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Subject[RFC][PATCH 1/4] locking/mutex: Use try_cmpxchg()
For simpler and better code.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
kernel/locking/mutex.c | 27 ++++++---------------------
1 file changed, 6 insertions(+), 21 deletions(-)

--- a/kernel/locking/mutex.c
+++ b/kernel/locking/mutex.c
@@ -100,7 +100,7 @@ static inline struct task_struct *__mute

owner = atomic_long_read(&lock->owner);
for (;;) { /* must loop, can race against a flag */
- unsigned long old, flags = __owner_flags(owner);
+ unsigned long flags = __owner_flags(owner);
unsigned long task = owner & ~MUTEX_FLAGS;

if (task) {
@@ -124,11 +124,8 @@ static inline struct task_struct *__mute
*/
flags &= ~MUTEX_FLAG_HANDOFF;

- old = atomic_long_cmpxchg_acquire(&lock->owner, owner, curr | flags);
- if (old == owner)
+ if (atomic_long_try_cmpxchg_acquire(&lock->owner, &owner, curr | flags))
return NULL;
-
- owner = old;
}

return __owner_task(owner);
@@ -168,10 +165,7 @@ static __always_inline bool __mutex_unlo
{
unsigned long curr = (unsigned long)current;

- if (atomic_long_cmpxchg_release(&lock->owner, curr, 0UL) == curr)
- return true;
-
- return false;
+ return atomic_long_try_cmpxchg_release(&lock->owner, &curr, 0UL);
}
#endif

@@ -226,7 +220,7 @@ static void __mutex_handoff(struct mutex
unsigned long owner = atomic_long_read(&lock->owner);

for (;;) {
- unsigned long old, new;
+ unsigned long new;

#ifdef CONFIG_DEBUG_MUTEXES
DEBUG_LOCKS_WARN_ON(__owner_task(owner) != current);
@@ -238,11 +232,8 @@ static void __mutex_handoff(struct mutex
if (task)
new |= MUTEX_FLAG_PICKUP;

- old = atomic_long_cmpxchg_release(&lock->owner, owner, new);
- if (old == owner)
+ if (atomic_long_try_cmpxchg_release(&lock->owner, &owner, new))
break;
-
- owner = old;
}
}

@@ -1237,8 +1228,6 @@ static noinline void __sched __mutex_unl
*/
owner = atomic_long_read(&lock->owner);
for (;;) {
- unsigned long old;
-
#ifdef CONFIG_DEBUG_MUTEXES
DEBUG_LOCKS_WARN_ON(__owner_task(owner) != current);
DEBUG_LOCKS_WARN_ON(owner & MUTEX_FLAG_PICKUP);
@@ -1247,16 +1236,12 @@ static noinline void __sched __mutex_unl
if (owner & MUTEX_FLAG_HANDOFF)
break;

- old = atomic_long_cmpxchg_release(&lock->owner, owner,
- __owner_flags(owner));
- if (old == owner) {
+ if (atomic_long_try_cmpxchg_release(&lock->owner, &owner, __owner_flags(owner))) {
if (owner & MUTEX_FLAG_WAITERS)
break;

return;
}
-
- owner = old;
}

spin_lock(&lock->wait_lock);

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