[PATCH] posix timers: fix normalization problem

(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>

1 files changed, 3 insertions, 14 deletions

diff --git a/kernel/posix-timers.c b/kernel/posix-timers.c
index 5b7b473..10b2ad7 100644
--- a/kernel/posix-timers.c
+++ b/kernel/posix-timers.c
@@ -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();
 	}