linux-kernel - Re: 2.6.24-git: kmap_atomic() WARN

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Message-Id: <200802271049.35178.nickpiggin@yahoo.com.au>
Date:	Wed, 27 Feb 2008 10:49:34 +1100
From:	Nick Piggin <nickpiggin@...oo.com.au>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Jeff Garzik <jgarzik@...ox.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Björn Steinbrink <B.Steinbrink@....de>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: 2.6.24-git: kmap_atomic() WARN_ON()

On Wednesday 27 February 2008 07:49, Ingo Molnar wrote:
> * Andrew Morton <akpm@...ux-foundation.org> wrote:
> > > This is only being done to satisfy kmap_atomic's requirements, not
> > > libata's.
> > >
> > > I could add a "kmap lock" but that just seems silly.
> >
> > It's a bit sad to disable interupts across a memset (how big is it?)
> > just for the small proportion of cases which are accessing a highmem
> > page.
> >
> > What you could do is to add an `unsigned long *flags' arg to
> > ata_scsi_rbuf_get() and ata_scsi_rbuf_put(), and then, in
> > ata_scsi_rbuf_get() do
> >
> > 	if (PageHighmem(page))
> > 		local_irq_disable(*flags);
>
> it would be much nicer to attach the irq disabling to the object, not to
> some arbitrary place in the code.
>
> i.e. to introduce a kmap_atomic_irqsave(...,flags) and
> kunmap_atomic_irqrestore() API variant. _That_ then could be mapped by
> -rt to a non-irq disabling thing.

Yeah that is the right way to fix it, but that name implies that
interrupts are disabled for non-highmem pages too, which we don't
want. Can you think of a better one?

kmap_atomic_irq_safe maybe?

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