Commit 78fa74a2 authored Jul 28, 2005 by George Anzinger Committed by Linus Torvalds Jul 28, 2005

[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>

parent a2d76bd8

kernel/posix-timers.c

+3 −14

Original line number	Diff line number	Diff line
		@@ -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();
		}

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