linux-kernel - [PATCH v2 16/45] tick-broadcast: Use get/put_online_cpus

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Message-ID: <20130625202813.16593.86718.stgit@srivatsabhat.in.ibm.com>
Date:	Wed, 26 Jun 2013 01:58:13 +0530
From:	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>
To:	tglx@...utronix.de, peterz@...radead.org, tj@...nel.org,
	oleg@...hat.com, paulmck@...ux.vnet.ibm.com, rusty@...tcorp.com.au,
	mingo@...nel.org, akpm@...ux-foundation.org, namhyung@...nel.org,
	walken@...gle.com, vincent.guittot@...aro.org, laijs@...fujitsu.com
Cc:	rostedt@...dmis.org, wangyun@...ux.vnet.ibm.com,
	xiaoguangrong@...ux.vnet.ibm.com, sbw@....edu, fweisbec@...il.com,
	zhong@...ux.vnet.ibm.com, nikunj@...ux.vnet.ibm.com,
	srivatsa.bhat@...ux.vnet.ibm.com, linux-pm@...r.kernel.org,
	linux-arch@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	Thomas Gleixner <tglx@...utronix.de>,
	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>
Subject: [PATCH v2 16/45] tick-broadcast: Use get/put_online_cpus_atomic() to
 prevent CPU offline

Once stop_machine() is gone from the CPU offline path, we won't be able
to depend on disabling preemption to prevent CPUs from going offline
from under us.

Use the get/put_online_cpus_atomic() APIs to prevent CPUs from going
offline, while invoking from atomic context.

Cc: Thomas Gleixner <tglx@...utronix.de>
Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@...ux.vnet.ibm.com>
---

 kernel/time/tick-broadcast.c |    8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/kernel/time/tick-broadcast.c b/kernel/time/tick-broadcast.c
index 9d96a54..1e4ac45 100644
--- a/kernel/time/tick-broadcast.c
+++ b/kernel/time/tick-broadcast.c
@@ -227,12 +227,14 @@ static void tick_do_broadcast(struct cpumask *mask)
  */
 static void tick_do_periodic_broadcast(void)
 {
+	get_online_cpus_atomic();
 	raw_spin_lock(&tick_broadcast_lock);
 
 	cpumask_and(tmpmask, cpu_online_mask, tick_broadcast_mask);
 	tick_do_broadcast(tmpmask);
 
 	raw_spin_unlock(&tick_broadcast_lock);
+	put_online_cpus_atomic();
 }
 
 /*
@@ -335,11 +337,13 @@ out:
  */
 void tick_broadcast_on_off(unsigned long reason, int *oncpu)
 {
+	get_online_cpus_atomic();
 	if (!cpumask_test_cpu(*oncpu, cpu_online_mask))
 		printk(KERN_ERR "tick-broadcast: ignoring broadcast for "
 		       "offline CPU #%d\n", *oncpu);
 	else
 		tick_do_broadcast_on_off(&reason);
+	put_online_cpus_atomic();
 }
 
 /*
@@ -505,6 +509,7 @@ static void tick_handle_oneshot_broadcast(struct clock_event_device *dev)
 	ktime_t now, next_event;
 	int cpu, next_cpu = 0;
 
+	get_online_cpus_atomic();
 	raw_spin_lock(&tick_broadcast_lock);
 again:
 	dev->next_event.tv64 = KTIME_MAX;
@@ -562,6 +567,7 @@ again:
 			goto again;
 	}
 	raw_spin_unlock(&tick_broadcast_lock);
+	put_online_cpus_atomic();
 }
 
 /*
@@ -756,6 +762,7 @@ void tick_broadcast_switch_to_oneshot(void)
 	struct clock_event_device *bc;
 	unsigned long flags;
 
+	get_online_cpus_atomic();
 	raw_spin_lock_irqsave(&tick_broadcast_lock, flags);
 
 	tick_broadcast_device.mode = TICKDEV_MODE_ONESHOT;
@@ -764,6 +771,7 @@ void tick_broadcast_switch_to_oneshot(void)
 		tick_broadcast_setup_oneshot(bc);
 
 	raw_spin_unlock_irqrestore(&tick_broadcast_lock, flags);
+	put_online_cpus_atomic();
 }
 
 

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