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| author | David Fries <david@fries.net> | 2008-02-06 01:38:04 -0800 |
|---|---|---|
| committer | Linus Torvalds <torvalds@woody.linux-foundation.org> | 2008-02-06 10:41:10 -0800 |
| commit | 6ffc787a4492ac627315aaeafdfdc0a5c3028582 (patch) | |
| tree | bb557076ead94695cd148c4b7b065d44e77e62a3 /kernel/time.c | |
| parent | 82f560874e88bd1fd8c98a6254d65a1dffab3876 (diff) | |
| download | lwn-6ffc787a4492ac627315aaeafdfdc0a5c3028582.tar.gz lwn-6ffc787a4492ac627315aaeafdfdc0a5c3028582.zip | |
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>
Diffstat (limited to 'kernel/time.c')
| -rw-r--r-- | kernel/time.c | 11 |
1 files changed, 9 insertions, 2 deletions
diff --git a/kernel/time.c b/kernel/time.c index 4064c0566e77..be5c8cb93582 100644 --- a/kernel/time.c +++ b/kernel/time.c @@ -566,7 +566,11 @@ 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)); @@ -599,7 +603,12 @@ EXPORT_SYMBOL(clock_t_to_jiffies); u64 jiffies_64_to_clock_t(u64 x) { #if (TICK_NSEC % (NSEC_PER_SEC / USER_HZ)) == 0 +# 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, @@ -611,7 +620,6 @@ u64 jiffies_64_to_clock_t(u64 x) #endif return x; } - EXPORT_SYMBOL(jiffies_64_to_clock_t); u64 nsec_to_clock_t(u64 x) @@ -646,7 +654,6 @@ u64 get_jiffies_64(void) } while (read_seqretry(&xtime_lock, seq)); return ret; } - EXPORT_SYMBOL(get_jiffies_64); #endif |