Subject: Re: [PATCH 01/17] MTD: create lockless versions of
 {get,put}_mtd_device This will be used to resolve deadlock in block
 translation layer.
From: Peter Zijlstra <peterz@infradead.org>
To: Maxim Levitsky <maximlevitsky@gmail.com>
Cc: David Woodhouse <dwmw2@infradead.org>,
       Artem Bityutskiy <dedekind1@gmail.com>,
       linux-mtd <linux-mtd@lists.infradead.org>,
       linux-kernel <linux-kernel@vger.kernel.org>,
       Alex Dubov <oakad@yahoo.com>, joern <joern@logfs.org>,
       Thomas Gleixner <tglx@linutronix.de>,
       "stanley.miao" <stanley.miao@windriver.com>,
       Vitaly Wool <vitalywool@gmail.com>
In-Reply-To: <1265734665-22656-2-git-send-email-maximlevitsky@gmail.com>
References: <1265734665-22656-1-git-send-email-maximlevitsky@gmail.com>
	 <1265734665-22656-2-git-send-email-maximlevitsky@gmail.com>
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Date: Tue, 09 Feb 2010 18:14:53 +0100
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On Tue, 2010-02-09 at 18:57 +0200, Maxim Levitsky wrote:
> These functions can be used as long as we don't need access to global mtd table, but have
> a pointer to the mtd device.
> 
> Signed-off-by: Maxim Levitsky <maximlevitsky@gmail.com>
> ---
>  drivers/mtd/mtdcore.c   |   60 ++++++++++++++++++++++++++++++----------------
>  include/linux/mtd/mtd.h |    3 +-
>  2 files changed, 41 insertions(+), 22 deletions(-)

> +int __get_mtd_device(struct mtd_info *mtd)
> +{
> +	int err;
> +
> +	if (!try_module_get(mtd->owner))
> +		return -ENODEV;
> +
> +	if (mtd->get_device) {
> +
> +		err = mtd->get_device(mtd);
> +
> +		if (err) {
> +			module_put(mtd->owner);
> +			return err;
> +		}
> +	}
> +	mtd->usecount++;
> +	return 0;
>  }

> +void __put_mtd_device(struct mtd_info *mtd)
> +{
> +	--mtd->usecount;
> +	BUG_ON(mtd->usecount < 0);
> +
>  	if (mtd->put_device)
>  		mtd->put_device(mtd);
>  
>  	module_put(mtd->owner);
>  }

That's racy, use kref.

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