[15/21] clocksource: Install completely before selecting

From: Greg KH
Date: Thu May 19 2011 - 14:28:12 EST

2.6.32-longterm review patch. If anyone has any objections, please let us know.


From: john stultz <johnstul@xxxxxxxxxx>

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@xxxxxxxxxxxxxxxxxxxxxx>
Signed-off-by: John Stultz <johnstul@xxxxxxxxxx>
Link: http://lkml.kernel.org/r/%3C1304558210.2943.24.camel%40work-vm%3E
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxx>

kernel/time/clocksource.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

--- a/kernel/time/clocksource.c
+++ b/kernel/time/clocksource.c
@@ -561,8 +561,8 @@ int clocksource_register(struct clocksou

- clocksource_select();
+ clocksource_select();
return 0;

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