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From: Nick Piggin <nickpiggin@yahoo.com.au>
To: Ingo Molnar <mingo@elte.hu>
Subject: Re: 2.6.24-git: kmap_atomic() WARN_ON()
Date: Wed, 27 Feb 2008 10:49:34 +1100
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Cc: Andrew Morton <akpm@linux-foundation.org>, Jeff Garzik <jgarzik@pobox.com>,
       Thomas Gleixner <tglx@linutronix.de>,
       =?iso-8859-1?q?Bj=F6rn_Steinbrink?= <B.Steinbrink@gmx.de>,
       LKML <linux-kernel@vger.kernel.org>
References: <alpine.LFD.1.00.0802070054220.9204@apollo.tec.linutronix.de> <20080226101928.f6c16c66.akpm@linux-foundation.org> <20080226204943.GD14350@elte.hu>
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On Wednesday 27 February 2008 07:49, Ingo Molnar wrote:
> * Andrew Morton <akpm@linux-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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