Commit-ID: 36374583f9084cdab4b5dcf5521a3ce55bebb9fa
Gitweb: http://git.kernel.org/tip/36374583f9084cdab4b5dcf5521a3ce55bebb9fa
Author: Kyle Walker <kwalker@xxxxxxxxxx>
AuthorDate: Sat, 6 Aug 2016 12:07:30 -0400
Committer: John Stultz <john.stultz@xxxxxxxxxx>
CommitDate: Wed, 31 Aug 2016 14:43:33 -0700
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@xxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Richard Cochran <richardcochran@xxxxxxxxx>
Cc: Prarit Bhargava <prarit@xxxxxxxxxx>
Cc: Martin Schwidefsky <schwidefsky@xxxxxxxxxx>
Signed-off-by: Kyle Walker <kwalker@xxxxxxxxxx>
Signed-off-by: John Stultz <john.stultz@xxxxxxxxxx>
---
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 6a5a310..7e4fad7 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;
--
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