locking/mutex: Use try_cmpxchg()

For simpler and better code.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Waiman Long <longman@redhat.com>
Reviewed-by: Yanfei Xu <yanfei.xu@windriver.com>
Link: https://lore.kernel.org/r/20210630154114.834438545@infradead.org

diff --git a/kernel/locking/mutex.c b/kernel/locking/mutex.c
index cb6b112..cab7163 100644 (file)
--- a/kernel/locking/mutex.c
+++ b/kernel/locking/mutex.c
@@ -100,7 +100,7 @@ static inline struct task_struct *__mutex_trylock_or_owner(struct mutex *lock)
 
        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 *__mutex_trylock_or_owner(struct mutex *lock)
                 */
                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_unlock_fast(struct mutex *lock)
 {
        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
 
@@ -216,7 +210,7 @@ static void __mutex_handoff(struct mutex *lock, struct task_struct *task)
        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);
@@ -228,11 +222,8 @@ static void __mutex_handoff(struct mutex *lock, struct task_struct *task)
                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;
        }
 }
 
@@ -1229,8 +1220,6 @@ static noinline void __sched __mutex_unlock_slowpath(struct mutex *lock, unsigne
         */
        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);
@@ -1239,16 +1228,12 @@ static noinline void __sched __mutex_unlock_slowpath(struct mutex *lock, unsigne
                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);