[PATCH stable 5.10 2/7] locking/rwsem: Introduce rwsem_write_trylock()

[Shaoying Xu <shaoyi@xxxxxxxxxx>]

From: Peter Zijlstra <peterz@xxxxxxxxxxxxx>

commit 285c61aedf6bc5d81b37e4dc48c19012e8ff9836 upstream

One copy of this logic is better than three.

Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Link: https://lkml.kernel.org/r/20201207090243.GE3040@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
Cc: <stable@xxxxxxxxxxxxxxx> # 5.10
Signed-off-by: Shaoying Xu <shaoyi@xxxxxxxxxx>
---
 kernel/locking/rwsem.c | 38 ++++++++++++++++----------------------
 1 file changed, 16 insertions(+), 22 deletions(-)

diff --git a/kernel/locking/rwsem.c b/kernel/locking/rwsem.c
index 7bf45b0a1b1d..6b62654eb0a8 100644
--- a/kernel/locking/rwsem.c
+++ b/kernel/locking/rwsem.c
@@ -285,6 +285,18 @@ static inline bool rwsem_read_trylock(struct rw_semaphore *sem)
 	return false;
 }
 
+static inline bool rwsem_write_trylock(struct rw_semaphore *sem)
+{
+	long tmp = RWSEM_UNLOCKED_VALUE;
+
+	if (atomic_long_try_cmpxchg_acquire(&sem->count, &tmp, RWSEM_WRITER_LOCKED)) {
+		rwsem_set_owner(sem);
+		return true;
+	}
+
+	return false;
+}
+
 /*
  * Return just the real task structure pointer of the owner
  */
@@ -1395,42 +1407,24 @@ static inline int __down_read_trylock(struct rw_semaphore *sem)
  */
 static inline void __down_write(struct rw_semaphore *sem)
 {
-	long tmp = RWSEM_UNLOCKED_VALUE;
-
-	if (unlikely(!atomic_long_try_cmpxchg_acquire(&sem->count, &tmp,
-						      RWSEM_WRITER_LOCKED)))
+	if (unlikely(!rwsem_write_trylock(sem)))
 		rwsem_down_write_slowpath(sem, TASK_UNINTERRUPTIBLE);
-	else
-		rwsem_set_owner(sem);
 }
 
 static inline int __down_write_killable(struct rw_semaphore *sem)
 {
-	long tmp = RWSEM_UNLOCKED_VALUE;
-
-	if (unlikely(!atomic_long_try_cmpxchg_acquire(&sem->count, &tmp,
-						      RWSEM_WRITER_LOCKED))) {
+	if (unlikely(!rwsem_write_trylock(sem))) {
 		if (IS_ERR(rwsem_down_write_slowpath(sem, TASK_KILLABLE)))
 			return -EINTR;
-	} else {
-		rwsem_set_owner(sem);
 	}
+
 	return 0;
 }
 
 static inline int __down_write_trylock(struct rw_semaphore *sem)
 {
-	long tmp;
-
 	DEBUG_RWSEMS_WARN_ON(sem->magic != sem, sem);
-
-	tmp  = RWSEM_UNLOCKED_VALUE;
-	if (atomic_long_try_cmpxchg_acquire(&sem->count, &tmp,
-					    RWSEM_WRITER_LOCKED)) {
-		rwsem_set_owner(sem);
-		return true;
-	}
-	return false;
+	return rwsem_write_trylock(sem);
 }
 
 /*
-- 
2.38.1