2021-07-08 08:43:46

by tip-bot2 for Haifeng Xu

Subject: [tip: locking/core] locking/mutex: Use try_cmpxchg()

The following commit has been merged into the locking/core branch of tip:

Commit-ID: ab4e4d9f79b2c95ef268985d2a9625a03a73c49a
Gitweb: https://git.kernel.org/tip/ab4e4d9f79b2c95ef268985d2a9625a03a73c49a
Author: Peter Zijlstra <[email protected]>
AuthorDate: Wed, 30 Jun 2021 17:35:17 +02:00
Committer: Peter Zijlstra <[email protected]>
CommitterDate: Wed, 07 Jul 2021 13:53:24 +02:00

locking/mutex: Use try_cmpxchg()

For simpler and better code.

Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Reviewed-by: Waiman Long <[email protected]>
Reviewed-by: Yanfei Xu <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
---
kernel/locking/mutex.c | 27 ++++++---------------------
1 file changed, 6 insertions(+), 21 deletions(-)

diff --git a/kernel/locking/mutex.c b/kernel/locking/mutex.c
index cb6b112..cab7163 100644
--- 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);