We found this (after a customer complained) and it is in the kernel.org
kernel. Seems that for CLOCK_MONOTONIC absolute timers and
clock_nanosleep calls both the request time and wall_to_monotonic are
subtracted prior to the normalize resulting in an overflow in the
existing normalize test. This causes the result to be shifted ~4
seconds ahead instead of ~2 seconds back in time. Patch is attached.
-
George Anzinger [email protected]
HRT (High-res-timers): http://sourceforge.net/projects/high-res-timers/
Source: MontaVista Software, Inc. George Anzinger <[email protected]>
Type: Defect Fix
Description:
The normalize code in posix-timers.c fails when the tv_nsec
member is ~1.2 seconds negative. This can happen on absolute
timers (and clock_nanosleeps) requested on CLOCK_MONOTONIC
(both the request time and wall_to_monotonic are subtracted
resulting in the possibility of a number close to -2 seconds.)
This fix uses the set_normalized_timespec() (which does not
have an overflow problem) to fix the problem and as a side
effect makes the code cleaner.
Signed-off-by: George Anzinger <[email protected]>
posix-timers.c | 17 +++--------------
1 files changed, 3 insertions(+), 14 deletions(-)
Index: linux-2.6.13-rc/kernel/posix-timers.c
===================================================================
--- linux-2.6.13-rc.orig/kernel/posix-timers.c
+++ linux-2.6.13-rc/kernel/posix-timers.c
@@ -915,21 +915,10 @@ static int adjust_abs_time(struct k_cloc
jiffies_64_f = get_jiffies_64();
}
/*
- * Take away now to get delta
+ * Take away now to get delta and normalize
*/
- oc.tv_sec -= now.tv_sec;
- oc.tv_nsec -= now.tv_nsec;
- /*
- * Normalize...
- */
- while ((oc.tv_nsec - NSEC_PER_SEC) >= 0) {
- oc.tv_nsec -= NSEC_PER_SEC;
- oc.tv_sec++;
- }
- while ((oc.tv_nsec) < 0) {
- oc.tv_nsec += NSEC_PER_SEC;
- oc.tv_sec--;
- }
+ set_normalized_timespec(&oc, oc.tv_sec - now.tv_sec,
+ oc.tv_nsec - now.tv_nsec);
}else{
jiffies_64_f = get_jiffies_64();
}
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