linux-kernel - Re: [PATCHv3 9/9] zram: add dynamic device add/remove functionality

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Date:	Mon, 4 May 2015 20:34:40 +0900
From:	Sergey Senozhatsky <sergey.senozhatsky@...il.com>
To:	Minchan Kim <minchan@...nel.org>
Cc:	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Nitin Gupta <ngupta@...are.org>, linux-kernel@...r.kernel.org,
	Sergey Senozhatsky <sergey.senozhatsky@...il.com>
Subject: Re: [PATCHv3 9/9] zram: add dynamic device add/remove functionality

> diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
> index 3df4394..7fb72dc 100644
> --- a/drivers/block/zram/zram_drv.c
> +++ b/drivers/block/zram/zram_drv.c
> @@ -1074,13 +1074,6 @@ static ssize_t reset_store(struct device *dev,
>  	if (!bdev)
>  		return -ENOMEM;
>  
> -	mutex_lock(&bdev->bd_mutex);
> -	/* Do not reset an active device! */
> -	if (bdev->bd_openers) {
> -		ret = -EBUSY;
> -		goto out;
> -	}
> -
>  	ret = kstrtou16(buf, 10, &do_reset);
>  	if (ret)
>  		goto out;
> @@ -1090,23 +1083,52 @@ static ssize_t reset_store(struct device *dev,
>  		goto out;
>  	}
>  
> +	mutex_lock(&bdev->bd_mutex);
> +	/* Do not reset an active device or claimed device */
> +	if (bdev->bd_openers || zram->claim) {
> +		ret = -EBUSY;
> +		mutex_unlock(&bdev->bd_mutex);
> +		goto out;
> +	}
> +
> +	/* From now on, anyone can't open /dev/zram[0-9] */
> +	zram->claim = true;
> +	mutex_unlock(&bdev->bd_mutex);
> +
>  	/* Make sure all pending I/O is finished */
>  	fsync_bdev(bdev);
>  	zram_reset_device(zram);
>  
> -	mutex_unlock(&bdev->bd_mutex);
>  	revalidate_disk(zram->disk);
>  	bdput(bdev);
>  
> -	return len;
> +	mutex_lock(&bdev->bd_mutex);
> +	zram->claim = false;
> +	mutex_unlock(&bdev->bd_mutex);
>  
> +	return len;
>  out:
> -	mutex_unlock(&bdev->bd_mutex);
>  	bdput(bdev);
>  	return ret;

just backported reset_store() simplification from my another patch.

make validation outisde of ->bd_mutex and before we inc ndev ref
counter in bdget_disk(). this also makes it possible to get rid of
goto label.

the rest looks ok to me. will fold into your patch and submit.

---

diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index 7fb72dc..f50bd66 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -1068,27 +1068,24 @@ static ssize_t reset_store(struct device *dev,
        struct zram *zram;
        struct block_device *bdev;
 
+       ret = kstrtou16(buf, 10, &do_reset);
+       if (ret)
+               return ret;
+
+       if (!do_reset)
+               return -EINVAL;
+
        zram = dev_to_zram(dev);
        bdev = bdget_disk(zram->disk, 0);
-
        if (!bdev)
                return -ENOMEM;
 
-       ret = kstrtou16(buf, 10, &do_reset);
-       if (ret)
-               goto out;
-
-       if (!do_reset) {
-               ret = -EINVAL;
-               goto out;
-       }
-
        mutex_lock(&bdev->bd_mutex);
        /* Do not reset an active device or claimed device */
        if (bdev->bd_openers || zram->claim) {
-               ret = -EBUSY;
                mutex_unlock(&bdev->bd_mutex);
-               goto out;
+               bdput(bdev);
+               return -EBUSY;
        }
 
        /* From now on, anyone can't open /dev/zram[0-9] */
@@ -1107,9 +1104,6 @@ static ssize_t reset_store(struct device *dev,
        mutex_unlock(&bdev->bd_mutex);
 
        return len;
-out:
-       bdput(bdev);
-       return ret;
 }
 
 static int zram_open(struct block_device *bdev, fmode_t mode)

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