Gitweb:
http://git.kernel.org/git/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=6ffc787a4492ac627315aaeafdfdc0a5c3028582
Commit: 6ffc787a4492ac627315aaeafdfdc0a5c3028582
Parent: 82f560874e88bd1fd8c98a6254d65a1dffab3876
Author: David Fries <[EMAIL PROTECTED]>
AuthorDate: Wed Feb 6 01:38:04 2008 -0800
Committer: Linus Torvalds <[EMAIL PROTECTED]>
CommitDate: Wed Feb 6 10:41:10 2008 -0800
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.
[EMAIL PROTECTED]: partially clean up the macro maze]
Signed-off-by: David Fries <[EMAIL PROTECTED]>
Cc: "H. Peter Anvin" <[EMAIL PROTECTED]>
Cc: Ingo Molnar <[EMAIL PROTECTED]>
Cc: Thomas Gleixner <[EMAIL PROTECTED]>
Signed-off-by: Andrew Morton <[EMAIL PROTECTED]>
Signed-off-by: Linus Torvalds <[EMAIL PROTECTED]>
---
include/linux/acct.h | 4 ++++
kernel/time.c | 11 +++++++++--
2 files changed, 13 insertions(+), 2 deletions(-)
diff --git a/include/linux/acct.h b/include/linux/acct.h
index 302eb72..e8cae54 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 4064c05..be5c8cb 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
-
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