linux-kernel - Re: [PATCH 04/15] ps3vram: Replace mutex by spinlock + list

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Date:	Mon, 11 May 2009 08:38:06 +0200 (CEST)
From:	Geert Uytterhoeven <Geert.Uytterhoeven@...ycom.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
cc:	benh@...nel.crashing.org, cbe-oss-dev@...abs.org,
	linux-kernel@...r.kernel.org,
	linux-fbdev-devel@...ts.sourceforge.net, jim@...n.com
Subject: Re: [PATCH 04/15] ps3vram: Replace mutex by spinlock + list

On Fri, 8 May 2009, Andrew Morton wrote:
> On Fri,  8 May 2009 16:01:13 +0200
> Geert Uytterhoeven <Geert.Uytterhoeven@...ycom.com> wrote:
> 
> > +static int ps3vram_make_request(struct request_queue *q, struct bio *bio)
> > +{
> > +	struct ps3_system_bus_device *dev = q->queuedata;
> > +	struct ps3vram_priv *priv = dev->core.driver_data;
> > +
> > +	dev_dbg(&dev->core, "%s\n", __func__);
> > +
> > +	spin_lock_irq(&priv->lock);
> > +	if (priv->tail) {
> > +		priv->tail->bi_next = bio;
> > +		priv->tail = bio;
> > +		spin_unlock_irq(&priv->lock);
> > +		return 0;
                ^^^^^^^^
> > +	}
> > +
> > +	priv->tail = bio;
> > +	spin_unlock_irq(&priv->lock);
> > +
> > +	do {
> > +		bio = ps3vram_do_bio(dev, bio);
> > +	} while (bio);
> 
> Is there something which prevents two threads of control from walking
> the same list at the same time?

Sure: only the thread who adds the first request to the empty list will walk
the list later.

With kind regards,

Geert Uytterhoeven
Software Architect
Techsoft Centre

Technology and Software Centre Europe
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