Hello,

On Mon, Oct 21, 2013 at 02:52:41PM +0530, Rashika Kheria wrote:
> This patch fixes the following Smatch warning in zram_drv.c-
> drivers/staging/zram/zram_drv.c:663
> reset_store() warn: variable dereferenced before check 'bdev' (see line 652)
> drivers/staging/zram/zram_drv.c:899
> destroy_device() warn: variable dereferenced before check 'zram->disk' (see 
> line 896)
> 
> Signed-off-by: Rashika Kheria <rashika.khe...@gmail.com>
> ---
> 
> This revision fixes the following issues of the previous revision-
> Not included null check
> 
>  drivers/staging/zram/zram_drv.c |   11 ++++++-----
>  1 file changed, 6 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/staging/zram/zram_drv.c b/drivers/staging/zram/zram_drv.c
> index 2c4ed52..5594d5b 100644
> --- a/drivers/staging/zram/zram_drv.c
> +++ b/drivers/staging/zram/zram_drv.c
> @@ -648,6 +648,9 @@ static ssize_t reset_store(struct device *dev,
>       zram = dev_to_zram(dev);
>       bdev = bdget_disk(zram->disk, 0);
>  
> +     if (!bdev)
> +             return -EBUSY;
> +

I'm not an expert on sysfs and block so it's hard to understand
when we could see NULL bdev in reset handler.
I hope others could answer it.

Another thing, when I review the code, I found it has a bug.
reset_store doesn't put refcount by getting one by bdget_disk.
It should be fixed, I think.

>       /* Do not reset an active device! */
>       if (bdev->bd_holders)
>               return -EBUSY;
> @@ -660,8 +663,7 @@ static ssize_t reset_store(struct device *dev,
>               return -EINVAL;
>  
>       /* Make sure all pending I/O is finished */
> -     if (bdev)
> -             fsync_bdev(bdev);
> +     fsync_bdev(bdev);
>  

>       zram_reset_device(zram, true);
>       return len;
> @@ -893,10 +895,9 @@ out:
>  
>  static void destroy_device(struct zram *zram)
>  {
> -     sysfs_remove_group(&disk_to_dev(zram->disk)->kobj,
> -                     &zram_disk_attr_group);
> -
>       if (zram->disk) {
> +             sysfs_remove_group(&disk_to_dev(zram->disk)->kobj,
> +                             &zram_disk_attr_group);

Is it really necessary to check zram->disk and zram->queue in this function?
As I see code roughly, it seems to be not necessary but need double check.
If so, please remove the check code.



>               del_gendisk(zram->disk);
>               put_disk(zram->disk);
>       }
> -- 
> 1.7.9.5
> 

-- 
Kind regards,
Minchan Kim
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