Acked: [PATCH] block: blkdev_get() should access ->bd_disk only after success

[Seth Forshee]

On Tue, Oct 11, 2011 at 12:39:37PM -0300, Herton R. Krzesinski wrote:
> From: Tejun Heo <tj at kernel.org>
> 
> d4dc210f69 (block: don't block events on excl write for non-optical
> devices) added dereferencing of bdev->bd_disk to test
> GENHD_FL_BLOCK_EVENTS_ON_EXCL_WRITE; however, bdev->bd_disk can be
> %NULL if open failed which can lead to an oops.
> 
> Test the flag after testing open was successful, not before.
> 
> Signed-off-by: Tejun Heo <tj at kernel.org>
> Reported-by: David Miller <davem at davemloft.net>
> Tested-by: David Miller <davem at davemloft.net>
> Cc: stable at kernel.org
> Signed-off-by: Jens Axboe <jaxboe at fusionio.com>
> (cherry picked from commit 4c49ff3fe128ca68dabd07537415c419ad7f82f9)
> BugLink: http://bugs.launchpad.net/bugs/857170
> Signed-off-by: Herton Ronaldo Krzesinski <herton.krzesinski at canonical.com>
> ---
>  fs/block_dev.c |    4 ++--
>  1 files changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/block_dev.c b/fs/block_dev.c
> index 59277ba..0ce65c9 100644
> --- a/fs/block_dev.c
> +++ b/fs/block_dev.c
> @@ -1267,8 +1267,8 @@ int blkdev_get(struct block_device *bdev, fmode_t mode, void *holder)
>  		 * individual writeable reference is too fragile given the
>  		 * way @mode is used in blkdev_get/put().
>  		 */
> -		if ((disk->flags & GENHD_FL_BLOCK_EVENTS_ON_EXCL_WRITE) &&
> -		    !res && (mode & FMODE_WRITE) && !bdev->bd_write_holder) {
> +		if (!res && (mode & FMODE_WRITE) && !bdev->bd_write_holder &&
> +		    (disk->flags & GENHD_FL_BLOCK_EVENTS_ON_EXCL_WRITE)) {
>  			bdev->bd_write_holder = true;
>  			disk_block_events(disk);
>  		}

Acked-by: Seth Forshee <seth.forshee at canonical.com>