[S390] cio: fix double unregistering of subchannels

In some cases where the channel subsystem decides to drop a subchannel
device device_unregister may be called twice, which results in an oops.
The patch prevents this by only unregistering registered devices.

Signed-off-by: Sebastian Ott <sebott@linux.vnet.ibm.com>
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

1 files changed, 2 insertions, 1 deletions

diff --git a/drivers/s390/cio/css.c b/drivers/s390/cio/css.c
index 4e2f2bbf4ba5..46c021d880dc 100644
--- a/drivers/s390/cio/css.c
+++ b/drivers/s390/cio/css.c
@@ -164,7 +164,8 @@ static int css_sch_device_register(struct subchannel *sch)
 void css_sch_device_unregister(struct subchannel *sch)
 {
         mutex_lock(&sch->reg_mutex);
-        device_unregister(&sch->dev);
+        if (device_is_registered(&sch->dev))
+                device_unregister(&sch->dev);
         mutex_unlock(&sch->reg_mutex);
 }
 EXPORT_SYMBOL_GPL(css_sch_device_unregister);