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authorDavid Fries <david@fries.net>2008-02-06 01:38:04 -0800
committerLinus Torvalds <torvalds@woody.linux-foundation.org>2008-02-06 10:41:10 -0800
commit6ffc787a4492ac627315aaeafdfdc0a5c3028582 (patch)
treebb557076ead94695cd148c4b7b065d44e77e62a3
parent82f560874e88bd1fd8c98a6254d65a1dffab3876 (diff)
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>
-rw-r--r--include/linux/acct.h4
-rw-r--r--kernel/time.c11
2 files changed, 13 insertions, 2 deletions
diff --git a/include/linux/acct.h b/include/linux/acct.h
index 302eb727ecb..e8cae54e8d8 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
+# 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 4064c0566e7..be5c8cb9358 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