linux-kernel - [PATCH tip/core/rcu 43/88] sched: Rely on synchronize_rcu

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Date:   Thu, 25 May 2017 14:59:16 -0700
From:   "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:     linux-kernel@...r.kernel.org
Cc:     mingo@...nel.org, jiangshanlai@...il.com, dipankar@...ibm.com,
        akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com,
        josh@...htriplett.org, tglx@...utronix.de, peterz@...radead.org,
        rostedt@...dmis.org, dhowells@...hat.com, edumazet@...gle.com,
        fweisbec@...il.com, oleg@...hat.com, bobby.prani@...il.com,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
        Ingo Molnar <mingo@...hat.com>
Subject: [PATCH tip/core/rcu 43/88] sched: Rely on synchronize_rcu_mult() de-duplication

The synchronize_rcu_mult() function now detects duplicate requests
for the same grace-period flavor and waits only once for each flavor.
This commit therefore removes the ugly #ifdef from sched_cpu_deactivate()
because synchronize_rcu_mult(call_rcu, call_rcu_sched) now does what
the #ifdef used to be needed for.

Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
Cc: Ingo Molnar <mingo@...hat.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
---
 kernel/sched/core.c | 8 +-------
 1 file changed, 1 insertion(+), 7 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 759f4bd52cd6..605564742de1 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -5849,15 +5849,9 @@ int sched_cpu_deactivate(unsigned int cpu)
 	 * users of this state to go away such that all new such users will
 	 * observe it.
 	 *
-	 * For CONFIG_PREEMPT we have preemptible RCU and its sync_rcu() might
-	 * not imply sync_sched(), so wait for both.
-	 *
 	 * Do sync before park smpboot threads to take care the rcu boost case.
 	 */
-	if (IS_ENABLED(CONFIG_PREEMPT))
-		synchronize_rcu_mult(call_rcu, call_rcu_sched);
-	else
-		synchronize_rcu();
+	synchronize_rcu_mult(call_rcu, call_rcu_sched);
 
 	if (!sched_smp_initialized)
 		return 0;
-- 
2.5.2