linux-kernel - Re: [PATCH 4/4] Btrfs: add basic DIO read/write support V3

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Message-Id: <20100513111136.6986e8cc.akpm@linux-foundation.org>
Date:	Thu, 13 May 2010 11:11:36 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Josef Bacik <josef@...hat.com>
Cc:	Christoph Hellwig <hch@...radead.org>, linux-btrfs@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH 4/4] Btrfs: add basic DIO read/write support V3

On Thu, 13 May 2010 14:01:37 -0400
Josef Bacik <josef@...hat.com> wrote:

> On Thu, May 13, 2010 at 11:26:39AM -0400, Christoph Hellwig wrote:
> > On Thu, May 13, 2010 at 11:31:45AM -0400, Josef Bacik wrote:
> > > AIO's aio_complete does kmap with KM_IRQ0/1 and it gets called in the same
> > > context as the btrfs completion handler, so if it's ok for aio_complete it
> > > should be ok for btrfs right?  Thanks,
> > 
> > aio_complete does a spin_lock_irqsave before that, which disables
> > interrupts on the local CPU.
> > 
> 
> Ok how about I just do
> 
> local_irq_disable()
> kmap(KM_IRQ0)
> local_irq_enable()
> 
> would that be acceptable?  Thanks,

yup.

local_irq_disable() (or local_irq_save())
kmap_atomic(KM_IRQx);
<stuff>
kunmap_atomic(KM_IRQx);
local_irq_enable() (or local_irq_restore()).

then perhaps flush_dcache_page().
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