!1203 Revert "locking/rwsem: Prevent potential lock starvation"

Merge Pull Request from: @ci-robot 
 
PR sync from: Zheng Zengkai <zhengzengkai@huawei.com>
https://mailweb.openeuler.org/hyperkitty/list/kernel@openeuler.org/message/RDUNFZSP4CQYRI7TDPSAJZDZEHHQL3H3/ 
2f06f702 ("locking/rwsem: Prevent potential lock starvation"):
This patch may have some impact on reader performance as it reduces
reader optimistic spinning especially if the lock critical sections
are short the number of contending readers are small.

This patch will lead to 30%+ performance degradation to fio write_iops_blocksize
4KB testcase, and we stress the system with mysql tpcc for 12 hours,
no hungtask occur, So revert this patchset temporarily. 
 
Link:https://gitee.com/openeuler/kernel/pulls/1203 

Reviewed-by: Xie XiuQi <xiexiuqi@huawei.com> 
Signed-off-by: Jialin Zhang <zhangjialin11@huawei.com> 

kernel/locking/rwsem.c

@@ -270,19 +270,12 @@ static inline void rwsem_set_nonspinnable(struct rw_semaphore *sem)
 					  owner | RWSEM_NONSPINNABLE));
 }
 
-static inline bool rwsem_read_trylock(struct rw_semaphore *sem, long *cntp)
+static inline bool rwsem_read_trylock(struct rw_semaphore *sem)
 {
-	*cntp = atomic_long_add_return_acquire(RWSEM_READER_BIAS, &sem->count);
-
-	if (WARN_ON_ONCE(*cntp < 0))
+	long cnt = atomic_long_add_return_acquire(RWSEM_READER_BIAS, &sem->count);
+	if (WARN_ON_ONCE(cnt < 0))
 		rwsem_set_nonspinnable(sem);
-
-	if (!(*cntp & RWSEM_READ_FAILED_MASK)) {
-		rwsem_set_reader_owned(sem);
-		return true;
-	}
-
-	return false;
+	return !(cnt & RWSEM_READ_FAILED_MASK);
 }
 
 /*
@@ -996,29 +989,18 @@ rwsem_spin_on_owner(struct rw_semaphore *sem, unsigned long nonspinnable)
  * Wait for the read lock to be granted
  */
 static struct rw_semaphore __sched *
-rwsem_down_read_slowpath(struct rw_semaphore *sem, long count, int state)
+rwsem_down_read_slowpath(struct rw_semaphore *sem, int state)
 {
-	long owner, adjustment = -RWSEM_READER_BIAS;
-	long rcnt = (count >> RWSEM_READER_SHIFT);
+	long count, adjustment = -RWSEM_READER_BIAS;
 	struct rwsem_waiter waiter;
 	DEFINE_WAKE_Q(wake_q);
 	bool wake = false;
 
-	/*
-	 * To prevent a constant stream of readers from starving a sleeping
-	 * waiter, don't attempt optimistic spinning if the lock is currently
-	 * owned by readers.
-	 */
-	owner = atomic_long_read(&sem->owner);
-	if ((owner & RWSEM_READER_OWNED) && (rcnt > 1) &&
-	   !(count & RWSEM_WRITER_LOCKED))
-		goto queue;
-
 	/*
 	 * Save the current read-owner of rwsem, if available, and the
 	 * reader nonspinnable bit.
 	 */
-	waiter.last_rowner = owner;
+	waiter.last_rowner = atomic_long_read(&sem->owner);
 	if (!(waiter.last_rowner & RWSEM_READER_OWNED))
 		waiter.last_rowner &= RWSEM_RD_NONSPINNABLE;
 
@@ -1355,34 +1337,34 @@ static struct rw_semaphore *rwsem_downgrade_wake(struct rw_semaphore *sem)
  */
 static inline void __down_read(struct rw_semaphore *sem)
 {
-	long count;
-
-	if (!rwsem_read_trylock(sem, &count)) {
-		rwsem_down_read_slowpath(sem, count, TASK_UNINTERRUPTIBLE);
+	if (!rwsem_read_trylock(sem)) {
+		rwsem_down_read_slowpath(sem, TASK_UNINTERRUPTIBLE);
 		DEBUG_RWSEMS_WARN_ON(!is_rwsem_reader_owned(sem), sem);
+	} else {
+		rwsem_set_reader_owned(sem);
 	}
 }
 
 static inline int __down_read_interruptible(struct rw_semaphore *sem)
 {
-	long count;
-
-	if (!rwsem_read_trylock(sem, &count)) {
-		if (IS_ERR(rwsem_down_read_slowpath(sem, count, TASK_INTERRUPTIBLE)))
+	if (!rwsem_read_trylock(sem)) {
+		if (IS_ERR(rwsem_down_read_slowpath(sem, TASK_INTERRUPTIBLE)))
 			return -EINTR;
 		DEBUG_RWSEMS_WARN_ON(!is_rwsem_reader_owned(sem), sem);
+	} else {
+		rwsem_set_reader_owned(sem);
 	}
 	return 0;
 }
 
 static inline int __down_read_killable(struct rw_semaphore *sem)
 {
-	long count;
-
-	if (!rwsem_read_trylock(sem, &count)) {
-		if (IS_ERR(rwsem_down_read_slowpath(sem, count, TASK_KILLABLE)))
+	if (!rwsem_read_trylock(sem)) {
+		if (IS_ERR(rwsem_down_read_slowpath(sem, TASK_KILLABLE)))
 			return -EINTR;
 		DEBUG_RWSEMS_WARN_ON(!is_rwsem_reader_owned(sem), sem);
+	} else {
+		rwsem_set_reader_owned(sem);
 	}
 	return 0;
 }