Unverified Commit 01c71a7b authored by openeuler-ci-bot's avatar openeuler-ci-bot Committed by Gitee
Browse files

!947 locking/rwsem: Prevent potential lock starvation 

Merge Pull Request from: @ci-robot 
 
PR sync from:  Yang Yingliang <yangyingliang@huawei.com>
 https://mailweb.openeuler.org/hyperkitty/list/kernel@openeuler.org/thread/YNL7N26QMD5Q6UDTPNELYGIOXBXP4EWZ/ 
Prevent potential lock starvation by read lock.

Peter Zijlstra (1):
  locking/rwsem: Better collate rwsem_read_trylock()

Waiman Long (2):
  locking/rwsem: Pass the current atomic count to
    rwsem_down_read_slowpath()
  locking/rwsem: Prevent potential lock starvation


-- 
2.25.1
 
 
Link:https://gitee.com/openeuler/kernel/pulls/947

 

Reviewed-by: default avatarXie XiuQi <xiexiuqi@huawei.com>
Reviewed-by: default avatarJialin Zhang <zhangjialin11@huawei.com>
Signed-off-by: default avatarJialin Zhang <zhangjialin11@huawei.com>
parents 83d60a73 924a131c

kernel/locking/rwsem.c

+37 −19
Original line number Diff line number Diff line
@@ -270,12 +270,19 @@ static inline void rwsem_set_nonspinnable(struct rw_semaphore *sem) 
					  owner | RWSEM_NONSPINNABLE));

}



static inline bool rwsem_read_trylock(struct rw_semaphore *sem)

static inline bool rwsem_read_trylock(struct rw_semaphore *sem, long *cntp)

{

	long cnt = atomic_long_add_return_acquire(RWSEM_READER_BIAS, &sem->count);

	if (WARN_ON_ONCE(cnt < 0))

	*cntp = atomic_long_add_return_acquire(RWSEM_READER_BIAS, &sem->count);



	if (WARN_ON_ONCE(*cntp < 0))

		rwsem_set_nonspinnable(sem);

	return !(cnt & RWSEM_READ_FAILED_MASK);



	if (!(*cntp & RWSEM_READ_FAILED_MASK)) {

		rwsem_set_reader_owned(sem);

		return true;

	}



	return false;

}



/*
@@ -989,18 +996,29 @@ 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, int state)

rwsem_down_read_slowpath(struct rw_semaphore *sem, long count, int state)

{

	long count, adjustment = -RWSEM_READER_BIAS;

	long owner, adjustment = -RWSEM_READER_BIAS;

	long rcnt = (count >> RWSEM_READER_SHIFT);

	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 = atomic_long_read(&sem->owner);

	waiter.last_rowner = owner;

	if (!(waiter.last_rowner & RWSEM_READER_OWNED))

		waiter.last_rowner &= RWSEM_RD_NONSPINNABLE;
@@ -1337,34 +1355,34 @@ static struct rw_semaphore *rwsem_downgrade_wake(struct rw_semaphore *sem) 
 */

static inline void __down_read(struct rw_semaphore *sem)

{

	if (!rwsem_read_trylock(sem)) {

		rwsem_down_read_slowpath(sem, TASK_UNINTERRUPTIBLE);

	long count;



	if (!rwsem_read_trylock(sem, &count)) {

		rwsem_down_read_slowpath(sem, count, 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)

{

	if (!rwsem_read_trylock(sem)) {

		if (IS_ERR(rwsem_down_read_slowpath(sem, TASK_INTERRUPTIBLE)))

	long count;



	if (!rwsem_read_trylock(sem, &count)) {

		if (IS_ERR(rwsem_down_read_slowpath(sem, count, 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)

{

	if (!rwsem_read_trylock(sem)) {

		if (IS_ERR(rwsem_down_read_slowpath(sem, TASK_KILLABLE)))

	long count;



	if (!rwsem_read_trylock(sem, &count)) {

		if (IS_ERR(rwsem_down_read_slowpath(sem, count, TASK_KILLABLE)))

			return -EINTR;

		DEBUG_RWSEMS_WARN_ON(!is_rwsem_reader_owned(sem), sem);

	} else {

		rwsem_set_reader_owned(sem);

	}

	return 0;

}