linux-kernel - Re: [PATCH 01/17] MTD: create lockless versions of {get,put}_mtd_device This will be used to resolve deadlock in block translation layer.

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Message-ID: <1265735693.11509.253.camel@laptop>
Date:	Tue, 09 Feb 2010 18:14:53 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Maxim Levitsky <maximlevitsky@...il.com>
Cc:	David Woodhouse <dwmw2@...radead.org>,
	Artem Bityutskiy <dedekind1@...il.com>,
	linux-mtd <linux-mtd@...ts.infradead.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Alex Dubov <oakad@...oo.com>, joern <joern@...fs.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	"stanley.miao" <stanley.miao@...driver.com>,
	Vitaly Wool <vitalywool@...il.com>
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.

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@...il.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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