linux-kernel - Re: [PATCH v8 2/3] Staging: zram: Fix decrement of variable by calling bdput()

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Date:	Thu, 31 Oct 2013 17:42:06 +0800
From:	Weijie Yang <weijie.yang.kh@...il.com>
To:	Rashika Kheria <rashika.kheria@...il.com>
Cc:	opw-kernel@...glegroups.com, Minchan Kim <minchan@...nel.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Jiang Liu <jiang.liu@...wei.com>,
	Nitin Gupta <ngupta@...are.org>,
	Jerome Marchand <jmarchand@...hat.com>,
	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH v8 2/3] Staging: zram: Fix decrement of variable by
 calling bdput()

Hello, Rashika

On Wed, Oct 30, 2013 at 9:10 PM, Rashika Kheria
<rashika.kheria@...il.com> wrote:
> As suggested by Jerome Marchand "The code in reset_store get the block device
> (bdget_disk()) but it does not put it (bdput()) when it's done using it.
> The usage count is therefore incremented but never decremented."
>
> This patch also puts bdput() for all error cases.
>
> Cc: stable@...r.kernel.org
> Signed-off-by: Rashika Kheria <rashika.kheria@...il.com>
> ---
>
> This revision fixes the following issues of the previous revision-
> Proper error handling
>
>  drivers/staging/zram/zram_drv.c |   25 ++++++++++++++++++-------
>  1 file changed, 18 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/staging/zram/zram_drv.c b/drivers/staging/zram/zram_drv.c
> index 012ba15..0bc2835 100644
> --- a/drivers/staging/zram/zram_drv.c
> +++ b/drivers/staging/zram/zram_drv.c
> @@ -648,25 +648,36 @@ static ssize_t reset_store(struct device *dev,
>         zram = dev_to_zram(dev);
>         bdev = bdget_disk(zram->disk, 0);
>
> -       if (!bdev)
> -               return -ENOMEM;
> +       if (!bdev) {
> +               ret = -ENOMEM;
> +               goto out;
> +       }

If bdev is NULL, just return -ENOMEM; DO NOT goto out;
or you will get a NULL point reference in bdput(bdev);

>         /* Do not reset an active device! */
> -       if (bdev->bd_holders)
> -               return -EBUSY;
> +       if (bdev->bd_holders) {
> +               ret = -EBUSY;
> +               goto out;
> +       }
>
>         ret = kstrtou16(buf, 10, &do_reset);
>         if (ret)
> -               return ret;
> +               goto out;
>
> -       if (!do_reset)
> -               return -EINVAL;
> +       if (!do_reset) {
> +               ret = -EINVAL;
> +               goto out;
> +       }
>
>         /* Make sure all pending I/O is finished */
>         fsync_bdev(bdev);
> +       bdput(bdev);
>
>         zram_reset_device(zram, true);
>         return len;
> +
> +out:
> +       bdput(bdev);
> +       return ret;
>  }
>
>  static void __zram_make_request(struct zram *zram, struct bio *bio, int rw)
> --
> 1.7.9.5
>
> --
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