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: 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>

diff --git a/kernel/sched.c b/kernel/sched.c
index f1d577a..e9c6d79 100644 (file)
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -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);