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Commit bac78573 authored by Oleg Nesterov's avatar Oleg Nesterov Committed by Ingo Molnar
Browse files

sched/fair: Use task_rcu_dereference() 



Simplify task_numa_compare()'s task reference magic by using
task_rcu_dereference().

Signed-off-by: default avatarOleg Nesterov <oleg@redhat.com>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: Chris Metcalf <cmetcalf@ezchip.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Kirill Tkhai <ktkhai@parallels.com>
Cc: Kirill Tkhai <tkhai@yandex.ru>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vladimir Davydov <vdavydov@parallels.com>
Link: http://lkml.kernel.org/r/20160518195733.GA15914@redhat.com


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent 150593bf

kernel/sched/fair.c

+4 −30
Original line number Diff line number Diff line
@@ -1305,6 +1305,8 @@ static void task_numa_assign(struct task_numa_env *env, 
{

	if (env->best_task)

		put_task_struct(env->best_task);

	if (p)

		get_task_struct(p);



	env->best_task = p;

	env->best_imp = imp;
@@ -1372,31 +1374,11 @@ static void task_numa_compare(struct task_numa_env *env, 
	long imp = env->p->numa_group ? groupimp : taskimp;

	long moveimp = imp;

	int dist = env->dist;

	bool assigned = false;



	rcu_read_lock();



	raw_spin_lock_irq(&dst_rq->lock);

	cur = dst_rq->curr;

	/*

	 * No need to move the exiting task or idle task.

	 */

	if ((cur->flags & PF_EXITING) || is_idle_task(cur))

	cur = task_rcu_dereference(&dst_rq->curr);

	if (cur && ((cur->flags & PF_EXITING) || is_idle_task(cur)))

		cur = NULL;

	else {

		/*

		 * The task_struct must be protected here to protect the

		 * p->numa_faults access in the task_weight since the

		 * numa_faults could already be freed in the following path:

		 * finish_task_switch()

		 *     --> put_task_struct()

		 *         --> __put_task_struct()

		 *             --> task_numa_free()

		 */

		get_task_struct(cur);

	}



	raw_spin_unlock_irq(&dst_rq->lock);



	/*

	 * Because we have preemption enabled we can get migrated around and
@@ -1479,7 +1461,6 @@ static void task_numa_compare(struct task_numa_env *env, 
		 */

		if (!load_too_imbalanced(src_load, dst_load, env)) {

			imp = moveimp - 1;

			put_task_struct(cur);

			cur = NULL;

			goto assign;

		}
@@ -1505,16 +1486,9 @@ static void task_numa_compare(struct task_numa_env *env, 
		env->dst_cpu = select_idle_sibling(env->p, env->dst_cpu);



assign:

	assigned = true;

	task_numa_assign(env, cur, imp);

unlock:

	rcu_read_unlock();

	/*

	 * The dst_rq->curr isn't assigned. The protection for task_struct is

	 * finished.

	 */

	if (cur && !assigned)

		put_task_struct(cur);

}



static void task_numa_find_cpu(struct task_numa_env *env,