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

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Message-ID: <20100513154336.GF27011@dhcp231-156.rdu.redhat.com>
Date:	Thu, 13 May 2010 11:43:36 -0400
From:	Josef Bacik <josef@...hat.com>
To:	Christoph Hellwig <hch@...radead.org>
Cc:	Josef Bacik <josef@...hat.com>, linux-btrfs@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	akpm@...ux-foundation.org
Subject: Re: [PATCH 4/4] Btrfs: add basic DIO read/write support V3

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 so looking at debug_kmap_atomic it seems that KM_IRQ0 is ok to use in all
cases, in_irq(), !irqs_disabled() and !in_interrupt(), so I should be safe.  If
you still don't like it, would something like this be acceptable?

if (in_interrupt() || irqs_disabled()) {
	if (in_irq())
		type = KM_IRQ0;
	else if (!irqs_disabled())
		type = KM_SOFTIRQ0;
	else
		type = KM_IRQ0;
} else {
	type = KM_USER0;
}

Hrm, you'd think somebody would have had this problem before and already come up
with a nice helper, oh well.  Thanks,

Josef
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