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Commit 1e78277c authored by Michel Lespinasse's avatar Michel Lespinasse Committed by Linus Torvalds
Browse files

rwsem: move rwsem_down_failed_common code into rwsem_down_{read,write}_failed 



Remove the rwsem_down_failed_common function and replace it with two
identical copies of its code in rwsem_down_{read,write}_failed.

This is because we want to make different optimizations in
rwsem_down_{read,write}_failed; we are adding this pure-duplication
step as a separate commit in order to make it easier to check the
following steps.

Signed-off-by: default avatarMichel Lespinasse <walken@google.com>
Reviewed-by: default avatarRik van Riel <riel@redhat.com>
Reviewed-by: default avatarPeter Hurley <peter@hurleysoftware.com>
Acked-by: default avatarDavidlohr Bueso <davidlohr.bueso@hp.com>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent f7dd1cee

lib/rwsem.c

+57 −15
Original line number Diff line number Diff line
@@ -178,12 +178,12 @@ try_again_write: 
}



/*

 * wait for a lock to be granted

 * wait for the read lock to be granted

 */

static struct rw_semaphore __sched *

rwsem_down_failed_common(struct rw_semaphore *sem,

			 enum rwsem_waiter_type type, signed long adjustment)

struct rw_semaphore __sched *rwsem_down_read_failed(struct rw_semaphore *sem)

{

	enum rwsem_waiter_type type = RWSEM_WAITING_FOR_READ;

	signed long adjustment = -RWSEM_ACTIVE_READ_BIAS;

	struct rwsem_waiter waiter;

	struct task_struct *tsk = current;

	signed long count;
@@ -237,22 +237,64 @@ rwsem_down_failed_common(struct rw_semaphore *sem, 
	return sem;

}



/*

 * wait for the read lock to be granted

 */

struct rw_semaphore __sched *rwsem_down_read_failed(struct rw_semaphore *sem)

{

	return rwsem_down_failed_common(sem, RWSEM_WAITING_FOR_READ,

					-RWSEM_ACTIVE_READ_BIAS);

}



/*

 * wait for the write lock to be granted

 */

struct rw_semaphore __sched *rwsem_down_write_failed(struct rw_semaphore *sem)

{

	return rwsem_down_failed_common(sem, RWSEM_WAITING_FOR_WRITE,

					-RWSEM_ACTIVE_WRITE_BIAS);

	enum rwsem_waiter_type type = RWSEM_WAITING_FOR_WRITE;

	signed long adjustment = -RWSEM_ACTIVE_WRITE_BIAS;

	struct rwsem_waiter waiter;

	struct task_struct *tsk = current;

	signed long count;



	/* set up my own style of waitqueue */

	waiter.task = tsk;

	waiter.type = type;

	get_task_struct(tsk);



	raw_spin_lock_irq(&sem->wait_lock);

	if (list_empty(&sem->wait_list))

		adjustment += RWSEM_WAITING_BIAS;

	list_add_tail(&waiter.list, &sem->wait_list);



	/* we're now waiting on the lock, but no longer actively locking */

	count = rwsem_atomic_update(adjustment, sem);



	/* If there are no active locks, wake the front queued process(es) up.

	 *

	 * Alternatively, if we're called from a failed down_write(), there

	 * were already threads queued before us and there are no active

	 * writers, the lock must be read owned; so we try to wake any read

	 * locks that were queued ahead of us. */

	if (count == RWSEM_WAITING_BIAS)

		sem = __rwsem_do_wake(sem, RWSEM_WAKE_NO_ACTIVE);

	else if (count > RWSEM_WAITING_BIAS &&

		 adjustment == -RWSEM_ACTIVE_WRITE_BIAS)

		sem = __rwsem_do_wake(sem, RWSEM_WAKE_READ_OWNED);



	raw_spin_unlock_irq(&sem->wait_lock);



	/* wait to be given the lock */

	while (true) {

		set_task_state(tsk, TASK_UNINTERRUPTIBLE);

		if (!waiter.task)

			break;



		raw_spin_lock_irq(&sem->wait_lock);

		/* Try to get the writer sem, may steal from the head writer: */

		if (type == RWSEM_WAITING_FOR_WRITE)

			if (try_get_writer_sem(sem, &waiter)) {

				raw_spin_unlock_irq(&sem->wait_lock);

				return sem;

			}

		raw_spin_unlock_irq(&sem->wait_lock);

		schedule();

	}



	tsk->state = TASK_RUNNING;



	return sem;

}



/*