[14/89] block: blkdev_get() should access ->bd_disk only after

[Greg KH]

2.6.39-stable review patch.  If anyone has any objections, please let us know.

------------------
 success

From: Tejun Heo <tj@xxxxxxxxxx>

commit 4c49ff3fe128ca68dabd07537415c419ad7f82f9 upstream.

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@xxxxxxxxxx>
Reported-by: David Miller <davem@xxxxxxxxxxxxx>
Tested-by: David Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Jens Axboe <jaxboe@xxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxx>

---
 fs/block_dev.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -1272,8 +1272,8 @@ int blkdev_get(struct block_device *bdev
 		 * 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);
 		}


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