From: Jens Axboe <axboe@suse.de>
To: Andrew Morton <akpm@digeo.com>
Cc: tim@physik3.uni-rostock.de, linux-kernel@vger.kernel.org
Subject: Re: 2.5.64 and jiffies wrap
Date: Fri, 7 Mar 2003 14:20:48 +0100 [thread overview]
Message-ID: <20030307132048.GC903@suse.de> (raw)
In-Reply-To: <20030307041558.6112425c.akpm@digeo.com>
On Fri, Mar 07 2003, Andrew Morton wrote:
> Jens Axboe <axboe@suse.de> wrote:
> >
> > Hi,
> >
> > The patch doesn't look right, why is INITIAL_JIFFIES being cast to
> > unsigned int? This breaks x86_64 at least.
> >
> > ...
> > -#define INITIAL_JIFFIES ((unsigned int) (-300*HZ))
>
> This sets the initial jiffies value to 0x00000000fffb6c20, which can trigger
> 32-bit wraparound bugs: if some random jiffy counter wraps from
> 0x00000000ffffffff to 0x0000000000000000 then things fail.
>
> davem was bitten by at least one such bug in the qlogicfc driver. It would
> have caused 64-bit machines to fail after 49 days.
>
> It turns out that it is more valuable to test for this than to test for
> 64-bit wraparound bugs.
Ok makes sense, I thought the point was just to test for jiffies wrap.
Anyways, the patch breaks boot on x86_64 here.
--
Jens Axboe
prev parent reply other threads:[~2003-03-07 12:12 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2003-03-07 13:05 2.5.64 and jiffies wrap Jens Axboe
2003-03-07 12:15 ` Andrew Morton
2003-03-07 13:20 ` Jens Axboe [this message]
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