On Sat, 5 Jan 2008 16:16:55 -0600 David Fries <[EMAIL PROTECTED]> wrote:
> 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. > > Signed-off-by: David Fries <[EMAIL PROTECTED]> > > -- > David Fries <[EMAIL PROTECTED]> > http://fries.net/~david/ (PGP encryption key available) > > > diff --git a/include/linux/acct.h b/include/linux/acct.h > index 302eb72..86b848d 100644 > --- a/include/linux/acct.h > +++ b/include/linux/acct.h > @@ -173,7 +173,11 @@ typedef struct acct acct_t; > static inline u32 jiffies_to_AHZ(unsigned long x) > { > #if (TICK_NSEC % (NSEC_PER_SEC / AHZ)) == 0 > - return x / (HZ / AHZ); > + #if HZ < AHZ > + return x * (AHZ / HZ); > + #else > + return x / (HZ / AHZ); > + #endif > #else > u64 tmp = (u64)x * TICK_NSEC; > do_div(tmp, (NSEC_PER_SEC / AHZ)); > diff --git a/kernel/time.c b/kernel/time.c > index 09d3c45..23af26f 100644 > --- a/kernel/time.c > +++ b/kernel/time.c > @@ -565,7 +565,11 @@ EXPORT_SYMBOL(jiffies_to_timeval); > clock_t jiffies_to_clock_t(long x) > { > #if (TICK_NSEC % (NSEC_PER_SEC / USER_HZ)) == 0 > + #if HZ < USER_HZ > + return x * (USER_HZ / HZ); > + #else > return x / (HZ / USER_HZ); > + #endif > #else > u64 tmp = (u64)x * TICK_NSEC; > do_div(tmp, (NSEC_PER_SEC / USER_HZ)); > @@ -598,7 +602,12 @@ EXPORT_SYMBOL(clock_t_to_jiffies); > u64 jiffies_64_to_clock_t(u64 x) > { > #if (TICK_NSEC % (NSEC_PER_SEC / USER_HZ)) == 0 > - do_div(x, HZ / USER_HZ); > + #if HZ < USER_HZ > + x *= USER_HZ; > + do_div(x, HZ); > + #else > + do_div(x, HZ / USER_HZ); > + #endif > #else > /* > * There are better ways that don't overflow early, Alas, I get 100% rejects due to conflicting changes from Peter's avoid-overflows-in-kernel-timec.patch. Peter, did that patch propagate this failure, or might it have happily fixed it? -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
