Re: patch: highmem zero-bounce

From: Jens Axboe (
Date: Wed Jun 27 2001 - 11:27:45 EST

On Wed, Jun 27 2001, Andrea Arcangeli wrote:
> On Tue, Jun 26, 2001 at 06:22:15PM +0200, Jens Axboe wrote:
> > Hi,
> >
> > I updated the patches to 2.4.6-pre5, and removed the zone-dma32
> > addition. This means that machines with > 4GB of RAM will need to go all
> good, we can relax the ZONE_NORMAL later, that's a separate problem with
> skipping the bounces.


> I can see one mm corruption race condition in the patch, you missed
> nested irq in the for kmap_irq_bh (PIO). You must _always_
> __cli/__save_flags before accessing the KMAP_IRQ_BH slot, in case the
> remapping is required (so _only_ when the page is in the highmem zone).
> Otherwise memory corruption will happen when the race triggers (for
> example two ide disks in PIO mode doing I/O at the same time connected
> to different irq sources).

Ah yes, my bad. This requires some moving around, I'll post an updated
patch later tonight. Thanks!

Jens Axboe

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