linux-kernel - Re: [PATCH v2 15/26] block: Add bio_copy

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Message-ID: <20120921000945.GK5519@google.com>
Date:	Thu, 20 Sep 2012 17:09:45 -0700
From:	Kent Overstreet <koverstreet@...gle.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	linux-bcache@...r.kernel.org, linux-kernel@...r.kernel.org,
	dm-devel@...hat.com, axboe@...nel.dk, neilb@...e.de
Subject: Re: [PATCH v2 15/26] block: Add bio_copy_data()

On Thu, Sep 20, 2012 at 05:06:32PM -0700, Tejun Heo wrote:
> Hello,
> 
> On Mon, Sep 10, 2012 at 05:22:26PM -0700, Kent Overstreet wrote:
> > +void bio_copy_data(struct bio *dst, struct bio *src)
> > +{
> ...
> > +		src_p = kmap_atomic(src_bv->bv_page);
> > +		dst_p = kmap_atomic(dst_bv->bv_page);
> > +
> > +		memcpy(dst_p + dst_bv->bv_offset,
> > +		       src_p + src_bv->bv_offset,
> > +		       bytes);
> > +
> > +		kunmap_atomic(dst_p);
> > +		kunmap_atomic(src_p);
> 
> Wrap these in preempt_disable/enable() to allow the function to be
> called from any context?

I checked the implementation of kmap_atomic(), it already does
preempt_disable() so it's safe in process context - if I understand
correctly it needs local_irq_save()/restore() to be safe in any context
and I figured calling this from irq context is not the norm so that
should be the caller's responsibility.
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