Re: 2.5.64 and jiffies wrap

Jens Axboe (
Fri, 7 Mar 2003 14:20:48 +0100

On Fri, Mar 07 2003, Andrew Morton wrote:
> Jens Axboe <> 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

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