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Commit 0f57c97f authored by Jan Höppner's avatar Jan Höppner Committed by Martin Schwidefsky
Browse files

s390/dasd: Eliminate race condition in dasd_generic_set_offline() 



Before we set a device offline, the open_count for the block device is
checked and certain flags are checked and set as well.
However, this is all done without holding any lock. Potentially, if the
open_count was checked but the DASD_FLAG_OFFLINE wasn't set yet, a
different process might want to increase the open_count depending on
whether DASD_FLAG_OFFLINE is set or not in the meanwhile.

This is quite racy and can lead to the loss of the device for that
process and subsequently lead to a panic.

Fix this by checking the open_count and setting the offline flags while
holding the ccwdev lock.

Reviewed-by: default avatarStefan Haberland <sth@linux.vnet.ibm.com>
Signed-off-by: default avatarJan Höppner <hoeppner@linux.vnet.ibm.com>
Signed-off-by: default avatarMartin Schwidefsky <schwidefsky@de.ibm.com>
parent 1081f3a7

drivers/s390/block/dasd.c

+24 −15
Original line number Diff line number Diff line
@@ -3517,11 +3517,15 @@ int dasd_generic_set_offline(struct ccw_device *cdev) 
	struct dasd_device *device;

	struct dasd_block *block;

	int max_count, open_count, rc;

	unsigned long flags;



	rc = 0;

	device = dasd_device_from_cdev(cdev);

	if (IS_ERR(device))

	spin_lock_irqsave(get_ccwdev_lock(cdev), flags);

	device = dasd_device_from_cdev_locked(cdev);

	if (IS_ERR(device)) {

		spin_unlock_irqrestore(get_ccwdev_lock(cdev), flags);

		return PTR_ERR(device);

	}



	/*

	 * We must make sure that this device is currently not in use.
@@ -3540,8 +3544,7 @@ int dasd_generic_set_offline(struct ccw_device *cdev) 
				pr_warn("%s: The DASD cannot be set offline while it is in use\n",

					dev_name(&cdev->dev));

			clear_bit(DASD_FLAG_OFFLINE, &device->flags);

			dasd_put_device(device);

			return -EBUSY;

			goto out_busy;

		}

	}
@@ -3551,20 +3554,20 @@ int dasd_generic_set_offline(struct ccw_device *cdev) 
		 * could only be called by normal offline so safe_offline flag

		 * needs to be removed to run normal offline and kill all I/O

		 */

		if (test_and_set_bit(DASD_FLAG_OFFLINE, &device->flags)) {

		if (test_and_set_bit(DASD_FLAG_OFFLINE, &device->flags))

			/* Already doing normal offline processing */

			dasd_put_device(device);

			return -EBUSY;

		} else

			goto out_busy;

		else

			clear_bit(DASD_FLAG_SAFE_OFFLINE, &device->flags);



	} else

		if (test_bit(DASD_FLAG_OFFLINE, &device->flags)) {

	} else {

		if (test_bit(DASD_FLAG_OFFLINE, &device->flags))

			/* Already doing offline processing */

			dasd_put_device(device);

			return -EBUSY;

			goto out_busy;

	}



	set_bit(DASD_FLAG_OFFLINE, &device->flags);

	spin_unlock_irqrestore(get_ccwdev_lock(cdev), flags);



	/*

	 * if safe_offline called set safe_offline_running flag and

	 * clear safe_offline so that a call to normal offline
@@ -3591,7 +3594,6 @@ int dasd_generic_set_offline(struct ccw_device *cdev) 
			goto interrupted;

	}



	set_bit(DASD_FLAG_OFFLINE, &device->flags);

	dasd_set_target_state(device, DASD_STATE_NEW);

	/* dasd_delete_device destroys the device reference. */

	block = device->block;
@@ -3610,7 +3612,14 @@ int dasd_generic_set_offline(struct ccw_device *cdev) 
	clear_bit(DASD_FLAG_SAFE_OFFLINE_RUNNING, &device->flags);

	clear_bit(DASD_FLAG_OFFLINE, &device->flags);

	dasd_put_device(device);



	return rc;



out_busy:

	dasd_put_device(device);

	spin_unlock_irqrestore(get_ccwdev_lock(cdev), flags);



	return -EBUSY;

}

EXPORT_SYMBOL_GPL(dasd_generic_set_offline);