Commit 7fd152f4 authored by Daniel Stodden's avatar Daniel Stodden Committed by Jens Axboe
Browse files

blkfront: Fix blkfront backend switch race (bdev release) 



We cannot read backend state within bdev operations, because it risks
grabbing the state change before xenbus gets to do it.

Fixed by tracking deferral with a frontend switch to Closing. State
exposure isn't strictly necessary, but the backends won't mind.

For a 'clean' deferral this seems actually a more decent protocol than
raising errors.

Signed-off-by: default avatarDaniel Stodden <daniel.stodden@citrix.com>
Signed-off-by: default avatarJeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Signed-off-by: default avatarJens Axboe <jaxboe@fusionio.com>
parent 13961743

drivers/block/xen-blkfront.c

+33 −16
Original line number Original line Diff line number Diff line
@@ -1142,31 +1142,48 @@ static int blkif_open(struct block_device *bdev, fmode_t mode) 
	if (!err)

	if (!err)

		++info->users;

		++info->users;





	unlock_kernel();

out:

out:

	unlock_kernel();

	return err;

	return err;

}

}





static int blkif_release(struct gendisk *disk, fmode_t mode)

static int blkif_release(struct gendisk *disk, fmode_t mode)

{

{

	struct blkfront_info *info = disk->private_data;

	struct blkfront_info *info = disk->private_data;

	struct block_device *bdev;

	struct xenbus_device *xbdev;



	lock_kernel();

	lock_kernel();

	info->users--;

	if (--info->users)

	if (info->users == 0) {

		goto out;

		/* Check whether we have been instructed to close.  We will



		   have ignored this request initially, as the device was

	bdev = bdget_disk(disk, 0);

		   still mounted. */

	bdput(bdev);

		struct xenbus_device *dev = info->xbdev;





	/*

		if (!dev) {

	 * Check if we have been instructed to close. We will have

			xlvbd_release_gendisk(info);

	 * deferred this request, because the bdev was still open.

			kfree(info);

	 */

		} else if (xenbus_read_driver_state(dev->otherend)



			   == XenbusStateClosing && info->is_ready) {

	mutex_lock(&info->mutex);

	xbdev = info->xbdev;



	if (xbdev && xbdev->state == XenbusStateClosing) {

		/* pending switch to state closed */

		xlvbd_release_gendisk(info);

		xlvbd_release_gendisk(info);

			xenbus_frontend_closed(dev);

		xenbus_frontend_closed(info->xbdev);

 	}

 	}



	mutex_unlock(&info->mutex);



	if (!xbdev) {

		/* sudden device removal */

		xlvbd_release_gendisk(info);

		disk->private_data = NULL;

		kfree(info);

	}

	}



out:

	unlock_kernel();

	unlock_kernel();

	return 0;

	return 0;

}

}