hrtimer: catch expired CLOCK_REALTIME timers early

A CLOCK_REALTIME timer, which has an absolute expiry time less than
the clock realtime offset calls with a negative delta into the clock
events code and triggers the WARN_ON() there.

This is a false positive and needs to be prevented. Check the result
of timer->expires - timer->base->offset right away and return -ETIME
right away.

Thanks to Frans Pop, who reported the problem and tested the fixes.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Frans Pop <elendil@planet.nl>

diff --git a/kernel/hrtimer.c b/kernel/hrtimer.c
index c2893af..98bee01 100644 (file)
--- a/kernel/hrtimer.c
+++ b/kernel/hrtimer.c
@@ -442,6 +442,8 @@ static int hrtimer_reprogram(struct hrtimer *timer,
        ktime_t expires = ktime_sub(timer->expires, base->offset);
        int res;
 
+       WARN_ON_ONCE(timer->expires.tv64 < 0);
+
        /*
         * When the callback is running, we do not reprogram the clock event
         * device. The timer callback is either running on a different CPU or
@@ -452,6 +454,15 @@ static int hrtimer_reprogram(struct hrtimer *timer,
        if (hrtimer_callback_running(timer))
                return 0;
 
+       /*
+        * CLOCK_REALTIME timer might be requested with an absolute
+        * expiry time which is less than base->offset. Nothing wrong
+        * about that, just avoid to call into the tick code, which
+        * has now objections against negative expiry values.
+        */
+       if (expires.tv64 < 0)
+               return -ETIME;
+
        if (expires.tv64 >= expires_next->tv64)
                return 0;