Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754750AbYHTC3T (ORCPT ); Tue, 19 Aug 2008 22:29:19 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752374AbYHTC3K (ORCPT ); Tue, 19 Aug 2008 22:29:10 -0400 Received: from e1.ny.us.ibm.com ([32.97.182.141]:36390 "EHLO e1.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752175AbYHTC3J (ORCPT ); Tue, 19 Aug 2008 22:29:09 -0400 Subject: [PATCH] fix adjtimex() freq return error From: john stultz To: Andrew Morton Cc: Roman Zippel , Martin Ziegler , lkml Content-Type: text/plain Date: Tue, 19 Aug 2008 19:29:06 -0700 Message-Id: <1219199346.6276.5.camel@localhost> Mime-Version: 1.0 X-Mailer: Evolution 2.22.3.1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2304 Lines: 56 Martin Ziegler reported a bug in adjtimex(), where odd positive frequencies are reduced by 1 while negative values are correct. See http://bugzilla.kernel.org/show_bug.cgi?id=11370 for details The issue was introduced in the following commit that increased time_freq to a 64bit value and increased its resolution: http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commitdiff;h=074b3b87941c99bc0ce35385b5817924b1ed0c23;hp=eea83d896e318bda54be2d2770d2c5d6668d11db The problem is how we convert from our internal high res value back to userland. Instead of dividing, we shift, then mult, then shift again, causing the slight error seen in the bug. I don't think adjtimex() is a terribly hot path, so this patch simply uses div_s64() to convert back to the external resolution and removes the unused shift defines to resolve the issue. Signed-off-by: John Stultz Index: 2.6-git/kernel/time/ntp.c =================================================================== --- 2.6-git.orig/kernel/time/ntp.c +++ 2.6-git/kernel/time/ntp.c @@ -402,9 +402,7 @@ int do_adjtimex(struct timex *txc) if (!(time_status & STA_NANO)) txc->offset /= NSEC_PER_USEC; } - txc->freq = shift_right((s32)(time_freq >> PPM_SCALE_INV_SHIFT) * - (s64)PPM_SCALE_INV, - NTP_SCALE_SHIFT); + txc->freq = div_s64(time_freq, PPM_SCALE); txc->maxerror = time_maxerror; txc->esterror = time_esterror; txc->status = time_status; Index: 2.6-git/include/linux/timex.h =================================================================== --- 2.6-git.orig/include/linux/timex.h +++ 2.6-git/include/linux/timex.h @@ -82,9 +82,6 @@ */ #define SHIFT_USEC 16 /* frequency offset scale (shift) */ #define PPM_SCALE (NSEC_PER_USEC << (NTP_SCALE_SHIFT - SHIFT_USEC)) -#define PPM_SCALE_INV_SHIFT 20 -#define PPM_SCALE_INV ((1ll << (PPM_SCALE_INV_SHIFT + NTP_SCALE_SHIFT)) / \ - PPM_SCALE + 1) #define MAXPHASE 500000000l /* max phase error (ns) */ #define MAXFREQ 500000 /* max frequency error (ns/s) */ -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/