[PATCH] next_timer_interrupt: simpler overflow handling

[Keir Fraser <Keir.Fraser@cl.cam.ac.uk>]

Having seen the patch applied to 2.6.17 to fix the overflowing 
comparison in next_timer_interrupt() it occurred to me that a much 
simpler fix is to not set hr_expires to MAX_JIFFY_OFFSET. It's way 
further out from jiffies than necessary, which is why it's caused 
problems. I instead propose that we initialise it to LONG_MAX>>1, just 
as we already do for the non-hr expires variable. This will allow safe 
comparison with any timer value in the range jiffies+/-(LONG_MAX>>1) 
which is plenty of range around jiffies (+/- 12 days if HZ=1000 and 
long is 32 bits).

The advantages are simpler code, and uniform initialisation of expires 
and hr_expires variables.

 -- Keir

Replace a fix for a comparison overflow in next_timer_interrupt() with 
a simpler alternative. We can be sure that the interesting range of 
timer values around jiffies is safe to compare with 
jiffies+(LONG_MAX>>1), unlike jiffies+MAX_JIFFY_OFFSET.

Signed-off-by: Keir Fraser <keir@xensource.com>

Attachment: fix-next-timer-interrupt.patch
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