[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>

5 files changed, 29 insertions, 7 deletions

diff --git a/drivers/s390/cio/cio.c b/drivers/s390/cio/cio.c
index 6fec90eab00e..f27b2b866f5a 100644
--- a/drivers/s390/cio/cio.c
+++ b/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,
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,
diff --git a/drivers/s390/cio/css.c b/drivers/s390/cio/css.c
index 1d3be80797f8..a09deea5d687 100644
--- a/drivers/s390/cio/css.c
+++ b/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);
diff --git a/drivers/s390/cio/css.h b/drivers/s390/cio/css.h
index e210f89a2449..15f7f7cb0ec2 100644
--- a/drivers/s390/cio/css.h
+++ b/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 *);
diff --git a/drivers/s390/cio/device.c b/drivers/s390/cio/device.c
index 67f0de6aed33..9db09870b2ae 100644
--- a/drivers/s390/cio/device.c
+++ b/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);