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Commit 4897dd95 authored by Michel Lespinasse's avatar Michel Lespinasse Committed by Samuel Pascua
Browse files

rwsem: shorter spinlocked section in rwsem_down_failed_common() 



This change reduces the size of the spinlocked and TASK_UNINTERRUPTIBLE
sections in rwsem_down_failed_common():

- We only need the sem->wait_lock to insert ourselves on the wait_list;
  the waiter node can be prepared outside of the wait_lock.

- The task state only needs to be set to TASK_UNINTERRUPTIBLE immediately
  before checking if we actually need to sleep; it doesn't need to protect
  the entire function.

Signed-off-by: default avatarMichel Lespinasse <walken@google.com>
parent 5b9c5a1c

lib/rwsem.c

+3 −5
Original line number Diff line number Diff line
@@ -188,14 +188,12 @@ rwsem_down_failed_common(struct rw_semaphore *sem, 
	struct task_struct *tsk = current;

	signed long count;



	set_task_state(tsk, TASK_UNINTERRUPTIBLE);



	/* set up my own style of waitqueue */

	raw_spin_lock_irq(&sem->wait_lock);

	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);
@@ -218,7 +216,8 @@ rwsem_down_failed_common(struct rw_semaphore *sem, 
	raw_spin_unlock_irq(&sem->wait_lock);



	/* wait to be given the lock */

	for (;;) {

	while (true) {

		set_task_state(tsk, TASK_UNINTERRUPTIBLE);

		if (!waiter.task)

			break;
@@ -231,7 +230,6 @@ rwsem_down_failed_common(struct rw_semaphore *sem, 
			}

		raw_spin_unlock_irq(&sem->wait_lock);

		schedule();

		set_task_state(tsk, TASK_UNINTERRUPTIBLE);

	}



	tsk->state = TASK_RUNNING;