From 36374583f9084cdab4b5dcf5521a3ce55bebb9fa Mon Sep 17 00:00:00 2001 From: Kyle Walker Date: Sat, 6 Aug 2016 12:07:30 -0400 Subject: [PATCH] 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=, 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 Cc: Ingo Molnar Cc: Richard Cochran Cc: Prarit Bhargava Cc: Martin Schwidefsky Signed-off-by: Kyle Walker Signed-off-by: John Stultz --- kernel/time/clocksource.c | 15 ++++++++++++--- 1 file changed, 12 insertions(+), 3 deletions(-) diff --git a/kernel/time/clocksource.c b/kernel/time/clocksource.c index 6a5a310a1a53..7e4fad75acaa 100644 --- a/kernel/time/clocksource.c +++ b/kernel/time/clocksource.c @@ -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", - cs->name); - override_name[0] = 0; + 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;