linux-kernel - Re: [PATCH 002 of 2] md: Improve the is_mddev

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Message-ID: <Pine.LNX.4.61.0705101143540.32349@yvahk01.tjqt.qr>
Date:	Thu, 10 May 2007 11:48:48 +0200 (MEST)
From:	Jan Engelhardt <jengelh@...ux01.gwdg.de>
To:	NeilBrown <neilb@...e.de>
cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-raid@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 002 of 2] md: Improve the is_mddev_idle test


On May 10 2007 16:22, NeilBrown wrote:
>
>diff .prev/drivers/md/md.c ./drivers/md/md.c
>--- .prev/drivers/md/md.c	2007-05-10 15:51:54.000000000 +1000
>+++ ./drivers/md/md.c	2007-05-10 16:05:10.000000000 +1000
>@@ -5095,7 +5095,7 @@ static int is_mddev_idle(mddev_t *mddev)
> 		 *
> 		 * Note: the following is an unsigned comparison.
> 		 */
>-		if ((curr_events - rdev->last_events + 4096) > 8192) {
>+		if ((long)curr_events - (long)rdev->last_events > 4096) {
> 			rdev->last_events = curr_events;
> 			idle = 0;
> 		}

What did really change? Unless I am seriously mistaken,

    curr_events - last_evens + 4096 > 8192

is mathematically equivalent to

    curr_events - last_evens        > 4096

The casting to (long) may however force a signed comparison which turns
things quite upside down, and the comment does not apply anymore.


	Jan
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