[PATCH 17/45] time/clocksource: Use get/put_online_cpus_atomic() toprevent CPU offline

From: Srivatsa S. Bhat
Date: Sun Jun 23 2013 - 09:45:19 EST

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@xxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@xxxxxxxxxxxxxxxxxx>

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();
if (!watchdog_running)
goto out;
@@ -329,6 +331,7 @@ static void clocksource_watchdog(unsigned long data)
add_timer_on(&watchdog_timer, next_cpu);
+ 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. */
spin_unlock_irqrestore(&watchdog_lock, flags);
+ put_online_cpus_atomic();

static void clocksource_dequeue_watchdog(struct clocksource *cs)

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