Commit f274f1e7 authored Jun 30, 2017 by Oleg Nesterov Committed by Paul E. McKenney Jul 25, 2017

task_work: Replace spin_unlock_wait() with lock/unlock pair

There is no agreed-upon definition of spin_unlock_wait()'s semantics,
and it appears that all callers could do just as well with a lock/unlock
pair. This commit therefore replaces the spin_unlock_wait() call in
task_work_run() with a spin_lock_irq() and a spin_unlock_irq() aruond
the cmpxchg() dequeue loop. This should be safe from a performance
perspective because ->pi_lock is local to the task and because calls to
the other side of the race, task_work_cancel(), should be rare.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

parent 3ef0c7a7

kernel/task_work.c

+2 −6

Original line number	Diff line number	Diff line
		@@ -96,20 +96,16 @@ void task_work_run(void)
		* work->func() can do task_work_add(), do not set
		* work_exited unless the list is empty.
		*/
		raw_spin_lock_irq(&task->pi_lock);
		do {
		work = READ_ONCE(task->task_works);
		head = !work && (task->flags & PF_EXITING) ?
		&work_exited : NULL;
		} while (cmpxchg(&task->task_works, work, head) != work);
		raw_spin_unlock_irq(&task->pi_lock);

		if (!work)
		break;
		/*
		* Synchronize with task_work_cancel(). It can't remove
		* the first entry == work, cmpxchg(task_works) should
		* fail, but it can play with *work and other entries.
		*/
		raw_spin_unlock_wait(&task->pi_lock);

		do {
		next = work->next;