From: Andrew Morton <akpm@digeo.com>
To: Jens Axboe <axboe@suse.de>
Cc: tim@physik3.uni-rostock.de, linux-kernel@vger.kernel.org
Subject: Re: 2.5.64 and jiffies wrap
Date: Fri, 7 Mar 2003 04:15:58 -0800 [thread overview]
Message-ID: <20030307041558.6112425c.akpm@digeo.com> (raw)
In-Reply-To: <20030307130504.GA903@suse.de>
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.
next prev parent reply other threads:[~2003-03-07 12:05 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2003-03-07 13:05 Jens Axboe
2003-03-07 12:15 ` Andrew Morton [this message]
2003-03-07 13:20 ` Jens Axboe
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