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

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Message-Id: <20080226133715.d9cd32e7.akpm@linux-foundation.org>
Date:	Tue, 26 Feb 2008 13:37:15 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Ingo Molnar <mingo@...e.hu>
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()

On Tue, 26 Feb 2008 21:49:43 +0100 Ingo Molnar <mingo@...e.hu> 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.
> 

Sure.  But iirc we haven't had a need for this before.  Which is a bit odd.
 
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