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

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Message-ID: <20080226204943.GD14350@elte.hu>
Date:	Tue, 26 Feb 2008 21:49:43 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	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()


* 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.

	Ingo
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