clocksource: Install completely before selecting

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>
Cc: stable@kernel.org # 32...
Link: http://lkml.kernel.org/r/%3C1304558210.2943.24.camel%40work-vm%3E
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

diff --git a/kernel/time/clocksource.c b/kernel/time/clocksource.c
index 6519cf62d9cd99706bb59ce0e5776733396b22ab..0e17c10f8a9daae8fdd8c665d69788670549b1c0 100644 (file)
--- a/kernel/time/clocksource.c
+++ b/kernel/time/clocksource.c
@@ -685,8 +685,8 @@ int __clocksource_register_scale(struct clocksource *cs, u32 scale, u32 freq)
        /* 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 clocksource *cs)
 
        mutex_lock(&clocksource_mutex);
        clocksource_enqueue(cs);
-       clocksource_select();
        clocksource_enqueue_watchdog(cs);
+       clocksource_select();
        mutex_unlock(&clocksource_mutex);
        return 0;
 }