[S390] subchannel register/unregister mutex.

Add a reg_mutex to prevent unregistering a subchannel before it has been
registered. Since 2.6.17, we've seen oopses in kslowcrw when a device is
found to be not operational during sense id when doing initial device
recognition; it is not clear yet why that particular problem was not (yet)
observed with earlier kernels...

Signed-off-by: Cornelia Huck <cornelia.huck@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/cio.h b/drivers/s390/cio/cio.h
index 0ca987344e07..4541c1af4b66 100644
--- a/drivers/s390/cio/cio.h
+++ b/drivers/s390/cio/cio.h
@@ -2,6 +2,7 @@
 #define S390_CIO_H
 
 #include "schid.h"
+#include <linux/mutex.h>
 
 /*
  * where we put the ssd info
@@ -87,7 +88,7 @@ struct orb {
 struct subchannel {
         struct subchannel_id schid;
         spinlock_t lock;        /* subchannel lock */
-
+        struct mutex reg_mutex;
         enum {
                 SUBCHANNEL_TYPE_IO = 0,
                 SUBCHANNEL_TYPE_CHSC = 1,