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Commit 94458d5e authored by Tejun Heo's avatar Tejun Heo
Browse files

sched: kill paranoia check in synchronize_sched_expedited() 



The paranoid check which verifies that the cpu_stop callback is
actually called on all online cpus is completely superflous.  It's
guaranteed by cpu_stop facility and if it didn't work as advertised
other things would go horribly wrong and trying to recover using
synchronize_sched() wouldn't be very meaningful.

Kill the paranoid check.  Removal of this feature is done as a
separate step so that it can serve as a bisection point if something
actually goes wrong.

Signed-off-by: default avatarTejun Heo <tj@kernel.org>
Acked-by: default avatarPeter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Dipankar Sarma <dipankar@in.ibm.com>
Cc: Josh Triplett <josh@freedesktop.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Dimitri Sivanich <sivanich@sgi.com>
parent 969c7921

kernel/sched.c

+3 −37
Original line number Diff line number Diff line
@@ -8953,14 +8953,6 @@ static atomic_t synchronize_sched_expedited_count = ATOMIC_INIT(0); 


static int synchronize_sched_expedited_cpu_stop(void *data)

{

	static DEFINE_SPINLOCK(done_mask_lock);

	struct cpumask *done_mask = data;



	if (done_mask) {

		spin_lock(&done_mask_lock);

		cpumask_set_cpu(smp_processor_id(), done_mask);

		spin_unlock(&done_mask_lock);

	}

	return 0;

}
@@ -8976,55 +8968,29 @@ static int synchronize_sched_expedited_cpu_stop(void *data) 
 */

void synchronize_sched_expedited(void)

{

	cpumask_var_t done_mask_var;

	struct cpumask *done_mask = NULL;

	int snap, trycount = 0;



	/*

	 * done_mask is used to check that all cpus actually have

	 * finished running the stopper, which is guaranteed by

	 * stop_cpus() if it's called with cpu hotplug blocked.  Keep

	 * the paranoia for now but it's best effort if cpumask is off

	 * stack.

	 */

	if (zalloc_cpumask_var(&done_mask_var, GFP_ATOMIC))

		done_mask = done_mask_var;



	smp_mb();  /* ensure prior mod happens before capturing snap. */

	snap = atomic_read(&synchronize_sched_expedited_count) + 1;

	get_online_cpus();

	while (try_stop_cpus(cpu_online_mask,

			     synchronize_sched_expedited_cpu_stop,

			     done_mask) == -EAGAIN) {

			     NULL) == -EAGAIN) {

		put_online_cpus();

		if (trycount++ < 10)

			udelay(trycount * num_online_cpus());

		else {

			synchronize_sched();

			goto free_out;

			return;

		}

		if (atomic_read(&synchronize_sched_expedited_count) - snap > 0) {

			smp_mb(); /* ensure test happens before caller kfree */

			goto free_out;

			return;

		}

		get_online_cpus();

	}

	atomic_inc(&synchronize_sched_expedited_count);

	if (done_mask)

		cpumask_xor(done_mask, done_mask, cpu_online_mask);

	put_online_cpus();



	/* paranoia - this can't happen */

	if (done_mask && cpumask_weight(done_mask)) {

		char buf[80];



		cpulist_scnprintf(buf, sizeof(buf), done_mask);

		WARN_ONCE(1, "synchronize_sched_expedited: cpu online and done masks disagree on %d cpus: %s\n",

			  cpumask_weight(done_mask), buf);

		synchronize_sched();

	}

free_out:

	free_cpumask_var(done_mask_var);

}

EXPORT_SYMBOL_GPL(synchronize_sched_expedited);