From: David Fries <david@fries.net>
Date: Wed, 6 Feb 2008 09:38:04 +0000 (-0800)
Subject: system timer: fix crash in <100Hz system timer
X-Git-Tag: v2.6.25-rc1~665
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=6ffc787a4492ac627315aaeafdfdc0a5c3028582;p=pandora-kernel.git

system timer: fix crash in <100Hz system timer

The kernel has a divide by zero crash when trying to run the system timer
less than 100Hz.  The problem is x/(HZ/USER_HZ) and related.  Now
x*(USER_HZ/HZ) will be used if HZ<USER_HZ.

I'm running the Linux kernel under qemu and went to run a slower system
timer to take less CPU (and battery) on the host.  I found that the kernel
paniced under emulation because of a divide by zero in three places.  Here
is the patch.  The base git was updated today 01-05-2008.  I went for a
20Hz system time by adding config HZ_20 etc to kernel/Kconfig.hz.  With
this patch I verified the system timer by looking at /proc/interrupts.

[akpm@linux-foundation.org: partially clean up the macro maze]
Signed-off-by: David Fries <david@fries.net>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
---

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