linux-kernel - [PATCH v3 18/45] time/clocksource: Use get/put_online_cpus

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Date:	Fri, 28 Jun 2013 01:25:55 +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, David.Laight@...lab.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,
	John Stultz <john.stultz@...aro.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>
Subject: [PATCH v3 18/45] time/clocksource: 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: John Stultz <john.stultz@...aro.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@...ux.vnet.ibm.com>
---

 kernel/time/clocksource.c |    5 +++++
 1 file changed, 5 insertions(+)

diff --git a/kernel/time/clocksource.c b/kernel/time/clocksource.c
index e713ef7..c4bbc25 100644
--- a/kernel/time/clocksource.c
+++ b/kernel/time/clocksource.c
@@ -30,6 +30,7 @@
 #include <linux/sched.h> /* for spin_unlock_irq() using preempt_count() m68k */
 #include <linux/tick.h>
 #include <linux/kthread.h>
+#include <linux/cpu.h>
 
 #include "tick-internal.h"
 
@@ -252,6 +253,7 @@ static void clocksource_watchdog(unsigned long data)
 	int64_t wd_nsec, cs_nsec;
 	int next_cpu, reset_pending;
 
+	get_online_cpus_atomic();
 	spin_lock(&watchdog_lock);
 	if (!watchdog_running)
 		goto out;
@@ -329,6 +331,7 @@ static void clocksource_watchdog(unsigned long data)
 	add_timer_on(&watchdog_timer, next_cpu);
 out:
 	spin_unlock(&watchdog_lock);
+	put_online_cpus_atomic();
 }
 
 static inline void clocksource_start_watchdog(void)
@@ -367,6 +370,7 @@ static void clocksource_enqueue_watchdog(struct clocksource *cs)
 {
 	unsigned long flags;
 
+	get_online_cpus_atomic();
 	spin_lock_irqsave(&watchdog_lock, flags);
 	if (cs->flags & CLOCK_SOURCE_MUST_VERIFY) {
 		/* cs is a clocksource to be watched. */
@@ -386,6 +390,7 @@ static void clocksource_enqueue_watchdog(struct clocksource *cs)
 	/* Check if the watchdog timer needs to be started. */
 	clocksource_start_watchdog();
 	spin_unlock_irqrestore(&watchdog_lock, flags);
+	put_online_cpus_atomic();
 }
 
 static void clocksource_dequeue_watchdog(struct clocksource *cs)

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