,
|
|
return 1;
|
|
);
|
|
|
|
spin_lock(&lockref->lock);
|
|
if (!lockref->count)
|
|
return 0;
|
|
lockref->count++;
|
|
spin_unlock(&lockref->lock);
|
|
return 1;
|
|
}
|
|
EXPORT_SYMBOL(lockref_get_or_lock);
|
|
|
|
/**
|
|
* lockref_put_or_lock - decrements count unless count <= 1 before decrement
|
|
* @lockref: pointer to lockref structure
|
|
* Return: 1 if count updated successfully or 0 if count <= 1 and lock taken
|
|
*/
|
|
int lockref_put_or_lock(struct lockref *lockref)
|
|
{
|
|
CMPXCHG_LOOP(
|
|
new.count--;
|
|
if (old.count <= 1)
|
|
break;
|
|
,
|
|
return 1;
|
|
);
|
|
|
|
spin_lock(&lockref->lock);
|
|
if (lockref->count <= 1)
|
|
return 0;
|
|
lockref->count--;
|
|
spin_unlock(&lockref->lock);
|
|
return 1;
|
|
}
|
|
EXPORT_SYMBOL(lockref_put_or_lock);
|
|
|
|
/**
|
|
* lockref_mark_dead - mark lockref dead
|
|
* @lockref: pointer to lockref structure
|
|
*/
|
|
void lockref_mark_dead(struct lockref *lockref)
|
|
{
|
|
assert_spin_locked(&lockref->lock);
|
|
lockref->count = -128;
|
|
}
|
|
|
|
/**
|
|
* lockref_get_not_dead - Increments count unless the ref is dead
|
|
* @lockref: pointer to lockref structure
|
|
* Return: 1 if count updated successfully or 0 if lockref was dead
|
|
*/
|
|
int lockref_get_not_dead(struct lockref *lockref)
|
|
{
|
|
int retval;
|
|
|
|
CMPXCHG_LOOP(
|
|
new.count++;
|
|
if ((int)old.count < 0)
|
|
return 0;
|
|
,
|
|
return 1;
|
|
);
|
|
|
|
spin_lock(&lockref->lock);
|
|
retval = 0;
|
|
if ((int) lockref->count >= 0) {
|
|
lockref->count++;
|
|
retval = 1;
|
|
}
|
|
spin_unlock(&lockref->lock);
|
|
return retval;
|
|
}
|
|
EXPORT_SYMBOL(lockref_get_not_dead);
|