[S390] cio: prevent purging of CCW devices in the online state

The cio_ignore purge function is intended to only remove CCW devices
which are in the offline state. There is a time frame after the purge
function finished where a CCW device is scheduled for removal but
still accessible. When the device is set online during this time
frame, it may first appear online before it is then removed.

Fix this by preventing that CCW devices can be set online while there
is work (such as removal triggered by the purge function) for it
pending. Also ensure that the purge function does not schedule devices
for removal which are in the process of being set online.
Signed-off-by: Peter Oberparleiter <peter.oberparleiter@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

drivers/s390/cio/device.c

@@ -541,15 +541,24 @@ static ssize_t online_store (struct device *dev, struct device_attribute *attr,
 	int force, ret;
 	unsigned long i;
 
-	if (!dev_fsm_final_state(cdev) &&
-	    cdev->private->state != DEV_STATE_DISCONNECTED)
-		return -EAGAIN;
+	/* Prevent conflict between multiple on-/offline processing requests. */
 	if (atomic_cmpxchg(&cdev->private->onoff, 0, 1) != 0)
 		return -EAGAIN;
+	/* Prevent conflict between internal I/Os and on-/offline processing. */
+	if (!dev_fsm_final_state(cdev) &&
+	    cdev->private->state != DEV_STATE_DISCONNECTED) {
+		ret = -EAGAIN;
+		goto out_onoff;
+	}
+	/* Prevent conflict between pending work and on-/offline processing.*/
+	if (work_pending(&cdev->private->todo_work)) {
+		ret = -EAGAIN;
+		goto out_onoff;
+	}
 
 	if (cdev->drv && !try_module_get(cdev->drv->driver.owner)) {
-		atomic_set(&cdev->private->onoff, 0);
-		return -EINVAL;
+		ret = -EINVAL;
+		goto out_onoff;
 	}
 	if (!strncmp(buf, "force\n", count)) {
 		force = 1;
@@ -574,6 +583,7 @@ static ssize_t online_store (struct device *dev, struct device_attribute *attr,
 out:
 	if (cdev->drv)
 		module_put(cdev->drv->driver.owner);
+out_onoff:
 	atomic_set(&cdev->private->onoff, 0);
 	return (ret < 0) ? ret : count;
 }
@@ -1311,10 +1321,12 @@ static int purge_fn(struct device *dev, void *data)
 
 	spin_lock_irq(cdev->ccwlock);
 	if (is_blacklisted(id->ssid, id->devno) &&
-	    (cdev->private->state == DEV_STATE_OFFLINE)) {
+	    (cdev->private->state == DEV_STATE_OFFLINE) &&
+	    (atomic_cmpxchg(&cdev->private->onoff, 0, 1) == 0)) {
 		CIO_MSG_EVENT(3, "ccw: purging 0.%x.%04x\n", id->ssid,
 			      id->devno);
 		ccw_device_sched_todo(cdev, CDEV_TODO_UNREG);
+		atomic_set(&cdev->private->onoff, 0);
 	}
 	spin_unlock_irq(cdev->ccwlock);
 	/* Abort loop in case of pending signal. */