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[PATCH] posix timers: fix normalization problem

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(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.)

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 <george@mvista.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
This commit is contained in:
George Anzinger 2005-07-28 21:16:16 -07:00 committed by Linus Torvalds
parent a2d76bd8fa
commit 78fa74a23b
1 changed files with 3 additions and 14 deletions
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17
kernel/posix-timers.c
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@ -896,21 +896,10 @@ static int adjust_abs_time(struct k_clock *clock, struct timespec *tp,
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();
}