Commit 36374583 authored Aug 06, 2016 by Kyle Walker Committed by John Stultz Aug 31, 2016

clocksource: Defer override invalidation unless clock is unstable



Clocksources don't get the VALID_FOR_HRES flag until they have been
checked by a watchdog. However, when using an override, the
clocksource_select logic will clear the override value if the
clocksource is not marked VALID_FOR_HRES during that inititial check.
When using the boot arguments clocksource=<foo>, this selection can
run before the watchdog, and can cause the override to be incorrectly
cleared.

To address this condition, the override_name is only invalidated for
unstable clocksources. Otherwise, the override is left intact until after
the watchdog has validated the clocksource as stable/unstable.

Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Richard Cochran <richardcochran@gmail.com>
Cc: Prarit Bhargava <prarit@redhat.com>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Signed-off-by: Kyle Walker <kwalker@redhat.com>
Signed-off-by: John Stultz <john.stultz@linaro.org>

parent b4d90e9f

kernel/time/clocksource.c

+12 −3

Original line number	Diff line number	Diff line
		@@ -600,9 +600,18 @@ static void __clocksource_select(bool skipcur)
		*/
		if (!(cs->flags & CLOCK_SOURCE_VALID_FOR_HRES) && oneshot) {
		/* Override clocksource cannot be used. */
		pr_warn("Override clocksource %s is not HRT compatible - cannot switch while in HRT/NOHZ mode\n",
		if (cs->flags & CLOCK_SOURCE_UNSTABLE) {
		pr_warn("Override clocksource %s is unstable and not HRT compatible - cannot switch while in HRT/NOHZ mode\n",
		cs->name);
		override_name[0] = 0;
		} else {
		/*
		* The override cannot be currently verified.
		* Deferring to let the watchdog check.
		*/
		pr_info("Override clocksource %s is not currently HRT compatible - deferring\n",
		cs->name);
		}
		} else
		/* Override clocksource can be used. */
		best = cs;

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