linux-kernel - [PATCH tip/core/rcu 11/18] rcu: Stop excluding CPU hotplug in synchronize_sched

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Date:	Tue,  6 Oct 2015 09:29:30 -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,
	dvhart@...ux.intel.com, fweisbec@...il.com, oleg@...hat.com,
	bobby.prani@...il.com,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: [PATCH tip/core/rcu 11/18] rcu: Stop excluding CPU hotplug in synchronize_sched_expedited()

Now that synchronize_sched_expedited() uses IPIs, a hook in
rcu_sched_qs(), and the ->expmask field in the rcu_node combining
tree, it is no longer necessary to exclude CPU hotplug.  Any
races with CPU hotplug will be detected when attempting to send
the IPI.  This commit therefore removes the code excluding
CPU hotplug operations.

Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
---
 kernel/rcu/tree.c | 14 +-------------
 1 file changed, 1 insertion(+), 13 deletions(-)

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 57b83f6d5263..6885bfc9d2bf 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -3785,19 +3785,9 @@ void synchronize_sched_expedited(void)
 	/* Take a snapshot of the sequence number.  */
 	s = rcu_exp_gp_seq_snap(rsp);
 
-	if (!try_get_online_cpus()) {
-		/* CPU hotplug operation in flight, fall back to normal GP. */
-		wait_rcu_gp(call_rcu_sched);
-		atomic_long_inc(&rsp->expedited_normal);
-		return;
-	}
-	WARN_ON_ONCE(cpu_is_offline(raw_smp_processor_id()));
-
 	rnp = exp_funnel_lock(rsp, s);
-	if (rnp == NULL) {
-		put_online_cpus();
+	if (rnp == NULL)
 		return;  /* Someone else did our work for us. */
-	}
 
 	rcu_exp_gp_seq_start(rsp);
 	sync_sched_exp_select_cpus(rsp);
@@ -3805,8 +3795,6 @@ void synchronize_sched_expedited(void)
 
 	rcu_exp_gp_seq_end(rsp);
 	mutex_unlock(&rnp->exp_funnel_mutex);
-
-	put_online_cpus();
 }
 EXPORT_SYMBOL_GPL(synchronize_sched_expedited);
 
-- 
2.5.2

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