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sched: kill paranoia check in synchronize_sched_expedited()

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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: Tejun Heo <tj@kernel.org>
Acked-by: Peter 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>
This commit is contained in:
Tejun Heo 2010-05-06 18:49:21 +02:00
parent 969c79215a
commit 94458d5ecb
1 changed files with 3 additions and 37 deletions
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40
kernel/sched.c
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@ -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);