The patch titled
system timer: fix crash in <100Hz system timer
has been removed from the -mm tree. Its filename was
system-timer-fix-crash-in-100hz-system-timer.patch
This patch was dropped because it was merged into mainline or a subsystem tree
The current -mm tree may be found at http://userweb.kernel.org/~akpm/mmotm/
------------------------------------------------------
Subject: system timer: fix crash in <100Hz system timer
From: David Fries <david@xxxxxxxxx>
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@xxxxxxxxxxxxxxxxxxxx: partially clean up the macro maze]
Signed-off-by: David Fries <david@xxxxxxxxx>
Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/acct.h | 4 ++++
kernel/time.c | 11 +++++++++--
2 files changed, 13 insertions(+), 2 deletions(-)
diff -puN include/linux/acct.h~system-timer-fix-crash-in-100hz-system-timer include/linux/acct.h
--- a/include/linux/acct.h~system-timer-fix-crash-in-100hz-system-timer
+++ a/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 -puN kernel/time.c~system-timer-fix-crash-in-100hz-system-timer kernel/time.c
--- a/kernel/time.c~system-timer-fix-crash-in-100hz-system-timer
+++ a/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
_
Patches currently in -mm which might be from david@xxxxxxxxx are
origin.patch
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