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Subject[PATCH 4/4] scheduler: kill paranoia check in synchronize_sched_expedited()
Date
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>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Peter Zijlstra <peterz@infradead.org>
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>
---
kernel/sched.c | 40 +++-------------------------------------
1 files changed, 3 insertions(+), 37 deletions(-)
diff --git a/kernel/sched.c b/kernel/sched.c
index 947b2bb..5b88521 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -8884,14 +8884,6 @@ 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;
}

@@ -8907,55 +8899,29 @@ 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);

--
1.6.4.2


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