[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>

drivers/s390/cio/cio.c

@@ -519,6 +519,7 @@ cio_validate_subchannel (struct subchannel *sch, struct subchannel_id schid)
 	memset(sch, 0, sizeof(struct subchannel));
 
 	spin_lock_init(&sch->lock);
+	mutex_init(&sch->reg_mutex);
 
 	/* Set a name for the subchannel */
 	snprintf (sch->dev.bus_id, BUS_ID_SIZE, "0.%x.%04x", schid.ssid,

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,

drivers/s390/cio/css.c

@@ -108,6 +108,24 @@ css_subchannel_release(struct device *dev)
 
 extern int css_get_ssd_info(struct subchannel *sch);
 
+
+int css_sch_device_register(struct subchannel *sch)
+{
+	int ret;
+
+	mutex_lock(&sch->reg_mutex);
+	ret = device_register(&sch->dev);
+	mutex_unlock(&sch->reg_mutex);
+	return ret;
+}
+
+void css_sch_device_unregister(struct subchannel *sch)
+{
+	mutex_lock(&sch->reg_mutex);
+	device_unregister(&sch->dev);
+	mutex_unlock(&sch->reg_mutex);
+}
+
 static int
 css_register_subchannel(struct subchannel *sch)
 {
@@ -119,7 +137,7 @@ css_register_subchannel(struct subchannel *sch)
 	sch->dev.release = &css_subchannel_release;
 	
 	/* make it known to the system */
-	ret = device_register(&sch->dev);
+	ret = css_sch_device_register(sch);
 	if (ret)
 		printk (KERN_WARNING "%s: could not register %s\n",
 			__func__, sch->dev.bus_id);
@@ -250,7 +268,7 @@ css_evaluate_subchannel(struct subchannel_id schid, int slow)
 		 * The device will be killed automatically.
 		 */
 		cio_disable_subchannel(sch);
-		device_unregister(&sch->dev);
+		css_sch_device_unregister(sch);
 		/* Reset intparm to zeroes. */
 		sch->schib.pmcw.intparm = 0;
 		cio_modify(sch);
@@ -264,7 +282,7 @@ css_evaluate_subchannel(struct subchannel_id schid, int slow)
 		 * away in any case.
 		 */
 		if (!disc) {
-			device_unregister(&sch->dev);
+			css_sch_device_unregister(sch);
 			/* Reset intparm to zeroes. */
 			sch->schib.pmcw.intparm = 0;
 			cio_modify(sch);

drivers/s390/cio/css.h

@@ -136,6 +136,8 @@ extern struct bus_type css_bus_type;
 extern struct css_driver io_subchannel_driver;
 
 extern int css_probe_device(struct subchannel_id);
+extern int css_sch_device_register(struct subchannel *);
+extern void css_sch_device_unregister(struct subchannel *);
 extern struct subchannel * get_subchannel_by_schid(struct subchannel_id);
 extern int css_init_done;
 extern int for_each_subchannel(int(*fn)(struct subchannel_id, void *), void *);

drivers/s390/cio/device.c

@@ -280,7 +280,7 @@ ccw_device_remove_disconnected(struct ccw_device *cdev)
 	 * 'throw away device'.
 	 */
 	sch = to_subchannel(cdev->dev.parent);
-	device_unregister(&sch->dev);
+	css_sch_device_unregister(sch);
 	/* Reset intparm to zeroes. */
 	sch->schib.pmcw.intparm = 0;
 	cio_modify(sch);
@@ -625,7 +625,7 @@ ccw_device_do_unreg_rereg(void *data)
 					other_sch->schib.pmcw.intparm = 0;
 					cio_modify(other_sch);
 				}
-				device_unregister(&other_sch->dev);
+				css_sch_device_unregister(other_sch);
 			}
 		}
 		/* Update ssd info here. */
@@ -709,7 +709,7 @@ ccw_device_call_sch_unregister(void *data)
 	struct subchannel *sch;
 
 	sch = to_subchannel(cdev->dev.parent);
-	device_unregister(&sch->dev);
+	css_sch_device_unregister(sch);
 	/* Reset intparm to zeroes. */
 	sch->schib.pmcw.intparm = 0;
 	cio_modify(sch);