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locking/mutex: Use acquire/release semantics

Browse source 
As of 654672d4ba (locking/atomics: Add _{acquire|release|relaxed}()
variants of some atomic operations) and 6d79ef2d30 (locking, asm-generic:
Add _{relaxed|acquire|release}() variants for 'atomic_long_t'), weakly
ordered archs can benefit from more relaxed use of barriers when locking
and unlocking, instead of regular full barrier semantics. While currently
only arm64 supports such optimizations, updating corresponding locking
primitives serves for other archs to immediately benefit as well, once the
necessary machinery is implemented of course.

Signed-off-by: Davidlohr Bueso <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Reviewed-by: Thomas Gleixner <[email protected]>
Cc: Andrew Morton <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Paul E. McKenney <[email protected]>
Cc: Paul E.McKenney <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Will Deacon <[email protected]>
Cc: [email protected]
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>
This commit is contained in:
Davidlohr Bueso 2015-09-30 13:03:12 -07:00 • committed by Ingo Molnar
commit 81a43adae3
3 changed files with 14 additions and 13 deletions
Download patch file Download diff file Expand all files Collapse all files

8
include/asm-generic/mutex-dec.h
View file

@ -20,7 +20,7 @@
static inline void
__mutex_fastpath_lock(atomic_t *count, void (*fail_fn)(atomic_t *))
{
if (unlikely(atomic_dec_return(count) < 0))
if (unlikely(atomic_dec_return_acquire(count) < 0))
fail_fn(count);
}
@ -35,7 +35,7 @@ __mutex_fastpath_lock(atomic_t *count, void (*fail_fn)(atomic_t *))
static inline int
__mutex_fastpath_lock_retval(atomic_t *count)
{
if (unlikely(atomic_dec_return(count) < 0))
if (unlikely(atomic_dec_return_acquire(count) < 0))
return -1;
return 0;
}
@ -56,7 +56,7 @@ __mutex_fastpath_lock_retval(atomic_t *count)
static inline void
__mutex_fastpath_unlock(atomic_t *count, void (*fail_fn)(atomic_t *))
{
if (unlikely(atomic_inc_return(count) <= 0))
if (unlikely(atomic_inc_return_release(count) <= 0))
fail_fn(count);
}
@ -80,7 +80,7 @@ __mutex_fastpath_unlock(atomic_t *count, void (*fail_fn)(atomic_t *))
static inline int
__mutex_fastpath_trylock(atomic_t *count, int (*fail_fn)(atomic_t *))
{
if (likely(atomic_cmpxchg(count, 1, 0) == 1))
if (likely(atomic_cmpxchg_acquire(count, 1, 0) == 1))
return 1;
return 0;
}

10
include/asm-generic/mutex-xchg.h
View file

@ -31,7 +31,7 @@ __mutex_fastpath_lock(atomic_t *count, void (*fail_fn)(atomic_t *))
* to ensure that any waiting tasks are woken up by the
* unlock slow path.
*/
if (likely(atomic_xchg(count, -1) != 1))
if (likely(atomic_xchg_acquire(count, -1) != 1))
fail_fn(count);
}
@ -46,7 +46,7 @@ __mutex_fastpath_lock(atomic_t *count, void (*fail_fn)(atomic_t *))
static inline int
__mutex_fastpath_lock_retval(atomic_t *count)
{
if (unlikely(atomic_xchg(count, 0) != 1))
if (unlikely(atomic_xchg_acquire(count, 0) != 1))
if (likely(atomic_xchg(count, -1) != 1))
return -1;
return 0;
@ -67,7 +67,7 @@ __mutex_fastpath_lock_retval(atomic_t *count)
static inline void
__mutex_fastpath_unlock(atomic_t *count, void (*fail_fn)(atomic_t *))
{
if (unlikely(atomic_xchg(count, 1) != 0))
if (unlikely(atomic_xchg_release(count, 1) != 0))
fail_fn(count);
}
@ -91,7 +91,7 @@ __mutex_fastpath_unlock(atomic_t *count, void (*fail_fn)(atomic_t *))
static inline int
__mutex_fastpath_trylock(atomic_t *count, int (*fail_fn)(atomic_t *))
{
int prev = atomic_xchg(count, 0);
int prev = atomic_xchg_acquire(count, 0);
if (unlikely(prev < 0)) {
/*
@ -105,7 +105,7 @@ __mutex_fastpath_trylock(atomic_t *count, int (*fail_fn)(atomic_t *))
* owner's unlock path needlessly, but that's not a problem
* in practice. ]
*/
prev = atomic_xchg(count, prev);
prev = atomic_xchg_acquire(count, prev);
if (prev < 0)
prev = 0;
}