[PATCH] next_timer_interrupt: simpler overflow handling

• To: Linux Kernel Mailing List <[email protected]>
• Subject: [PATCH] next_timer_interrupt: simpler overflow handling
• From: Keir Fraser <[email protected]>
• Date: Thu, 13 Jul 2006 09:54:38 +0100
• Cc: [email protected], Zachary Amsden <[email protected]>, Keir Fraser <[email protected]>
• Sender: [email protected]

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 <[email protected]>

Attachment: fix-next-timer-interrupt.patch
Description: Binary data

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