Re: [Regression] Negative time on Acer Ferrari One with current-git

From: Thomas Gleixner
Date: Sun May 23 2010 - 02:41:28 EST

On Sat, 22 May 2010, Rafael J. Wysocki wrote:
> After reverting commit 64ce4c2f above things work again.
> To be precise, I reverted both commit 64ce4c2f and commit 6a867a3 (time:
> Remove xtime_cache), but since the symptoms continued to apprear after
> reverting the latter alone, it's quite clear that commit 64ce4c2f breaks things
> on this box.

I assume the cmos clock of this machine is not on UTC, right ? Does
the patch below fix the issue ?

@John: Can you please check the other users of timespec_add_safe() in
timekeeping as well ?



Subject: timekeeping: Fix timezone update
From: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Date: Sun, 23 May 2010 08:14:45 +0200

commit 64ce4c2f (time: Clean up warp_clock()) breaks the timezone
update in a very subtle way. To avoid the direct access to timekeeping
internals it adds the timezone delta to the current time with
timespec_add_safe(). This works nicely when the timezone delta is > 0.
If timezone delta is < 0 then the wrap check in timespec_add_safe()
triggers and timespec_add_safe() returns TIME_MAX and screws up
timekeeping completely.

This is not surprising as the comment above timespec_add_safe() says:
It's assumed that both values are valid (>= 0)

The function was created to avoid overflow issues when adding the
select() timeout to current time, where the above applies.

Add the timezone seconds adjustment directly.

Reported-by: Rafael J. Wysocki <rjw@xxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
kernel/time.c | 8 ++++----
1 file changed, 4 insertions(+), 4 deletions(-)

Index: linux-2.6/kernel/time.c
--- linux-2.6.orig/kernel/time.c
+++ linux-2.6/kernel/time.c
@@ -132,10 +132,10 @@ SYSCALL_DEFINE2(gettimeofday, struct tim
static inline void warp_clock(void)
- struct timespec delta, adjust;
- delta.tv_sec = sys_tz.tz_minuteswest * 60;
- delta.tv_nsec = 0;
- adjust = timespec_add_safe(current_kernel_time(), delta);
+ struct timespec adjust;
+ adjust = current_kernel_time();
+ adjust.tv_sec += sys_tz.tz_minuteswest * 60;

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