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Merge branch 'timers-fixes-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip

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* 'timers-fixes-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip:
  time: catch xtime_nsec underflows and fix them
  posix-cpu-timers: fix clock_gettime with CLOCK_PROCESS_CPUTIME_ID
This commit is contained in:
Linus Torvalds 2008-12-04 21:40:29 -08:00
commit 4857339d7c
2 changed files with 23 additions and 1 deletions
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2
kernel/posix-cpu-timers.c
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@ -311,7 +311,7 @@ static int cpu_clock_sample_group(const clockid_t which_clock,
struct task_cputime cputime;
thread_group_cputime(p, &cputime);
switch (which_clock) {
switch (CPUCLOCK_WHICH(which_clock)) {
default:
return -EINVAL;
case CPUCLOCK_PROF:

22
kernel/time/timekeeping.c
View file

@ -518,6 +518,28 @@ void update_wall_time(void)
/* correct the clock when NTP error is too big */
clocksource_adjust(offset);
/*
* Since in the loop above, we accumulate any amount of time
* in xtime_nsec over a second into xtime.tv_sec, its possible for
* xtime_nsec to be fairly small after the loop. Further, if we're
* slightly speeding the clocksource up in clocksource_adjust(),
* its possible the required corrective factor to xtime_nsec could
* cause it to underflow.
*
* Now, we cannot simply roll the accumulated second back, since
* the NTP subsystem has been notified via second_overflow. So
* instead we push xtime_nsec forward by the amount we underflowed,
* and add that amount into the error.
*
* We'll correct this error next time through this function, when
* xtime_nsec is not as small.
*/
if (unlikely((s64)clock->xtime_nsec < 0)) {
s64 neg = -(s64)clock->xtime_nsec;
clock->xtime_nsec = 0;
clock->error += neg << (NTP_SCALE_SHIFT - clock->shift);
}
/* store full nanoseconds into xtime after rounding it up and
* add the remainder to the error difference.
*/