[PATCH] locking/rwsem: save unnecessary rwsem_set_owner() after slow path

[Peng Wang]

rwsem_down_write_failed() and rwsem_down_write_failed_killable() return
with sem->owner set if acquire semaphore successfully, so we can skip
rwsem_set_owner() to keep pace with reading.

Signed-off-by: Peng Wang <rock...@whu.edu.cn>
---
 kernel/locking/rwsem.h | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/kernel/locking/rwsem.h b/kernel/locking/rwsem.h
index 64877f5294e3..4fa21f737151 100644
--- a/kernel/locking/rwsem.h
+++ b/kernel/locking/rwsem.h
@@ -225,7 +225,8 @@ static inline void __down_write(struct rw_semaphore *sem)
                                             &sem->count);
        if (unlikely(tmp != RWSEM_ACTIVE_WRITE_BIAS))
                rwsem_down_write_failed(sem);
-       rwsem_set_owner(sem);
+       else
+               rwsem_set_owner(sem);
 }
 
 static inline int __down_write_killable(struct rw_semaphore *sem)
@@ -234,10 +235,12 @@ static inline int __down_write_killable(struct 
rw_semaphore *sem)
 
        tmp = atomic_long_add_return_acquire(RWSEM_ACTIVE_WRITE_BIAS,
                                             &sem->count);
-       if (unlikely(tmp != RWSEM_ACTIVE_WRITE_BIAS))
+       if (unlikely(tmp != RWSEM_ACTIVE_WRITE_BIAS)) {
                if (IS_ERR(rwsem_down_write_failed_killable(sem)))
                        return -EINTR;
-       rwsem_set_owner(sem);
+       } else {
+               rwsem_set_owner(sem);
+       }
        return 0;
 }
 
-- 
2.19.1