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Date: Thu, 19 May 2011 11:05:26 -0700
From: Greg KH <gregkh@suse.de>
To: linux-kernel@vger.kernel.org, stable@kernel.org
Cc: stable-review@kernel.org, torvalds@linux-foundation.org,
        akpm@linux-foundation.org, alan@lxorguk.ukuu.org.uk,
        John Stultz <johnstul@us.ibm.com>,
        Thomas Gleixner <tglx@linutronix.de>
Subject: [58/71] clocksource: Install completely before selecting
In-Reply-To: <20110519180626.GA16555@kroah.com>
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2.6.38-stable review patch.  If anyone has any objections, please let us know.

------------------

From: john stultz <johnstul@us.ibm.com>

commit e05b2efb82596905ebfe88e8612ee81dec9b6592 upstream.

Christian Hoffmann reported that the command line clocksource override
with acpi_pm timer fails:

 Kernel command line: <SNIP> clocksource=acpi_pm
 hpet clockevent registered
 Switching to clocksource hpet
 Override clocksource acpi_pm is not HRT compatible.
 Cannot switch while in HRT/NOHZ mode.

The watchdog code is what enables CLOCK_SOURCE_VALID_FOR_HRES, but we
actually end up selecting the clocksource before we enqueue it into
the watchdog list, so that's why we see the warning and fail to switch
to acpi_pm timer as requested. That's particularly bad when we want to
debug timekeeping related problems in early boot.

Put the selection call last.

Reported-by: Christian Hoffmann <email@christianhoffmann.info>
Signed-off-by: John Stultz <johnstul@us.ibm.com>
Link: http://lkml.kernel.org/r/%3C1304558210.2943.24.camel%40work-vm%3E
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

---
 kernel/time/clocksource.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

--- a/kernel/time/clocksource.c
+++ b/kernel/time/clocksource.c
@@ -685,8 +685,8 @@ int __clocksource_register_scale(struct
 	/* Add clocksource to the clcoksource list */
 	mutex_lock(&clocksource_mutex);
 	clocksource_enqueue(cs);
-	clocksource_select();
 	clocksource_enqueue_watchdog(cs);
+	clocksource_select();
 	mutex_unlock(&clocksource_mutex);
 	return 0;
 }
@@ -706,8 +706,8 @@ int clocksource_register(struct clocksou
 
 	mutex_lock(&clocksource_mutex);
 	clocksource_enqueue(cs);
-	clocksource_select();
 	clocksource_enqueue_watchdog(cs);
+	clocksource_select();
 	mutex_unlock(&clocksource_mutex);
 	return 0;
 }


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