[patch 29/38] hrtimer: catch expired CLOCK_REALTIME timers early

[Greg KH]

2.6.24-stable review patch.  If anyone has any objections, please let us
know.

------------------
From: Thomas Gleixner <tglx@xxxxxxxxxxxxx>

commit 63070a79ba482c274bad10ac8c4b587a3e011f2c

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@xxxxxxxxxxxxx>
Tested-by: Frans Pop <elendil@xxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxx>

---
 kernel/hrtimer.c |   11 +++++++++++
 1 file changed, 11 insertions(+)

--- a/kernel/hrtimer.c
+++ b/kernel/hrtimer.c
@@ -427,6 +427,8 @@ static int hrtimer_reprogram(struct hrti
 	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
@@ -437,6 +439,15 @@ static int hrtimer_reprogram(struct hrti
 	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;
 

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