[patch-rt 2/5] commit 6626bff24578753808c8b5bd4f1619e14e980f0fAuthor: Thomas Gleixner <tglx@linutronix.de> Date: Sun Jan 2511:31:36 2009 +0100

[Thomas Gleixner]

    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@xxxxxxxxxxxxx>

---
 kernel/hrtimer.c |    7 +++++++
 1 file changed, 7 insertions(+)

Index: linux-2.6.26.8/kernel/hrtimer.c
===================================================================
--- linux-2.6.26.8.orig/kernel/hrtimer.c
+++ linux-2.6.26.8/kernel/hrtimer.c
@@ -520,6 +520,13 @@ static void hrtimer_force_reprogram(stru
 			continue;
 		timer = rb_entry(base->first, struct hrtimer, node);
 		expires = ktime_sub(timer->expires, 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;
 	}


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