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

[Tim Gardner]

On 10/11/2011 04:39 PM, 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);
>   		}


-- 
Tim Gardner tim.gardner at canonical.com