linux-kernel - Re: [PATCH] mtd: fix: avoid race condition when accessing mtd->usecount

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Date:	Tue, 12 May 2015 18:37:04 +0200
From:	Alexander Sverdlin <alexander.sverdlin@...ia.com>
To:	ext Brian Norris <computersforpeace@...il.com>,
	Giuseppe Cantavenera <giuseppe.cantavenera.ext@...ia.com>
CC:	linux-mtd@...ts.infradead.org, lorenzo.restelli.ext@...ia.com,
	dwmw2@...radead.org, stable@...r.kernel.org,
	zhangxingcai <zhangxingcai@...wei.com>, fengfuqiu@...wei.com,
	tanhaijun@...wei.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mtd: fix: avoid race condition when accessing mtd->usecount

On 08/05/15 02:26, ext Brian Norris wrote:
> As an alternative to your patch, how about the following?
> 
> BTW, this does still leave a usecount race in
> drivers/mtd/maps/vmu-flash.c. But that driver should really be using
> mtd->_get_device(), if it actually wants its own refcount.
> 
> Signed-off-by: Brian Norris <computersforpeace@...il.com>

Acked-by: Alexander Sverdlin <alexander.sverdlin@...ia.com>

> ---
> 
> diff --git a/drivers/mtd/mtd_blkdevs.c b/drivers/mtd/mtd_blkdevs.c
> index 2b0c52870999..df7c6c70757a 100644
> --- a/drivers/mtd/mtd_blkdevs.c
> +++ b/drivers/mtd/mtd_blkdevs.c
> @@ -197,6 +197,7 @@ static int blktrans_open(struct block_device *bdev, fmode_t mode)
>  		return -ERESTARTSYS; /* FIXME: busy loop! -arnd*/
>  
>  	mutex_lock(&dev->lock);
> +	mutex_lock(&mtd_table_mutex);
>  
>  	if (dev->open)
>  		goto unlock;
> @@ -220,6 +221,7 @@ static int blktrans_open(struct block_device *bdev, fmode_t mode)
>  
>  unlock:
>  	dev->open++;
> +	mutex_unlock(&mtd_table_mutex);
>  	mutex_unlock(&dev->lock);
>  	blktrans_dev_put(dev);
>  	return ret;
> @@ -230,6 +232,7 @@ error_release:
>  error_put:
>  	module_put(dev->tr->owner);
>  	kref_put(&dev->ref, blktrans_dev_release);
> +	mutex_unlock(&mtd_table_mutex);
>  	mutex_unlock(&dev->lock);
>  	blktrans_dev_put(dev);
>  	return ret;
> @@ -243,6 +246,7 @@ static void blktrans_release(struct gendisk *disk, fmode_t mode)
>  		return;
>  
>  	mutex_lock(&dev->lock);
> +	mutex_lock(&mtd_table_mutex);
>  
>  	if (--dev->open)
>  		goto unlock;
> @@ -256,6 +260,7 @@ static void blktrans_release(struct gendisk *disk, fmode_t mode)
>  		__put_mtd_device(dev->mtd);
>  	}
>  unlock:
> +	mutex_unlock(&mtd_table_mutex);
>  	mutex_unlock(&dev->lock);
>  	blktrans_dev_put(dev);
>  }
--
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