hrtimer: prevent negative expiry value after clock_was_set()

Impact: prevent false positive WARN_ON() in clockevents_program_event()

clock_was_set() changes the base->offset of CLOCK_REALTIME and
enforces the reprogramming of the clockevent device to expire timers
which are based on CLOCK_REALTIME. If the clock change is large enough
then the subtraction of the timer expiry value and base->offset can
become negative which triggers the warning in
clockevents_program_event().

Check the subtraction result and set a negative value to 0.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

1 files changed, 7 insertions, 0 deletions

diff --git a/kernel/hrtimer.c b/kernel/hrtimer.c
index 647a40e2fea1..f394d2a42ca3 100644
--- a/kernel/hrtimer.c
+++ b/kernel/hrtimer.c
@@ -501,6 +501,13 @@ static void hrtimer_force_reprogram(struct hrtimer_cpu_base *cpu_base)
                         continue;
                 timer = rb_entry(base->first, struct hrtimer, node);
                 expires = ktime_sub(hrtimer_get_expires(timer), base->offset);
+                /*
+                 * clock_was_set() has changed base->offset so the
+                 * result might be negative. Fix it up to prevent a
+                 * false positive in clockevents_program_event()
+                 */
+                if (expires.tv64 < 0)
+                        expires.tv64 = 0;
                 if (expires.tv64 < cpu_base->expires_next.tv64)
                         cpu_base->expires_next = expires;
         }