Release 4.7 include/asm-generic/mutex-xchg.h
/*
* include/asm-generic/mutex-xchg.h
*
* Generic implementation of the mutex fastpath, based on xchg().
*
* NOTE: An xchg based implementation might be less optimal than an atomic
* decrement/increment based implementation. If your architecture
* has a reasonable atomic dec/inc then you should probably use
* asm-generic/mutex-dec.h instead, or you could open-code an
* optimized version in asm/mutex.h.
*/
#ifndef _ASM_GENERIC_MUTEX_XCHG_H
#define _ASM_GENERIC_MUTEX_XCHG_H
/**
* __mutex_fastpath_lock - try to take the lock by moving the count
* from 1 to a 0 value
* @count: pointer of type atomic_t
* @fail_fn: function to call if the original value was not 1
*
* Change the count from 1 to a value lower than 1, and call <fail_fn> if it
* wasn't 1 originally. This function MUST leave the value lower than 1
* even when the "1" assertion wasn't true.
*/
static inline void
__mutex_fastpath_lock(atomic_t *count, void (*fail_fn)(atomic_t *))
{
if (unlikely(atomic_xchg(count, 0) != 1))
/*
* We failed to acquire the lock, so mark it contended
* to ensure that any waiting tasks are woken up by the
* unlock slow path.
*/
if (likely(atomic_xchg_acquire(count, -1) != 1))
fail_fn(count);
}
Contributors
| Person | Tokens | Prop | Commits | CommitProp |
| nicolas pitre | nicolas pitre | 27 | 48.21% | 1 | 20.00% |
| will deacon | will deacon | 15 | 26.79% | 1 | 20.00% |
| harvey harrison | harvey harrison | 10 | 17.86% | 1 | 20.00% |
| ingo molnar | ingo molnar | 3 | 5.36% | 1 | 20.00% |
| davidlohr bueso | davidlohr bueso | 1 | 1.79% | 1 | 20.00% |
| Total | 56 | 100.00% | 5 | 100.00% |
/**
* __mutex_fastpath_lock_retval - try to take the lock by moving the count
* from 1 to a 0 value
* @count: pointer of type atomic_t
*
* Change the count from 1 to a value lower than 1. This function returns 0
* if the fastpath succeeds, or -1 otherwise.
*/
static inline int
__mutex_fastpath_lock_retval(atomic_t *count)
{
if (unlikely(atomic_xchg_acquire(count, 0) != 1))
if (likely(atomic_xchg(count, -1) != 1))
return -1;
return 0;
}
Contributors
| Person | Tokens | Prop | Commits | CommitProp |
| ingo molnar | ingo molnar | 26 | 55.32% | 1 | 20.00% |
| will deacon | will deacon | 15 | 31.91% | 1 | 20.00% |
| harvey harrison | harvey harrison | 3 | 6.38% | 1 | 20.00% |
| maarten lankhorst | maarten lankhorst | 2 | 4.26% | 1 | 20.00% |
| davidlohr bueso | davidlohr bueso | 1 | 2.13% | 1 | 20.00% |
| Total | 47 | 100.00% | 5 | 100.00% |
/**
* __mutex_fastpath_unlock - try to promote the mutex from 0 to 1
* @count: pointer of type atomic_t
* @fail_fn: function to call if the original value was not 0
*
* try to promote the mutex from 0 to 1. if it wasn't 0, call <function>
* In the failure case, this function is allowed to either set the value to
* 1, or to set it to a value lower than one.
* If the implementation sets it to a value of lower than one, the
* __mutex_slowpath_needs_to_unlock() macro needs to return 1, it needs
* to return 0 otherwise.
*/
static inline void
__mutex_fastpath_unlock(atomic_t *count, void (*fail_fn)(atomic_t *))
{
if (unlikely(atomic_xchg_release(count, 1) != 0))
fail_fn(count);
}
Contributors
| Person | Tokens | Prop | Commits | CommitProp |
| nicolas pitre | nicolas pitre | 26 | 65.00% | 1 | 25.00% |
| harvey harrison | harvey harrison | 10 | 25.00% | 1 | 25.00% |
| ingo molnar | ingo molnar | 3 | 7.50% | 1 | 25.00% |
| davidlohr bueso | davidlohr bueso | 1 | 2.50% | 1 | 25.00% |
| Total | 40 | 100.00% | 4 | 100.00% |
#define __mutex_slowpath_needs_to_unlock() 0
/**
* __mutex_fastpath_trylock - try to acquire the mutex, without waiting
*
* @count: pointer of type atomic_t
* @fail_fn: spinlock based trylock implementation
*
* Change the count from 1 to a value lower than 1, and return 0 (failure)
* if it wasn't 1 originally, or return 1 (success) otherwise. This function
* MUST leave the value lower than 1 even when the "1" assertion wasn't true.
* Additionally, if the value was < 0 originally, this function must not leave
* it to 0 on failure.
*
* If the architecture has no effective trylock variant, it should call the
* <fail_fn> spinlock-based trylock variant unconditionally.
*/
static inline int
__mutex_fastpath_trylock(atomic_t *count, int (*fail_fn)(atomic_t *))
{
int prev = atomic_xchg_acquire(count, 0);
if (unlikely(prev < 0)) {
/*
* The lock was marked contended so we must restore that
* state. If while doing so we get back a prev value of 1
* then we just own it.
*
* [ In the rare case of the mutex going to 1, to 0, to -1
* and then back to 0 in this few-instructions window,
* this has the potential to trigger the slowpath for the
* owner's unlock path needlessly, but that's not a problem
* in practice. ]
*/
prev = atomic_xchg_acquire(count, prev);
if (prev < 0)
prev = 0;
}
return prev;
}
Contributors
| Person | Tokens | Prop | Commits | CommitProp |
| ingo molnar | ingo molnar | 63 | 96.92% | 1 | 50.00% |
| davidlohr bueso | davidlohr bueso | 2 | 3.08% | 1 | 50.00% |
| Total | 65 | 100.00% | 2 | 100.00% |
#endif
Overall Contributors
| Person | Tokens | Prop | Commits | CommitProp |
| ingo molnar | ingo molnar | 111 | 49.12% | 1 | 14.29% |
| nicolas pitre | nicolas pitre | 53 | 23.45% | 1 | 14.29% |
| will deacon | will deacon | 30 | 13.27% | 1 | 14.29% |
| harvey harrison | harvey harrison | 23 | 10.18% | 1 | 14.29% |
| davidlohr bueso | davidlohr bueso | 5 | 2.21% | 1 | 14.29% |
| maarten lankhorst | maarten lankhorst | 3 | 1.33% | 1 | 14.29% |
| uwe zeisberger | uwe zeisberger | 1 | 0.44% | 1 | 14.29% |
| Total | 226 | 100.00% | 7 | 100.00% |
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