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.
Signed-off-by: Kyle Walker <kwal...@redhat.com>
Cc: John Stultz <john.stu...@linaro.org>
Cc: Thomas Gleixner <t...@linutronix.de>
Cc: Martin Schwidefsky <schwidef...@de.ibm.com>
Cc: linux-kernel@vger.kernel.org
---
Notes:
Changes from v1:
* Altered changelog description, many thanks to John Stultz for the assist!
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 56ece14..4c1bb2a 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;
--
2.5.5
