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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: Michel Lespinasse <walken@google.com>
Reviewed-by: Rik van Riel <riel@redhat.com>
Reviewed-by: Peter Hurley <peter@hurleysoftware.com>
Acked-by: Davidlohr Bueso <davidlohr.bueso@hp.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Michel Lespinasse 2013-05-07 06:45:50 -07:00 committed by Linus Torvalds
parent e2d57f782c
commit f7dd1cee9a
1 changed files with 3 additions and 5 deletions
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8
lib/rwsem.c
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@ -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;