rwsem: shorter spinlocked section in rwsem_down_failed_common() (f7dd1cee) · Commits · e / devices / android_kernel_xiaomi_markw

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>

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;