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authorLinus Torvalds <torvalds@linux-foundation.org>2008-12-04 21:40:29 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2008-12-04 21:40:29 -0800
commit4857339d7c01cd81ce8872da2d1f9183b07b1c87 (patch)
tree49d311b8bd623810822106a706f9db886c6ffb07
parent0efcafb0fb7a163999a8821e8a5e7792fca90a2d (diff)
parent6c9bacb41c10ba84ff68f238e234d96f35fb64f7 (diff)
Merge branch 'timers-fixes-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip
* '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
-rw-r--r--kernel/posix-cpu-timers.c2
-rw-r--r--kernel/time/timekeeping.c22
2 files changed, 23 insertions, 1 deletions
diff --git a/kernel/posix-cpu-timers.c b/kernel/posix-cpu-timers.c
index 895337b16a2..4e5288a831d 100644
--- a/kernel/posix-cpu-timers.c
+++ b/kernel/posix-cpu-timers.c
@@ -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:
diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index e7acfb482a6..fa05e88aa76 100644
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -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.
*/