[S390] cio: Only register ccw_device for registered subchannel.

There is a race between io_subchannel_register() and
io_subchannel_sch_event() which may cause a subchannel to be
unregistered because it is no longer operational before
io_subchannel_register() had run. We need to check whether the
subchannel is still registered before the ccw device can be
registered and just bail out if it is not.

Signed-off-by: Cornelia Huck <cornelia.huck@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

1 files changed, 12 insertions, 6 deletions

diff --git a/drivers/s390/cio/device.c b/drivers/s390/cio/device.c
index cba33aa1df7..91acea10840 100644
--- a/drivers/s390/cio/device.c
+++ b/drivers/s390/cio/device.c
@@ -950,6 +950,14 @@ io_subchannel_register(struct work_struct *work)
         priv = container_of(work, struct ccw_device_private, kick_work);
         cdev = priv->cdev;
         sch = to_subchannel(cdev->dev.parent);
+        /*
+         * Check if subchannel is still registered. It may have become
+         * unregistered if a machine check hit us after finishing
+         * device recognition but before the register work could be
+         * queued.
+         */
+        if (!device_is_registered(&sch->dev))
+                goto out_err;
         css_update_ssd_info(sch);
         /*
          * io_subchannel_register() will also be called after device
@@ -984,18 +992,16 @@ io_subchannel_register(struct work_struct *work)
                 spin_lock_irqsave(sch->lock, flags);
                 sch_set_cdev(sch, NULL);
                 spin_unlock_irqrestore(sch->lock, flags);
-                /* Release reference for workqueue processing. */
-                put_device(&cdev->dev);
                 /* Release initial device reference. */
                 put_device(&cdev->dev);
-                if (atomic_dec_and_test(&ccw_device_init_count))
-                        wake_up(&ccw_device_init_wq);
-                return;
+                goto out_err;
         }
-        put_device(&cdev->dev);
 out:
         cdev->private->flags.recog_done = 1;
         wake_up(&cdev->private->wait_q);
+out_err:
+        /* Release reference for workqueue processing. */
+        put_device(&cdev->dev);
         if (atomic_dec_and_test(&ccw_device_init_count))
                 wake_up(&ccw_device_init_wq);
 }