clockevents: prevent endless loop in tick_handle_periodic()

tick_handle_periodic() can lock up hard when a one shot clock event
device is used in combination with jiffies clocksource.

Avoid an endless loop issue by requiring that a highres valid
clocksource be installed before we call tick_periodic() in a loop when
using ONESHOT mode. The result is we will only increment jiffies once
per interrupt until a continuous hardware clocksource is available.

Without this, we can run into a endless loop, where each cycle through
the loop, jiffies is updated which increments time by tick_period or
more (due to clock steering), which can cause the event programming to
think the next event was before the newly incremented time and fail
causing tick_periodic() to be called again and the whole process loops
forever.

[ Impact: prevent hard lock up ]

Signed-off-by: John Stultz <johnstul@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: stable@kernel.org

1 files changed, 11 insertions, 1 deletions

diff --git a/kernel/time/tick-common.c b/kernel/time/tick-common.c
index 21a5ca849514..83c4417b6a3c 100644
--- a/kernel/time/tick-common.c
+++ b/kernel/time/tick-common.c
@@ -93,7 +93,17 @@ void tick_handle_periodic(struct clock_event_device *dev)
         for (;;) {
                 if (!clockevents_program_event(dev, next, ktime_get()))
                         return;
-                tick_periodic(cpu);
+                /*
+                 * Have to be careful here. If we're in oneshot mode,
+                 * before we call tick_periodic() in a loop, we need
+                 * to be sure we're using a real hardware clocksource.
+                 * Otherwise we could get trapped in an infinite
+                 * loop, as the tick_periodic() increments jiffies,
+                 * when then will increment time, posibly causing
+                 * the loop to trigger again and again.
+                 */
+                if (timekeeping_valid_for_hres())
+                        tick_periodic(cpu);
                 next = ktime_add(next, tick_period);
         }
 }